ecp 11-0003 testing and commissioning guidance...

Document Number: ECP 11-0003

Version: 4.0

Date: 10/02/2017

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ENGINEERING COMMISSIONING PROCEDURE

ECP 11-0003

TESTING AND COMMISSIONING GUIDANCE NOTES

Network(s): EPN, LPN, SPN

Summary: This document provides guidelines and preferred practices for the safe and effective testing, pre-commissioning and commissioning of electrical plant and associated protection and control equipment installed on UK Power Networks distribution networks.

Author: Stephen Tucker Date: 10/02/2017

Approved By: Paul Williams Approved Date: 16/02/2017

This document forms part of the Company’s Integrated Business System and its requirements are mandatory throughout UK Power Networks. Departure from these requirements may only be taken with the written approval of the Director of Asset Management. If you have any queries about this document please contact the author or owner of the current issue.

Applicable To

UK Power Networks External

☒ Asset Management ☒ G81 Website

☒ Capital Programme ☒ Contractors

☒ Connections ☒ ICPs/IDNOs

☒ Health & Safety ☐ Meter Operators

☒ Network Operations

☐ Procurement

☒ Technical Training

☐ UK Power Networks Services

Testing and Commissioning Guidance Notes Document Number: ECP 11-0003

Version: 4.0

Date: 10/02/2017

© UK Power Networks 2017 All rights reserved 2 of 48

Revision Record

Version 4.0 Review Date 10/02/2022

Date 10/02/2017 Author Stephen Tucker

Why has the document been updated: Alignment with other referenced documents.

What has changed:

Document references updated (Sections 4, 4.4, 8 and 20)

Renumbered from ECS 11-0003 to ECP 11-0003

Document reviewed and review date extended

Version 3.0 Review Date

Date 18/03/2014 Author Philip Bennett

Renumbered from ECP 11-0101 to ECS 11-0003. Reviewed and reformatted for G81 website

Version 2.0 Review Date Kevin Burt

Date 19/06/2012 Author

Modified to include requirements for checking site and plant cleanliness

Version 1.1 Review Date John Lowe

Date 11/03/2011 Author

Document rebranded

Version 1.0 Review Date

Date 17/11/2004 Author Stephen Tucker

Original


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Contents

1 Introduction ............................................................................................................. 6

2 Scope ....................................................................................................................... 6

3 Glossary and Abbreviations ................................................................................... 7

4 Co-ordination and Delegation of Commissioning Work ....................................... 8

4.1 Commissioning Personnel ......................................................................................... 8

4.2 Commencement of Testing ........................................................................................ 8

4.3 Quality Control and Attention to Detail ....................................................................... 8

4.4 Safe Working Practices ............................................................................................. 9

4.5 Documentary Records of Protection and Control Equipment ..................................... 9

4.6 Recording of Test Results ......................................................................................... 9

5 Inspection and Testing Order ............................................................................... 10

6 Guidance on Measuring Instrumentation Practice .............................................. 11

6.1 Choice and Use of Test Instruments ........................................................................ 11

6.2 General Measuring Instrument Practice ................................................................... 12

6.3 Measuring Large Quantities ..................................................................................... 12

6.4 Safety Precautions when using Instruments ............................................................ 12

7 Inspection of Plant ................................................................................................ 13

7.1 Switchgear and Conductors ..................................................................................... 13

7.1.1 Resistance Measurements ...................................................................................... 13

7.2 Distribution Transformers ........................................................................................ 14

7.3 Primary System Transformers ................................................................................. 14

8 High Voltage Pressure (Dielectric) Testing .......................................................... 16

9 Wiring Insulation Resistance Tests...................................................................... 17

9.1 Circuits to be Tested ................................................................................................ 17

9.2 Precautions ............................................................................................................. 18

9.3 Test Voltage and Results......................................................................................... 18

9.4 CT Secondary Circuits ............................................................................................. 18

10 Loop Resistance Tests ......................................................................................... 19

10.1 Current Transformer Secondary Circuits ................................................................. 19

10.2 Pilot Wires ............................................................................................................... 19

10.3 Other Circuits .......................................................................................................... 19

11 Current Transformer Magnetisation Curves ........................................................ 20

12 Secondary Injection and Protection Relay Tests ................................................ 22

12.1 Secondary Injection Applied to Current Operated Measuring Relays ....................... 22

12.2 IDMT Relay Operation and Timing Tests ................................................................. 23


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12.3 IDMT Timing Accuracy ............................................................................................ 24

12.3.1 Start Timing Function .............................................................................................. 24

12.3.2 Electromagnetic Relay ............................................................................................. 24

12.3.3 Electronic Relays ..................................................................................................... 24

12.4 Instantaneous Relays .............................................................................................. 25

12.5 Complex Protection Relays ..................................................................................... 25

12.6 Voltage Operated Relays in High Impedance Schemes .......................................... 25

12.7 All or nothing Auxiliary Relays ................................................................................. 25

12.8 Other Devices .......................................................................................................... 26

13 Current Transformer/Voltage Transformer Polarity and Phasing Tests ............ 26

14 Primary Injection Tests ......................................................................................... 27

14.1 General Requirements ............................................................................................ 27

14.2 Current Primary Injection of Simple Schemes .......................................................... 27

14.3 Current Primary Injection of More Complex Schemes ............................................. 28

14.4 Voltage Primary Injection ......................................................................................... 30

14.5 Voltage Primary Injection of 33kV Neutral Voltage Displacement Protection ........... 30

15 Functional Checks and DC Operations ................................................................ 31

15.1 General Requirements for Functional Testing .......................................................... 31

15.2 Tests ....................................................................................................................... 32

16 Full Load Acceptance Test ................................................................................... 33

17 Telecontrol Commissioning ................................................................................. 33

18 Final On-Load Tests .............................................................................................. 34

19 Re-commissioning after Fault Repair or Modification ........................................ 36

20 References ............................................................................................................. 37

20.1 UK Power Networks Standards ............................................................................... 37

20.2 National Standards .................................................................................................. 37

Appendix A – Diagrams .................................................................................................... 38

Appendix B – Overcurrent Relay Characteristics ........................................................... 48


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Figures

Figure A-1 – Test Circuit for CT Magnetisation Curves ....................................................... 38

Figure A-2 – CT Magnetisation Curve Example .................................................................. 39

Figure A-3 – Flick Test for CT Polarity ................................................................................ 40

Figure A-4 – CT ratio and Polarity Check by Primary Injection ............................................ 41

Figure A-5 – Typical Bias Differential and Earth Fault Protection Scheme for Yd1

Transformer (+90 Connection) ......................................................................... 42

Figure A-6 – Typical Scheme for Yd1 Transformer – Proof for Phase through Fault Stability .............................................................................................................. 43

Figure A-7 – Typical Scheme for Yd1 Transformer – Proof for Earth through Fault Stability 44

Figure A-8 – Typical Scheme for Yd1 Transformer – Simulated Internal Earth Fault (Operate) Conditions ......................................................................................... 45

Figure A-9 – Typical Scheme for Yd1 Transformer – Simulated Internal Earth Fault (Stability) Conditions ......................................................................................................... 46

Figure A-10 – CT Relay Secondary Injection Tests ............................................................. 47

Tables

Table 12-1 – Accuracy of IDMT Relays ............................................................................... 24


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1 Introduction

This document provides guidelines and preferred practices for the safe and effective testing, pre-commissioning and commissioning of electrical plant and associated protection and control equipment installed on UK Power Networks distribution networks.

This document complements, and should be read in conjunction with the references in Section 20.

2 Scope

This document provides general guidance on the aims, methods and practice of performing pre-commissioning and commissioning of the following plant and associated systems:

11kV, 33kV and 132kV transformers, switchgear, overhead lines and cables.

Current and voltage transformers associated with the above.

Protection and control systems associated with the above.

Supporting auxiliary systems associated with the above.

It is not feasible to cover every configuration of plant and equipment but the guidance and practices outlined are generic to those most likely to be encountered. Some equipment and systems, which require more specialised procedures, may be outside the scope of this document but the philosophy described within and the other referenced engineering standards, should also be applied to such systems wherever practicable. Guidance notes on such systems will be referenced where these are available.

The guidance applies to existing plant and systems as well as new plant and systems. Typically, such testing would be required following installation, maintenance, overhaul, re-location, modification or to satisfy reliability targets.

While plant inspection is not wholly a subject associated with commissioning it is considered an important aspect which should be completed before commencement of comprehensive electrical testing. This will ensure that the plant has been correctly erected and is ready to progress to the testing stage. Some typical guidance is included with respect to switchgear and transformers; more detailed inspection schedules can be found in the respective test forms.


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3 Glossary and Abbreviations

Term Definition

AVC Automatic Voltage Control

AVO Product trade name for analogue multimeter manufactured by AVO International Ltd, Dover

CT Current Transformer

E/F Earth Fault

EDS Engineering Design Standard

ENA Energy Networks Association

Fluke Digital Multimeter manufactured by Fluke Ltd

IDMT Inverse Definite Minimum Time (Relay)

IR Insulation Resistance

LEM NORMA Instrument manufactured by LEM-Norma Ltd

NVD Neutral Voltage Displacement

O/C Overcurrent

OHL Overhead Line

REF Restricted Earth Fault

RMU Ring Main Unit

SBEF Standby Earth Fault

SCADA Supervisory Control and Data Acquisition

SEF Sensitive Earth Fault

TCS Trip Circuit Supervision

VT Voltage Transformer

XLPE Cross Linked Polyethylene


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4 Co-ordination and Delegation of Commissioning Work

Reference should be made to ECP 11-0001 for the quality control, planning and programming of commissioning activities. Some general aspects in connection with commissioning activities, outlined in the following sections, augment the requirements of ECP 11-0001.

4.1 Commissioning Personnel

It is desirable that the Commissioning Engineer should remain the same throughout all commissioning activities.

Delegation of work may be necessary on larger schemes where the Commissioning Engineer may require assistance. The Commissioning Engineer's responsibility will be to co-ordinate the work and the results obtained, and should be present at all tests where special care has to be taken.

However, for smaller or one-off installations, it is accepted that the same person may have to be responsible for both construction and commissioning.

4.2 Commencement of Testing

Testing should always be carried out in a logical and efficient order at a relatively late stage in the construction work to ensure that nothing that has already been proved is disturbed by subsequent construction or testing.

4.3 Quality Control and Attention to Detail

In all situations, suitable standards should be maintained in terms of:

Care.

Co-ordination.

Completeness.

The Commissioning Engineer should make no assumptions and should not accept any circuit as proven until this has been demonstrated in both a positive and negative sense and documented in approved records. A methodical and structured approach together with awareness of what is occurring around the immediate place of testing is essential. For example, the testing process in progress on a different feeder circuit may have caused an alarm received on an apparently unrelated feeder circuit, and all such incidents should be fully investigated.

Co-ordination should include a reappraisal of existing network conditions before connecting new extensions. Any necessary revisions to the protection settings elsewhere should be made, to allow for the new plant. Any interim settings applied when setting up the new relays should be confirmed with the planning or protection engineer before the plant is finally put into service.


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4.4 Safe Working Practices

All commissioning work shall be carried out in accordance with the requirements of the Distribution Safety Rules, Health and Safety at Work Act and associated regulations using safe procedures. Network Control should be kept fully informed of progress.

Where auxiliary supplies are employed, for example, to prove control/tripping, tap changer or pumps and fans, due care shall be taken, and other personnel warned that the equipment may be LIVE.

Before the date at which high voltage plant could be made LIVE, a written energisation notice (refer to HSS 40 052) shall be issued by those responsible for making LIVE and given to all parties involved in the construction work, and a written acknowledgement obtained in reply. At this stage the work becomes subject to operational discipline and safety procedures and permit-to-work/sanction-for-test procedures shall then be adopted.

4.5 Documentary Records of Protection and Control Equipment

Before commencing testing of control and protection circuits, it is essential to fully record details of the types, ratings and serial numbers of all relays, CTs, VTs and other equipment in the scheme. This provides a check for compatibility, and allows for entry onto the asset database. Future type defects, modifications or replacements of equipment may then be identified and managed.

4.6 Recording of Test Results

The cost and effort of carrying out commissioning tests can be wasted if the results are not recorded in a consistent and usable manner. Testing during maintenance or fault finding is a follow-on to the commissioning tests, and deterioration of insulation levels, relay performance etc. can be identified by reference back to the earlier results.

Approved test forms are available which cover most usual applications are available from the Intranet. (Standard maintenance forms, generally comprising a shorter sequence of tests than those carried out at commissioning, are available separately).

The tests stated in the test forms are the minimum required to fully cover the requirements, and have been set out in a logical sequence.

Wherever practicable, the test forms are designed to cover several possible alternative schemes of a similar type. Test items should be crossed through wherever they are not applicable in a particular scheme, and any special tests required should be included under 'other tests/comments', or else additional sheets may be attached to the basic form.

After installation and commissioning activities have been completed all relevant schematic and wiring drawings shall be marked-up with any revisions necessary and copies sent to Capital Programme Delivery for modifications. The relevant protection should also be recorded and submitted. Refer to EDS 11-0001 for further details on maintaining records and 'as built' information.


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5 Inspection and Testing Order

The following generic list of tests and checks covers most equipment, and provides the recommended order in which the tests are normally performed. The order is chosen to provide as much self-checking advantage as possible. If, for instance, the current transformer circuits are to be disconnected to obtain magnetisation curves, then the primary injection tests carried out at a later stage will prove that the connections have been restored correctly. Removal or disconnection of wiring associated with previously tested circuits shall be discouraged, otherwise all testing to fully prove the disturbed circuit should be repeated.

Generic inspection and test list in recommended order of execution:

1. Inspection of the plant.

2. High voltage pressure tests of primary plant.

3. Resistance measurements.

4. Insulation tests of ac and dc control and protection circuits.

5. Secondary circuit insulation resistance.

6. CT magnetisation curves.Relay secondary injection tests.

7. CT and VT ratio and polarity tests by primary injection.Control circuit wring checks.

8. Functional tests of control, closing, tripping and protection, including Inter-tripping if provided.

9. Mechanical/electrical interlock checks.

10. Functional tests of telecontrol controls, alarms, indications and analogues.

11. CT primary injection and wiring loop resistances.

12. Back-tripping and blocking circuit tests.

13. Pre-energisation checks.

14. Post-energisation checks - on-load checks of relays and directional elements, instruments, analogues etc after making LIVE.


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6 Guidance on Measuring Instrumentation Practice

6.1 Choice and Use of Test Instruments

All test equipment used during commissioning of plant should have a current 'tested and/or calibrated' certificate. All test equipment used during a particular test should be recorded on the relevant test form.

When using a ready-made test set (such as a Megger, Ductor or Pressure Test set) including a built-in meter designed for the purpose, the integral meter may be used for measurement, subject to calibration as above.

For most routine testing jobs, an ordinary multimeter such as an 'AVO' or a 'Fluke' are acceptable. However, when using multi-purpose instruments, it is important to appreciate that different types of voltmeter, ammeter and ohmmeter work in different ways, and can give misleading readings in some situations.

The most suitable instrument available should always be chosen, depending on the measurement you want to make. For example:

'True RMS' ammeter for waveforms that are not sine waves (e.g. CT Magnetising Current).

High impedance voltmeter (e.g. Fluke, not AVO) when reading voltage in electronic equipment, so that the circuit is not loaded by the meter.

Traditional analogue ohmmeter with a battery source (AVO or similar) for continuity through electronic devices (which may not conduct below a minimum applied voltage).

'Bridge' type ohmmeter for any continuity value less than about 10 (where an AVO will be inaccurate, and some 'Flukes' may display only one or two Figures).

Ohmmeters, particularly, can give very different results depending on what current and voltage values they are using to make the test. If in doubt, check again with a different type of meter, or swap the leads over (in the case of polarity-conscious electronic devices).

Diode-resistor series circuits may be impossible to test with a normal multimeter, because of the minimum voltage that has to be applied across the diode before it will conduct. Testing by 'Ohm's Law' using a separate battery, voltmeter and ammeter will overcome this problem.

Severe oxidisation or corrosion of relay or switch contacts can cause defective operation in normal service, but even with contacts in good condition a thin surface layer may exist that requires a minimum test-voltage to break down, and a minimum test-current to produce a consistent resistance reading. Resistances of primary busbar connections or switchgear contacts need to be measured with a specially designed test-set capable of producing an adequate current output.

AC voltage measurements in high-impedance circuits isolated during testing (e.g. the VT voltage measuring input to a microprocessor directional relay) can be greatly influenced by stray voltage 'pick-up', which can occur via the inductance or capacitance of adjacent live wiring. In some cases it may be necessary to artificially load a 'disconnected' VT input circuit with an external resistor during testing, to collapse any unwanted voltage pick-up. The same type of problem can give rise to spurious voltage readings from high-impedance digital voltmeters, if the clip leads are not making proper contact. If in doubt, the reading may be rechecked with an AVO or similar.


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6.2 General Measuring Instrument Practice

Consider the effect of connecting your test meter to the circuit under test. What is the impedance of the meter? Will it disturb the values you are trying to measure?

If using more than one test meter at once in a circuit (e.g. ammeter, voltmeter), will the order they are connected in matter, e.g. is the ammeter reading the current drawn by the voltmeter as well as the load?

Always select the multimeter range switch or test-lead socket before connecting to the circuit. For accurate readings, select the meter range where the pointer is in the top half of the scale, or there are the most digits displayed.

Don't always believe a digital meter! Check that the connections are on firmly, so you don't get stray 'pick-up.' If you suspect a problem, check with an electromechanical type meter instead.

If you are trying to measure something that is varying slowly, an analogue meter (pointer-scale or bar graph) will be easier to read than a digital display.

6.3 Measuring Large Quantities

Always consider how big the reading is going to be before connecting the meter. Particularly with currents; could the current be bigger than the meter can withstand? AVOs can usually read up to 10A; some digital meters are limited to 2A.

For large currents (above about 10A) use either a clip-on ammeter, or better, use a clip-on current transformer to enable a multimeter to read higher ranges. Remember to select the right meter range, and allow for the multiplying factor in the readings.

For high voltages (above normal Mains 230/400V), readings from the network are usually taken off the protection or metering voltage transformers, assuming the VT ratio to be exact. For special injection testing (e.g. high knee-point-voltage CTs) then range extenders are available for AVO or similar meters.

6.4 Safety Precautions when using Instruments

Always connect the 'earthy' lead first, and disconnect it last.

When using a switch or plug-selected multimeter, always start on the highest range. Never change Range while the meter is connected (some modern digital meters can do this automatically).

When taking 'split-plug' readings of CT current on-load from a protection relay or test block, ensure that the meter is on the correct ampere range and that the split-plug, leads, and connections to the meter are all in good order. Open circuited CTs are dangerous!

When using current or voltage injection from a portable test set or Variac, remember that one side of the output may be LIVE, and its 'earthy' side may be connected to mains Neutral. If using any special mains powered instrument in a metal case (such as an oscilloscope) remember that one side of its input leads will probably be connected to earth.


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7 Inspection of Plant

On acceptance of the equipment from the construction engineer, the equipment should be inspected for damage and for conformity to the scheme details, e.g. equipment type, ratings. The equipment should have been inspected for conformance to the Equipment Specification for its type, and if this evidence is not available from the construction stage, then the inspection shall be carried out at the commissioning stage.

It may be convenient to delegate some items of inspection to the engineer supervising construction, providing confirmation is obtained and recorded. For example, some wiring items, components and busbars are inaccessible after they are boxed-in, and limited pre-commissioning (e.g. Ductor tests) may be required at the construction stage.

Some general guidance is given in the following sections. For full checklist, reference should be made to the appropriate test form.

7.1 Switchgear and Conductors

Check for filling medium quantity, SF6 gas pressure (or oil level) as appropriate, in the circuit breaker and voltage transformer tanks etc. Where the equipment is fitted with gas pressure switches, or lock in/out device, the Contractor installing the equipment shall have proved the correct operation.

When inspecting switchgear, particular attention shall be paid to the cleanliness of all spouts or bushings which may be inaccessible after the gear has been made LIVE. Solid insulation should be cleaned with dry lint-free wipes.

Ensure that all switchgear frame earthing and bonding connections are correctly in place and the connections tight.

While disconnected from the system, operate the switchgear to all positions. At each position, also check locking points for application of operational and/or safety locks, and correct function. Check mechanical interlocks in all positions. Prove mechanical and electrical position indicators for correct operation and legend. Ensure all panels and covers are correctly refitted before energisation

Ensure that all equipment labels, both primary and panel, are in place and correct.

Any apparent defect that is discovered on one switch or panel should be thoroughly investigated on all other similar items in the switchboard, and where appropriate reported to Asset Management .

7.1.1 Resistance Measurements

Perform contact resistance measurements, using a test instrument capable of passing 10A test-current, to prove contact integrity at all points. The testing shall include:

1. All site assembled busbar joints.

2. Contact resistance of all circuit breakers and disconnectors.

3. All joints in phase conductors.

4. All joints in earthing conductors.


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Item 1 should be checked immediately after the joint is made and before replacing covers in the case of metal clad switchboards. After switchboards are completely assembled this test should also be performed by measuring between cable box connection of adjacent panel. Inconsistent results shall be investigated, rectified and retested.

For item 3 and 4 the resistance shall not be less than an un-jointed section of conductor.

7.2 Distribution Transformers

Ensure that all earthing and bonding connections are correctly in place and the connections tight.

Ensure that the oil drain valve is closed, and the drain-plug in place. Inspect for signs of oil leakage, especially around bolt-on type radiators, and switchgear/cable box flanges.

Check the transformer oil level is visible in the sight glass, allowing for the ambient temperature. The level should correspond to the marked 15°C point.

Ensure the transit cap has been removed from the breather pipe. (In rare instances, a dryer may be fitted, check or fill with dry silica gel as applicable).

Check free movement of the tap change handle, set to required position (1 - 5, nominally position 2 or +2.5% HV volts). With system voltage applied to the primary side, check open circuit secondary voltage (250/433V ± 1.25%, or as noted in the project file) and adjust if necessary.

Prove phase rotation, and phase-in with adjacent low voltage network.

Note: Any change of tapping position is to be made with the transformer dead only.

7.3 Primary System Transformers

Ensure that all frame earthing and bonding connections are correctly in place and the connections tight.

Check the conservator oil level is visible in the sight glass, allowing for the ambient temperature.

Sample and test the oil.

The level should correspond to the marked 15°C point. Inspect for signs of oil leakage, especially around bolted connections and bushing/cable box flanges.

Carry out functional and secondary wiring tests, on all control circuits, e.g. pumps and fans, oil and winding temperature devices, voltage control, and Buchholz (oil and gas operated) relay. Follow the basic procedures described in Section 9 onwards as applicable.

Carry out functional tests on voltage control system, pumps and fans etc. Ensure the pump filters are fitted correctly, and the pump flow direction is correct.

Operate Buchholz alarm and trip by injection of air (where possible), and prove operation of panel alarm and trip flag relays.


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Verify accuracy of winding and oil temperature devices by secondary injection and suitable simulation.

Perform voltage testing to establish transformer winding connections (vector group).

Verify on-load tap changer operation from all locations (local, remote and telecontrol, if applicable) and also on automatic. Verify correct operation and voltage ratio with three phase test voltages over full range. Ensure there is no break in continuity through each three poles of the tap changer across its entire tapping range. This check should be performed using an analogue1 (AVO) meter setup to measure the magnetising current of each winding using a 400/230VAC test voltage. Any short break in magnetising current during a tap operation can be seen readily using an analogue meter. Verify any parallel running tap change controls. Perform secondary injection to automatic tap changing relays to verify operations at preferred settings.

1 The response time of a digital (fluke) meter is not fast enough to ensure any short breaks in tap changer continuity are seen during the tests.


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8 High Voltage Pressure (Dielectric) Testing

All high voltage plant shall be tested 'to confirm' its ability to withstand full system voltage, and to identify any incipient breakdown of insulation. This section outlines the criteria for the on-site insulation testing of cables, switchgear and transformers.

Insulation tests shall be carried out before any new, modified or repaired equipment is energised from the power network. Before re-commissioning cables or plant that has been de-energised for an extended period of time, but has not been worked upon, a risk assessment shall be made to decide if insulation testing is required. This assessment shall take into account factors such as the activity of third parties in the vicinity of the cable or plant.

The purpose of site insulation testing is to demonstrate that cable and plant can be safely connected to the system. On-site insulation testing is also required to ensure that UK Power Networks complies with its statutory duties under current legislation.

Insulation testing of overhead lines is not considered practical. Therefore, before commissioning, a visual inspection shall be made of new lines and the modified parts of previously energised lines. Before re-commissioning overhead lines that have been de-energised for an extended period of time, a risk assessment shall be made to decide if a visual inspection is required and to decide on the best course of action before returning to service. This assessment shall take into account factors, such as the activity of third parties in the vicinity of the circuit or severe weather conditions.

All equipment shall pass an insulation resistance test before and after any high voltage dielectric tests.

A record of all tests shall be made on the approved test form.

The ac and/or dc pressure test values which shall be applied to both old and new plant shall be in accordance ECP 11-0006.


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9 Wiring Insulation Resistance Tests

9.1 Circuits to be Tested

Insulation resistance tests are to be carried out on all ac and dc protection, control, alarm and indication circuits to ensure that wiring is in satisfactory condition before the circuit is put into service.

It is desirable to measure the insulation of all circuits before proceeding with other tests, and it is essential that all ac and dc wiring associated with protective gear is proved, relay contacts and auxiliary contacts, etc being closed as necessary, to ensure this.

When carrying out insulation resistance tests on secondary wiring it is advantageous to earth all other associated secondary circuits other than the circuit under test. This approach provides the additional benefit of detecting any inadvertent connection between circuits indicating a wiring error. Also, this enhances the insulation resistance test because all wiring on the other circuits will be at earth potential rather than floating. Therefore, any insulation damage between loomed secondary wiring will be more readily identified in the readings obtained. The following tests should be carried out:

Insulation resistance of current transformer circuits.

Insulation resistance of voltage transformer circuits.

Insulation resistance of dc circuits.

Insulation resistance between CT and VT circuits.

Insulation resistance between dc and VT circuits.

Insulation resistance between dc and CT circuits.

When measuring the insulation resistance to earth of an individual circuit, all the other circuits should be normal, e.g. earth links closed and dc circuits normal. This will ensure that the insulation of this circuit is satisfactory, both to earth and to all other circuits. It should be noted that in some installations the battery may run 'un-earthed' and its insulation-to-earth may not be monitored by a 'battery earth fault' alarm relay, with centre-point earthed through a high resistance to the dc wiring measured. Therefore a complete insulation test of an individual circuit to earth and relative to battery circuit wiring will not be obtainable unless arrangements are made to temporarily earth the battery via a high resistance, e.g. AVO, during testing.

Bus-wiring insulation should be checked between wires, and between each wire and earth. It is particularly important in the case of circuits connected to the protection battery that there are no 'sneak circuits' between positive and negative, or between positive and the trip wiring, which could cause mal-operation or battery failure.

Individual circuits, such as TRIP, CLOSE, and ALARM, should be tested to earth and between poles before fuses and links are inserted.

At this stage fuses and links can also be checked for size, rating, and function.

Inspection of the schematic diagrams will best show how switch wires and other parts of a circuit, such as operating coils and contactors, may be included in the test and not overlooked. It may be necessary to repeat the tests a number of times with switches or relays in different positions or operating states. Insulation tests across open contacts of panel switches and plant/equipment auxiliary contacts shall also be carried out to prove a sufficient gap exists between the contacts.


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9.2 Precautions

Before carrying out any insulation resistance test using applied voltage, care shall be taken to ensure that any electronic relays and telecommunications equipment are either disconnected or protected against over-voltage damage, which can be costly. Floating battery chargers should be considered in this category.

Modular type electronic relays can usually be withdrawn from their cases during insulation testing, if necessary, but care shall be taken not to damage the electronic components inadvertently through 'static' discharge. To guard against this, always observe anti-static precautions when withdrawing or replacing a relay module from its case.

Before withdrawing the relay, first 'earth' yourself by touching the relay case or panel metalwork, and then put the withdrawn relay module down onto a conducting surface that you have touched beforehand. Do not shuffle your feet during this process because more static electricity can be introduced dependent on the footware being worn. If using a earthing wristband ensure it has a one megaohm resistor fitted between the wristband and earth. This reduces the risk of increasing the current that could potentially travel through the chest if a live part is inadvertently touched with the other hand whilst wearing the anti-static wristband.

9.3 Test Voltage and Results

1000V dc is the preferred test voltage. A Megger tester or a test set that can provide alternative output voltages and currents.

The values of insulation resistance to be expected cannot be predicted. They may vary in

practice from tens of thousands of megaohms down to say 0.2M, depending on humidity and whether plant has been stored etc. Humidity in new substation buildings is often very high.

All test values should be recorded and low tests (e.g. less than 1 M) should be investigated and rechecked at the earliest opportunity. A retest may prove that the low readings were not due to an incipient fault. Where low readings are obtained on wiring located within outside compounds the reason for this can often be due to tracking occurring at the points where the wiring is terminated and not necessarily the multi-core cables themselves. The tracking can result though an accumulation of damp grime that has become deposited in termination boxes and marshalling cabinets over a long period of time. Dirty terminations shall be cleaned using an approved cleaning spray intended specifically for this purpose while ensuring compliance with the safety measures identified on the COSHH sheet for the product.

9.4 CT Secondary Circuits

CT secondary ac circuits should be tested to Earth with the star-point earth link removed (this should never be done unless the primary circuit is dead). A second test should be made to prove that the replaced earth link is effective.


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10 Loop Resistance Tests

10.1 Current Transformer Secondary Circuits

Loop resistance measurements are to be made on all CT secondary circuits.

Those associated with circulating-current type protection are necessary to establish the operating characteristics of the protective scheme, and should be checked against the Manufacturer's calculated Figures. Separate values are required for CT and lead burdens, and all measurements are to be recorded on a lead-resistance diagram (refer to the appropriate test form for the format of recording results).

The loop resistance of each CT secondary circuit should be measured with a multimeter having a low resistance measuring resolution of no greater than 0.1 ohms. Insulating plugs may be inserted in the plug-bridge or test-plug block of the protection relays, so that the relay input windings are not included in the test.

The test should measure the resistive burden of the CT secondary winding plus the phase wiring from the relay panel.

The burden of the relay is not included at this stage as it may vary depending upon relay type, setting, saturation etc.

Where the total burden of the circuit is required for the assessment of CT performance, typical values for the relays may be added to the CT loop value for calculation purposes.

Any variation in resistance between phases should be investigated and explained by the presence of ammeters, metering etc. Loose wire connections show up at this stage by giving abnormally high, or varying, readings.

10.2 Pilot Wires

Pilot impedance and phase angle measurement of rented British Telecom pilots is necessary when these pilots are to be used with unit type protection (not intertripping or acceleration etc). When necessary the same measurements shall be made on private pilot cables.

10.3 Other Circuits

Within the limitations of the design of the switchgear the loop resistance of trip coils, closing coils and contactors etc should also be measured where practical from the supply fuse and link, with the appropriate function set up.

The test will show that the coils etc are of the correct value and are wired correctly with no short circuits.

The recorded value of loop resistance can be of use during maintenance. For example, circuit breaker auxiliary switches in a reclose circuit may deteriorate through oxidisation where they are left open for extended periods with the circuit breaker normally closed. This condition would show up as an increase in the loop resistance, and action could be taken to prevent mal-operation.


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11 Current Transformer Magnetisation Curves

The importance of adequate CT magnetisation characteristics in relation to protective schemes shall always be stressed. During commissioning, the magnetisation curves of CTs are checked to:

Prove that the CT is healthy and without shorted turns.

Provide an initial record of the characteristic, from which the 'knee point' and saturation values can be obtained to assess protection performance.

Prove in the case of Neutral CTs (e.g. in REF and SBEF schemes) that fortuitous earth loops are not present at insulated cable glands etc.

Prove that the characteristic of a CT matches the function of the circuit to which it is connected.

It is essential that:

Existing or re-used CTs, or new CTs without Manufacturer's curves, should be tested up to and beyond the knee-point, and where practicable up to a maximum saturated magnetising current of (typically) 1A, for which the applied voltage should be recorded.

The magnetisation characteristic of all new Current Transformers is to be checked at the minimum number of points necessary to identify the CT with reference to the Manufacturer's estimated design curve, and to determine the suitability of the CT for its intended duty.

Because a CT is built around an iron core, the relation between voltage and magnetising current is nonlinear, and harmonic distortion will be always present in the voltage or current waveforms. By plotting the terminal voltage of a CT against the magnetising current in discrete steps, a magnetisation curve will be obtained which will approximate to the hysteresis loop for the iron.

It is usual to record the CT 'mag curve' as a table of results, rather than plotting the actual curve on graph paper each time. If it is required to find the exact 'knee point' for the CT, then the curve can be sketched out as necessary later (e.g. see Figure A-2). The 'knee-point' is defined as the position on the curve where a 10% further increase in voltage results in a 50% increase in current drawn.

Typically at least 8 or 10 points should be taken on the curve, starting by raising the applied voltage in moderate steps, and then in smaller steps once the current drawn begins to increase rapidly as the knee-point is reached and saturation approaches.

The knee-point is normally reached before the magnetising current exceeds 20% of the CT rating. The slope of the curve depends on the quality of the iron core. A CT having a high-quality iron or mu-metal core may saturate at a very much lower magnetisation current.

Because the repeatability of the curves will be affected by remnant magnetism in the iron core, the readings will depend on whether the current is rising or falling. For consistent results, it is first necessary to de-magnetise the CT and to plot the magnetisation curve for currents increasing from zero. De-magnetisation can be achieved by raising the injected current briefly to fully saturate the iron core, and then reducing the current smoothly to zero by turning down the Variac/Test Set control (and not by switching off suddenly). This procedure takes the iron core through progressively smaller hysteresis loops, until finally the current is zero and there is no magnetism left.


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Figure A-1 shows a common test circuit. The isolating transformer, if used, prevents the supply neutral Earth from influencing the test, and avoids the need to lift the CT star-point earth link. Alternatively the integral variable ac Voltage output on a secondary injection test set can provide a convenient test supply.

Both the Variac and the isolating transformer (if used) should only be operated up to 50% of their nominal ratings, to ensure that they do not influence the readings by causing waveform distortion.

The voltage applied to the CT is sinusoidal and therefore a rectifier-moving coil type instrument such as an AVO meter, or a basic Fluke, can be used without errors.

The current waveform drawn by the CT is distorted by the harmonic current, and strictly speaking a moving-iron or 'true RMS' type meter should be used to record the magnetising current.

Other methods of taking magnetisation curves by using a fixed voltage and a variable resistance can give an optimistic result, and the CT may appear better than it is.

Magnetisation curves can be taken after the CT Primary circuit has been jointed, provided that earths do not exist on both sides to create a current loop or 'shorted turn'. This occurrence can be identified by a lower, flatter curve (more current being drawn for the same applied voltage) than expected.

On large schemes a number of CTs performing different functions may be fitted in one circuit breaker. For example:

Overcurrent and earth fault protection, restricted earth fault protection.

Unit protection.

Ammeter and instruments, metering.

AVC.

Fault recorder etc.

The Metering and Instrument CTs are usually designed to saturate at a much lower voltage value than say the REF CTs, to give protection to the instruments under fault conditions.

Although the ratios of protection and instrument/metering CTs may be the same, to install them transposed would result in possible mal-operation of protection on the one hand and damage to instruments on the other. It is therefore essential to positively identify CT type with application.


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12 Secondary Injection and Protection Relay Tests

12.1 Secondary Injection Applied to Current Operated Measuring Relays

Relays are essential building blocks that make up protective systems. In all cases, all designs of relay shall be given a minimum amount of testing after connection, to prove their function and settings.

These tests should show up any handling or installation faults that may have occurred since manufacture, and are also intended:

To check that the relay has not been damaged in transit.

To check the relay against its specification.

To check the relay as part of a complete scheme.

In the case of a user-programmable electronic relay, to confirm that the correct software 'configuration and logic' files have been installed and proven to the intended scheme design.

The electrical tests should be preceded by a thorough visual inspection, when any packing material is removed and the relay is made ready for operation. In the case of an electromechanical IDMT relay for instance, it is possible for swarf to be attracted to the disc and brake magnets. So the full travel of the disc should be checked and smooth operation observed.

AC secondary injection tests are carried out with the dc tripping fuse and links removed and with the tripping contacts connected to a time interval meter (see Figure A-10). If the relay is an electronic type requiring a permanent auxiliary supply, then the alarm/auxiliary supply fuse and link will need to be left in, or an external supply injected to power the relay.

When setting-up the ac test set, it is important (particularly with electronic relays) to ensure that the injected current through the test ammeter and relay is an undistorted sine wave, otherwise apparent current setting and timing errors will occur. As a general rule, always use the lowest-current (highest-voltage) output range or terminal selection on the test set that is compatible with the required test current, and if the current is then difficult to control, add a series resistance, or a filter unit, to the circuit.

During test procedures, wiring should be disturbed as little as possible, and where modern high quality CTs are fitted then the relay test current may be injected at a convenient terminal block in the relay panel, or at the scheme test block if fitted. Although the CTs will be in parallel with the relay coils during the secondary injection, their magnetising current will be negligibly small compared with the relay test current. There shall be no short-circuit across any CT primary (e.g. via earths on both sides) otherwise significant current will be shunted through the CT secondary.

Where several relays exist on one panel and are powered by the same CT secondary circuit, take care that the test current does not flow through relays in series so as to exceed their rating. Vulnerable relay elements should be shorted out during such testing.


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All relays are to be examined, care being taken before opening relay cases to ensure that no foreign matter can fall inside. Note is to be taken, where applicable, of the following points:

Relay mechanical movement is free.

Magnet gap and induction disc are clean.

Gear teeth are clean.

Contacts are clean and have adequate wipe.

All contacts make simultaneously, or in a preferred order.

Contacts make when time multiplier setting is zero.

Resetting times are within limits.

Flag mechanism operates in correct sequence with respect to contacts.

Flag, indication and contact-reset knobs/buttons operate with relay cover on.

Relay cover glass and gasket provide effective seal.

Labelling and phase colours are correct.

CT shorting and dc isolating contacts or switches in withdrawable relay cases operate satisfactorily.

12.2 IDMT Relay Operation and Timing Tests

It is usual to commence testing a relay having an IDMT type characteristic using a plug setting of 100%, to provide a convenient range of test currents, and a time multiplier setting of 1.0 to give full disc travel (if electromechanical) and a convenient operating time.

It is only necessary to check the shape of the IDMT curve at this one current setting, since the other settings are simply related by the number of turns on the coil, or in the case of an electronic relay, by scaling resistors or by multiplying factors in the software. It is good practice to also inject the relay at its intended final in-service setting, when known, and confirm that sample current/time values are as expected. A final timing test at setting can be carried out at twice and four times the plug/base setting. For the usual standard inverse characteristic, the relay operating times should be ten times and five times the applied time multiplier respectively. Testing at two points on the inverse/time curve then proves the relay is operating to the correct standard inverse characteristic.

A fault in the relay input coil will show up on all settings under ac injection test conditions.

Electrical timing tests should be carried out to prove the shape of the IDMT curve at convenient points. The definition of the characteristic and the limits for errors are given in IEC 60255 Part 3.

There are four curve characteristics normally encountered for IDMT relay and these are:

Normal inverse.

Very inverse.

Extremely inverse.

Long time.

The formula defining the first three of these curves is derived from BS EN 60255 Part 3 and times deduced for each characteristic are shown in Appendix B.


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12.3 IDMT Timing Accuracy

12.3.1 Start Timing Function

IDMT relays can be tested for 'creep' by slowly increasing the test current up to the setting value. At the relay setting current, the disc should be stable and not move, or for an electronic relay the 'I > Is' or equivalent indication should not show.

The disc should commence turning, or the 'I > Is' indication should pick up at above the setting current but not greater than 1.3 times the current setting. In electromagnetic relays, at this point operating torque just balances friction and other restraint forces. Any undue restraint, such as bearing friction, will cause operation to occur at a larger current.

For 'long time earth fault' elements the minimum operating current should not exceed 110% of the relay setting and the timing function should not start at a current equal to or less than 75% of the relay setting.

12.3.2 Electromagnetic Relay

At the highest time multiplier setting, and at a current setting of 100% for relays with a 50%-200% range, 40% for relays with a 20%-80% range, and 25% for relays with a 10%-40% range, the operating time limits of electromechanical induction disc relays are shown in the following table:

Table 12-1 – Accuracy of IDMT Relays

Time Multiplier (TM)

Reference Plug Setting Multiple of Current (PSM)

Acceptable Limit On Normal Operating Inverse Time-lag Elements

50-200% Range

20- 80% Range

10-40% Range

Normal Inverse

Very Inverse

Extremely Inverse

Long Time Earth Fault

1.0 100% 40% 25% 2

±16.7%

(i.e. 8.3 - 11.7s)

±17.6% ±18.3% ± 17.6%

1.0 100% 40% 25% 4

± 9.7%

(i.e. 4.5 - 5.5s)

±11.5% ±14.0% ± 11.5%

Timing range acceptable is given, by way of example, for the normal inverse characteristic. Other times may be obtained using the values derived in B.

12.3.3 Electronic Relays

Electronic relays may be expected to operate within a narrower tolerance range than mechanical relays. However some designs are more sensitive to non-sinusoidal waveforms and a current filter unit may be required to obtain credible results. 'True RMS' ammeters should be used for preference when testing electronic ac measuring relays.


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12.4 Instantaneous Relays

Where applicable the operate and reset values for attracted armature relays are to be taken at the design setting only.

Instantaneous (high-set) relay elements should be tested for current pickup and current drop-off, and the values compared with the current setting. Take care to set up the current value quickly and apply it to the relay for the minimum time to operate; otherwise the thermal rating of the relay input coil may easily be exceeded.

Certain modern electronic relays have such wide 'instantaneous' setting ranges that, at high settings, even the quickest conventional pick-up/drop-off test may overheat the relay input module. In these cases the manufacturers recommend a different procedure, in which a current level near to but less than the relay setting is first set up on the test set, with the relay shorted or out-of-circuit. This pre-set value of current is then suddenly applied to the relay and switched off again quickly whether the relay trips or not. By gradually increasing the pre-set current value, a sequence of readings is obtained where at some point the highest 'current not to trip' and then the lowest 'current to trip' are recorded. If the mid-point between these readings corresponds reasonably to the setting, bearing in mind the expected pick-up/drop-off tolerance, then the result is acceptable.

12.5 Complex Protection Relays

Relays which have other more complex characteristics or employ watt-metric type measuring principles, e.g. bias differential relays, directional/distance relays, should be tested in accordance with the Manufacturer's recommendations and the approved test forms.

12.6 Voltage Operated Relays in High Impedance Schemes

For circulating current protection employing high impedance voltage operated relays the points of injection for relay voltage setting tests should be across the relay and stabilising resistance. The fault setting for this type of protection is to be established by secondary injection where it is impracticable to ascertain its value by primary injection. Injection is to be made across the appropriate relay buswires with all associated relays, setting resistors, and CTs connected. During the final primary injection tests to prove CT group alignment, measurement of the relay operating current can be correlated against the maximum practically achievable primary current. An extrapolation can then be made between the injected primary current and relay operating current to ascertain that the secondary relay current required for operation correlates with the required primary operating current.

12.7 All or nothing Auxiliary Relays

Refer to Section 15.2.


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12.8 Other Devices

Other complex control and non-electrical protection devices shall also be secondary injected and functionally checked (as described in Section 15) to prove satisfactory operation at the desired setting before use on the LIVE system.

These shall include (the list may not be exhaustive):

Transformer winding and oil temperature protection.

Buchholz relays.

Pressure relief devices.

Transformer automatic voltage schemes.

Check synchronising relays.

Automatic synchronising relays.

Auto-reclosing relays and schemes.

Trip relay resetting schemes.

Automatic isolation and reclosing schemes.

13 Current Transformer/Voltage Transformer Polarity and Phasing Tests

To verify that CT primary and secondary markings are correct and accord with the drawings, it is necessary to check each CT separately for polarity as shown in Figure A-3 ('flick' test).

The battery shown may be a 6V hand lamp type with the positive connected to the equivalent of P1 on the primary of the CT.

The meter should ideally be a centre-zero moving-coil type, but it can be an AVO used on a dc mA range.

The positive of the meter is connected to the equivalent of S1 on the secondary of the CT.

The test is based upon the fact that the induced EMF across each winding is always in the direction of the same sequence of numbers at the same instant.

Upon making the primary circuit, a positive kick should be obtained on the meter, and a negative kick when the primary circuit is broken again. Correct connection of each CT phase colour to its secondary wiring will be established visually and electrically during this test.

For VTs, although the HV star-point may not be accessible, the corresponding phasing test may conveniently be performed by applying 240V ac mains across each pair of primary phases in turn and measuring the resulting secondary output voltages. (Note: That the 'star' voltages will be unbalanced under these conditions, because the magnetising characteristics of each winding will not be identical and the neutral point is floating.


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14 Primary Injection Tests

14.1 General Requirements

Primary Injection testing of CTs can verify:

Correct CT ratio.

Correct location of CT.

Correct polarity of CTs in a 3-phase group.

Correct polarity in relation to other sets of CTs forming a unit protection scheme.

Correct wiring from CT chamber to relays.

Fault settings.

Position of ammeter in circuit etc.

Proof that previously disconnected secondary wiring has been restored.

For current primary injection, tests are to be carried out using, where necessary, equipment of up to 20kVA output. In most cases equipment of 5kVA output will suffice. In those cases where primary injection equipment of over 5kVA output is required by a Contractor, and suitable UK Power Networks owned equipment is readily available, such equipment may be loaned to the Contractor for the duration of specific test programmes, at the discretion of the Commissioning Engineer.

14.2 Current Primary Injection of Simple Schemes

Such tests are best made when all current-operated relays are connected on their panels and any pilot connections are made, but before cables are jointed to the cable boxes.

Where dual-ratio CTs are installed, a visual check should be made that they are connected to the desired ratio before setting up the test connections as shown in Figure A-4.

In the case of circuit breakers with integral earthing to ENA TS 41-36, the primary current circuit through the CTs can be made with the circuit breaker closed in the circuit earth position, and test connections made to the rear cable box. Fixed pattern switchgear will usually have a cable test connection available that can often be used for conducting primary injection tests. However, the CT position in relation to the test point varies between manufacturer’s and switchgear types and the internal single line diagram will be required beforehand to plan the primary injection tests.

In other cases the current loop can be completed at the feeder spouts, by using authorised earthing arrangements.

It is essential that all Primary Injection test leads are of heavy-duty cable and make good connections to the primary conductors, since only a limited output voltage (and power) is available from the test set, and so minimum circuit resistance is essential to obtain full values of injected current.

Before testing, any sensitive relays should be protected by shorting them with a clip lead. The test current will be flowing for longer periods than fault current, which is interrupted by the circuit breaker. Thermal ratings of relay coils shall be considered.

A typical suitable value for the injected primary current is half the CT nominal rating, as this will not give excessive secondary current if CTs are incorrectly wired, as may be possible where balanced schemes or dual-ratio CTs are fitted.


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The current in the secondary circuit can be measured using an AVO or Fluke set to ac Amps and connected to a split-plug designed to fit the plug-bridge of electromechanical relays or to fit the scheme test block of electronic relays.

The secondary current obtained can be compared with the expected value, considering the primary current injected and the CT ratio as well as the effect of any interposing CTs.

This test will also show that the secondary wiring is connected to the correct relay phase elements.

With the test connections shown in Figure A-4, the grouping of the CTs with respect to their polarities can also be checked, as can the residual or earth-fault connections.

The first test is made with primary current flowing into the red phase CT and out of the yellow, to balance red against yellow.

Only a small spill current, or ideally none at all, will be measured in the earth fault element if the CTs match. Normally, secondary current will be measured in the red and yellow CTs and a reading obtained on the Ammeter if it is connected in either of these phases.

The test is then repeated with the blue phase CT and the yellow connected to balance blue against yellow. If the results compare, then it can be assumed that red will also balance blue correctly, and a third test is not essential. However it is good practice to carry out the third test, red against blue, to prove that there has been no error.

A further test is required, using single phase injection only, to show that current can flow in the residual circuit and that the wiring is not open circuit. For this, the primary test current is circulated through the yellow CT only to earth or to the current loop at the spouts.

For a dead switchboard having several panels it may be convenient to set up the testing transformer at one end of the circuit breakers.

With the circuit breakers closed in service, it may be convenient to transfer the loop connections to each of the circuit breakers in turn. Thus, the whole switchboard can be checked with the minimum of effort and current passed through the bus bars and bus sections.

14.3 Current Primary Injection of More Complex Schemes

The primary injection principle depicted in Figure A-4 are sufficient to fully prove simple schemes such as those involving one set of CTs connected to a particular burden (e.g. an overcurrent/earth fault relay, ammeters, meters and the like).

For protection schemes involving more than one set of CTs the primary injection is a little more involved. For example, schemes for transformer differential protection, busbar protection and restricted earth protection employ several sets of CTs forming a balanced set. Under load or ‘through fault’ conditions the output of the CTs match in polarity and magnitude and circulate current between themselves such that no current passes through the relay. For internal fault conditions the output of one or more sets of CTs is not present or is present with a changed polarity. The phasor sum of secondary currents for all CTs is therefore not zero and current is forced though the protection relay to initiate tripping.

The testing principles applicable to each CT or each set of CTs associated with such schemes are the same as that described in Section 14.2, but additional primary injection is also required to compare each set of CTs with all others which form the balanced combination.


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It is not practicable to detail the precise methods to be used for performing CT ratio, polarity, and balance tests, since the method adopted for a particular installation will depend upon the location of the CTs and their manner of interconnection, and, where applicable, upon the impedance of any associated transformers. The primary injection methods employed for a particular installation are therefore to be agreed with the Commissioning Engineer.

Primary injection testing of more complex schemes should include the following:

An examination of the ac schematic diagram to verify it is correctly drawn and CT ratios (main and interposing CTs) give current balance on through faults (phase and earth) and correct relay operation on internal faults (fed from either/both sides if this is feasible). Refer to Figure A-5 for an example of a unit protection scheme; stability conditions are demonstrated in Figure A-6 and Figure A-7.

Ratio and polarity tests for each set of CTs. Recording values at the relaying point as described in Section 14.2 above. With schemes involving interposing CTs or CTs used to allow for primary transformer vector relationships the current measured can differ in value depending on the point in the scheme the measurement is taken. For example a single phase injection into a set of CTs used to support a transformer differential protection relay may result in currents in all three phases of operate and bias coils of the protection relay (Figure A-8). It is important to know what to expect with such schemes for each test configuration applied. It is essential that the expected CT secondary current magnitudes and directions are marked up on a sketch of the scheme and this detail transferred to the test record for confirmation as the test proceeds. Any deviations between measured and expected results will then be immediately revealed.

Comparison primary injection tests between one phase (nominally the red phase) of one set of CTs and the corresponding phase of each other set(s) of CTs. Each three phase set of CTs has been verified for polarity and ratio therefore it is only necessary to compare one phase of each of the separate sets of CTs, to the same point is the scheme at which the secondary injection currents were applied (usually the test block or relay). Where there is significant impedance between sets of CTs for the balanced scheme, e.g. transformer differential protection, comparison primary injection may be more easily performed using a suitable three phase or single phase voltage supply with transformer windings short circuited. It is desirable to simulate both operate and stability conditions for such schemes and as operate conditions may require the temporary removal of primary or other connections, it should be completed first. Preforming the operate shot first for each test arrangement also proves that the relay operates for the simulated ‘in zone’ fault condition. Therefore, when carrying out the ‘stability shot’ a non-operation of the previously tested relay provides the proof that the overall correct CT alignment has been achieved. All connections to be restored to normal to perform the final stability test (e.g. refer to Figure A-8 and Figure A-9).

Fault setting tests to establish, where practicable, the values of current necessary to produce operation of the relays. If not practicable these tests are to be carried out by secondary injection (see Section 12.6). A check should also be made between the actual primary test current applied and the secondary current through a current operated relay or voltage across a voltage operated relay. This check should establish that if the primary current were to increase to the desired primary operating point, then the corresponding relay operating current or voltage will be at the correct magnitude for operation, as proven during the secondary injection testing of the said relay.


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14.4 Voltage Primary Injection

Primary injection of VTs is usually carried out by applying normal 240V mains to the primary and checking the small secondary voltage(s) resulting. This is usually restricted to 11kV connected VTs, higher voltage VTs (33kV to 132kV) are checked using full system voltage and checked (phased out) against a similar in-service VT.

Full high voltage primary injection is usually restricted to 33kV neutral point displacement condenser cones, and other special cases.

14.5 Voltage Primary Injection of 33kV Neutral Voltage Displacement Protection

To calibrate 33kV Neutral Voltage Displacement (NVD) protection is necessary to apply a 50Hz high voltage to the condenser cones or capacitive bushings.

Condenser cones can be three phase types connected in star, or a single neutral connected unit depending on the method of application. Provisions are made for routinely testing the unit by applying a relatively low voltage to the coupling unit (a larger capacitor forming effectively a capacitor potential divider) at the earthy end of the NVD cones. However in order to calibrate the protection a voltage approximating to system phase voltage has to be applied to the system end of the condenser cones.

The test voltage is normally applied as a variable value up to 20kV. Precautions should be taken to ensure that the earthy end of the cones are properly connected to the coupling unit which is correctly earthed. Without an earth at the bottom of the condenser cones (directly or via the coupling unit), the test voltage will appear at the lower end of the condenser cones. The same condition would occur if the wire breaks between the star point (or earthy end) of the condenser cones and coupling unit under NVD conditions - a high voltage will appear at the star point and up to the broken wire end. To avoid this a surge suppressor is fitting to clamp any over-voltage to safe levels. Notwithstanding the surge suppressor such circuits should assumed to be a high voltage source (similar to pilot cables which can generated longitudinal voltages, and voltages appearing from open circuit CTs).

In some instances the condenser cones are replaced with capacitive bushings and a reduced voltage is necessary (approx. a third of the star connected condenser cones calibration voltage). Where capacitive bushings are provided it will be necessary to conduct the high voltage test prior to the connection of the HV cables to the bushings because the high voltage test set is unable to provide the standing cable charging current at the required test voltage.

Under these conditions the same precautions should be taken of possible high voltage output. The other (LV) winding should we earthed during such tests.

The tests are detailed on the approved test procedure and test form.


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15 Functional Checks and DC Operations

15.1 General Requirements for Functional Testing

Having dealt with the protection and control building blocks separately, it follows that their functions shall now be checked with respect to the complete scheme.

The approach to this aspect of testing is important, if faults are to be found and damage avoided.

The heavy hand that puts in links and presses buttons without progressing methodically in steps will soon run into trouble. Inspection of the schematic diagrams with knowledge of what is required from the circuits will best show how the function of each element can be checked.

A logical running order may be:

1. Mechanical checks.

2. Manual operation.

3. Local electrical operation (not telecontrol).

4. Automatic operation, where it applies.

5. Telecontrol operation.

It will be obvious for instance that the closing shall be completed before a circuit breaker can be tripped.

Telecontrol, standby and local operation shall be checked independently, with local operation first.

Non-operation of a control facility when not selected shall also be proved (the negative part of the test).

It often helps to start on simple circuits first, such as control and alarm, before going on to complicated sections of a scheme.

Ticking each contact and coil on the schematic drawing as its duty is checked will also help to ensure that nothing is overlooked.

Attention should be given to any special testing requirements such as checking circuit breaker closing at 80% and tripping at 70% (or 50%) of battery voltage.

Where trip circuit supervision (TCS) is fitted, the small monitoring current through the Trip Coil should be measured both with the breaker closed and then open. Checks should also be implemented to ensure that the current though the trip coil is within expected limits when various elements of the TCS scheme are short circuited.

It may also be necessary to check the timing of certain auxiliary switch contacts which have been designed to close before the circuit breaker main contacts close, or for which times are required (in relation to main contacts) to accurately set the timing of close pulses for synchronising schemes.

When checking operation it is easy also to show that automatic circuits such as reclose will in fact close the circuit breaker (a positive check).

It is just as essential to prove that the circuit does not reclose when not required (a negative check).


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On/Off switches and auxiliaries should be proved to work in the correct part of each circuit.

Finally any earthing and testing plug sets should be fitted to prove that they are usable when required.

15.2 Tests

Tests are to be carried out to cover the requirements described above and to ensure that:

1. The polarity of dc incoming supplies to panels, cubicles, etc, is correct.

2. All relays, which either perform a tripping function, or control a tripping or measuring function in a protective system, operate at 70% nominal volts. This test to be carried out as an overall test and the reduced voltage supply is to be provided by the Commissioning Engineer.

3. All relays other than those specified in (a) above operate at standing battery voltage.

4. All protective and tripping relays, and, where applicable, all control, alarm and indicating relays correctly operate the appropriate indicators and auxiliary relays.

5. All functional links, fuses, auxiliary switches, changeover switches etc provide the designed isolation and are correctly labelled.

6. All alarms and annunciations operate correctly at standing voltage, at local and remote control points, as applicable.

7. All circuit breakers and motorised isolators operate from all control positions and the appropriate control selectors function correctly, that automatic switching and synchronising schemes function correctly and that circuit breakers trip from all the associated trip relays irrespective of selector switch positions.

The following points should be noted with reference to test 2 and 3 above:

a) The operate and reset times for slugged relays and timing relays, and, where applicable, for instantaneous relays in special applications, are to be checked at standing battery volts.

b) ENA TS 48-4 defines class ESI2 (formerly EB2) relays as auxiliary relays which, from the nature of their coil connections, are liable to electrical mal-operation (this category includes 'tripping relays'). Where the nameplates of relays used in such applications are not marked 'ESI2 (EB2)' the relays shall be tested to ensure the requirements of ENA TS 48-4 are satisfied.

c) Except for the relays referred to in a) and b) above, tests, to determine the minimum or maximum, operating or resetting, voltage or current, for particular relays are only to be carried out when such relays are used in special applications, and will not normally be applicable to other auxiliary relays.

Note: An auxiliary relay is an 'all or nothing' relay used to supplement the performance and/or facilities of another relay (e.g. by modifying contact performance or by introducing time delays). An 'all or nothing' relay is a relay having no specified accuracy and which is intended to operate in response to an energising quantity having a value either higher than that at which it picks-up or lower than that at which it drops-off (in the general case the energising quantities will be either normal rated value or zero value respectively).


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16 Full Load Acceptance Test

Full load secondary injection test (to ensure actual protection settings are stable for maximum load current) should be carried out shortly before equipment is energised.

17 Telecontrol Commissioning

For new switchboard installations where the telecontrol wiring is already integrated into the scheme, basic wiring checking as above should have identified any obvious errors or omissions in the telecontrol control, alarm, indication and analogue transducer circuits.

Functional tests of telecontrol equipment are generally carried out in three stages, i.e.

1. Basic functional tests within the switchgear, relay panel and wiring as far as the marshalling cabinet.

2. Tests with the circuits wired through to the telecontrol outstation to prove operation through to Network Control.

3. On-load close-trip-close operations with analogue reading checks and calibration.

4. Once local or standby operation of the switchgear from control switches has been proved, then reselection of the Control Selector switches will allow telecontrol controls to be mimicked from the marshalling cabinet, by applying the rated voltage to the interposing relay coils in turn. Correct operation of two-position control relays (e.g. SEF Off/On, Auto-reclose Off/On) shall be fully proved with the relays in both positions.

Alarms and Indications from the switchgear to the marshalling cabinet can be proved at the open telecontrol links while operating each alarm or indication contact in turn.

Analogue output signals from current and voltage transducers can be checked using an AVO or Fluke on the 10mA dc range, while powering the transducers by secondary injection. Phase angle transducers are difficult to test fully unless either a phase-shifting transformer and a three-phase LV supply or automatic test set are available. It may be necessary to accept on-load readings only as proof of correct connections.


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18 Final On-Load Tests

Before leaving a newly-commissioned scheme in normal service, it is essential to perform a final check that the system load conditions are correctly represented in the CT and VT secondary circuits, relays, transducers etc.

In view of the hazards inherent in these tests they are to be carried out under the direct supervision of the Commissioning Engineer with authority from Network Control. The tests comprise:

Operation and Stability Test – for on load commissioning of unit type protection.

Tests for Restraint – to prove the characteristic of protective schemes with directional qualities.

On-load Checks – to ensure that all connections and test links have been replaced and test leads removed as well as to confirm the integrity of the CT circuits.

On-load trip tests – to ensure local tripping and remote tripping of circuit-breakers via intertrip systems are proven. The trip tests can also incorporate follow on tests to ensure the correct operation of trip relay reset schemes working in conjunction with any automatic isolation and reclosing facilities provided both locally and at the remote end(s) of the circuit.

For currents, on load checks requires split-plug readings to be taken of each phase secondary current, and the values to be checked against ammeter and telecontrol transducer readings according to the CT ratio. Clip-on ammeter probes used in conjunction with a multimeter can also be used for this purpose. There should obviously be no residual (earth-fault) current in the secondary circuits on-load. Where on-load checks are made to transformer differential schemes these will reveal some current flowing in the operate coils if transformer tap selection in not at the nominal position. The tap position should be verified against the measured operate coil spill current for correct relationship. With modern numerical transformer differential relays, checks can be made on the internal relay currents once they have been internally passed through the CT interposing and transformer vector group correction processes within the relay. The magnitude and phase relationship of the internal HV and LV relay currents with the transformer on load at nominal tap position should be that the HV and LV magnitudes should be the same and the phase relationship between the HV and LV sine waves should be in anti-phase with one another (180 degrees apart).

The anti-phase relationship is expected because the CT group on both the HV and LV sides of the transformer will be aligned such that the ‘P1’ side of the CTs are adjacent to their associated windings. Therefore, with load current passing through the transformer you should expect an ‘anti-phase’ secondary current relationship to current entering and leaving the protected zone as would be expected with a circulating current scheme.VT secondary voltages should be checked for correct balanced values between phases and between phases and earth, and correct phase rotation should be proved according to the prevailing local network convention. With new primary plant, phasing out checks will be required using a known VT reference on an un-disturbed circuit VT elsewhere at the sub-station.

Directional relays will require special on-load tests to prove their correct directional sense, as detailed on the relevant test form. A final proof of the correct directionality can sometimes only be achieved using load current. However, the network running arrangement when using this method must be fully considered to ensure that the direction of load is certain. For example, closed bus sections downstream of the relay point may need to be opened first to prevent potential circulating current between parallel transformers from giving mis-leading on-load measurements.


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On load testing is required for unit schemes to prove operation and stability and the relevant test forms and manufacturers recommendations should be followed.

Some equipment will require special testing using energised primary plant, e.g., synchronising circuits. Although such circuits have been thoroughly checked during pre-commissioning some energised checking using system voltage is unavoidable. Precautions should be taken, whenever practicable, to reinforce the circuit under test with a back-up circuit to minimise system disturbance in the unlikely event of mal-operation.

On completion of on-load tests, a final check shall be made to ensure that relay settings are all as required, all fuses and links are correctly in place, and all control and selector switches in the correct position with padlocks fitted. All schematic and wiring diagrams should be brought fully up-to-date and copies left on site.

Where necessary, voltage readings should be taken at the terminals of each relay to ensure that loop connections between relays are complete.

Special attention should be paid to broken-delta voltage and residual current circuits, where zero voltage or current respectively may not be proof of the completeness of the circuit.


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19 Re-commissioning after Fault Repair or Modification

During the service lifetime of a switchboard or relay panel, various component repairs or replacements, or modifications to the scheme, are to be expected.

In such instances, when returning the plant to service, a minimum amount of re-commissioning testing will clearly be required.

As a general guide to the extent of such tests, reference should be made to the original commissioning records, and repeat tests should be carried out for all items of equipment which have been physically changed or modified.

The following specific points should also be observed:

1. Any component on which wiring has been removed or replaced shall be functionally tested to prove its correct action in the scheme.

2. Any 'plug-in' or withdrawable relay module that has been exchanged without disturbing any fixed wiring should at least receive basic functional tests, to prove its correct response to all input currents or control signals.

3. If a protection measuring relay is involved, it should receive the full secondary injection (timing) tests as for normal commissioning.

4. User-programmable electronic relays that have been repaired or replaced are likely to be equipped with a more modern software version than the original.

5. When checking the relay configuration settings against the existing logical schematic diagram, it shall be borne in mind that the old diagram may no longer be exactly applicable to the new software. If in doubt, refer to the latest current issue of logical schematic diagram for that particular scheme and model of relay, and modify or replace the existing site drawing where necessary.

6. With numerical relays ensure that a copy of the ‘as commissioned’ setting and logic files are obtained from the protection database to be installed on the replacement relay. As with the older static relays using logical setting links and/or relay masks, a full functional check will be required to ensure the relay operates correctly within the scheme for which it is applied.

7. On-load tests shall always be repeated when re-commissioning equipment connected to current and voltage transformers.

8. Where revised test results have been obtained, the new test sheets should be securely attached to the original commissioning test records, and the obsolete existing results crossed through.

9. Schematic and wiring diagrams shall always be checked for errors and marked- up as necessary to show the new as-installed arrangement.


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20 References

20.1 UK Power Networks Standards

ECP 11-0001 Grid and Primary Installation and Commissioning Requirements

ECP 11-0002 Secondary Substation Commissioning Requirements

ECP 11-0006 High Voltage Testing Requirements

HSS 40 052 Energisation and Disconnection of Electrical Apparatus and Plant including all Cables

UK Power Networks Distribution Safety Rules

20.2 National Standards

Health and Safety at Work Act 1974

Management of Health & Safety at Work Regulations 1992

Electricity at Work Regulations 1989

Electricity Safety, Quality and Continuity Regulations 2002

ENA TS 41-36 Distribution switchgear for service up to 36kV (cable and overhead conductor connected)

ENA TS 48-4 DC relays associated with a tripping function in protection systems

IEC 60255 Part 3 Electrical Relays


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Appendix A – Diagrams

O/C

O/C

O/C

E/F

C11

C31

C51

C50

C30

C10

C70

C12

C32

C52

(R)

(Y)

(B)

C71

R

Y

B

MAIN

CIRCUIT

BREAKER

OPEN

RELAY TEST

BLOCK OR

PLUG

BRIDGE

A

V

TEST-SET VARIABLE

VOLTAGE OUTPUT OR

VARIAC TRANSFORMER

230V 8A

C90

W2 X11

K3K1

230V AC

SUPPLY

SPLIT-PLUG

P1

P2

S1

S2

S1

S2

S1

S2

ISOLATING

TRANSFORMER IF

REQUIRED

Methodology:

It is usual, before taking detailed test measurements, to raise the applied voltage slowlyuntil a proportionately large (but not excessive) 'saturation' current begins to flow,

thereby indicating the approximate knee-point voltage and hence the appropriate

voltage intervals to be applied when plotting results. Injected current should always bereduced slowly from the maximum 'saturated' value to zero (e.g. by adjusting the

Variac output) in order to demagnetise the CT core before commencing the test, which

should start from zero with progressively rising values of applied Voltage.

Figure A-1 – Test Circuit for CT Magnetisation Curves


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Test Results

Applied Volts (V) 2.5 5 10 15 20 25 30 32.5 34 35

Current Drawn (mA) 24 35 49 62 76 96 130 160 195 240

Curve Plotted from Results

0

5

10

15

20

25

30

35

40

24 35 49 62 76 96 130 160 195 240

mA

Vo

lts

50% more current

10% more

voltsKNEE

POINT

Figure A-2 – CT Magnetisation Curve Example


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P2

S2 S1

+-

+-

BATTERY

P1

mA

PUSH

BUTTON

+-

+

IF POLARITY IS CORRECT METER WILL GIVE:

+VE DEFLECTION OM PUSH BUTTON MAKE

-VE DEFLECTION ON PUSH BUTTON BREAK

-

Figure A-3 – Flick Test for CT Polarity


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A

O/C

O/C

O/C

E/F

C11

C31

C51

C50

C30

C10

C70

C12

C32

C52

(R)

(Y)

(B)

C71

R

Y

B

MAIN CIRCUIT

BREAKER (SERVICE

POSITION) OPEN

RELAY TEST

BLOCK OR

PLUG

BRIDGE

PRIMARY

INJECTION TEST

SET

A

TEMPORARY

SHORTING LOOPS

(OR USE CIRCUIT

BREAKER IN CABLE

EARTH POSITION)

C90

W2 X11

K3K1

RELAY

SPLIT-PLUG

P1

P2

S1

S2

S1

S2

S1

S2

Figure A-4 – CT ratio and Polarity Check by Primary Injection


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HV LV

Biased-differential relay

HV REFrelay

LV REFrelay

Figure A-5 – Typical Bias Differential and Earth Fault Protection Scheme for Yd1 Transformer (+90 Connection)


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Assumed three phase fault

location

HV LV


HV REFrelay

LV REFrelay

Figure A-6 – Typical Scheme for Yd1 Transformer – Proof for Phase through Fault Stability


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Assumedearth fault

location

HV LV


HV REFrelay

LV REFrelay

Figure A-7 – Typical Scheme for Yd1 Transformer – Proof for Earth through Fault Stability


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A

HV LV


HV REFrelay

LV REF relay

PRIMARY

INJECTION TEST

SET

A

Notes

Note 1: Temporary Short circuit of stabilising resistors

Note 2: Check current through rely by plugging relay or relay test blocks–

ensure relay short time rating not exceeded

A

Note 2

Note 2

Figure A-8 – Typical Scheme for Yd1 Transformer – Simulated Internal Earth Fault (Operate) Conditions


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HV LV

HV REFrelay

LV REF relay

PRIMARY

INJECTION TEST

SET

A

A

Note 2

Note 2

A


Figure A-9 – Typical Scheme for Yd1 Transformer – Simulated Internal Earth Fault (Stability) Conditions


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O/C

O/C

O/C

E/F

C11

C31

C51

C50

C30

C10

C70

C12

C32

C52

(R)

(Y)

(B)

C71

R

Y

B

MAIN

CIRCUIT

BREAKER

OPEN

RELAY TEST

BLOCK OR

PLUG

BRIDGE

C90

W2 X11

K3K1

A TIMER

START/STOP

50A 25A 5A 1ACOM

CURRENT

FILTER

UNIT

(WHEN

REQUIRED

)

SEPARATE

AMMETER (FOR

ACCURACY)

SECONDARY INJECTION

TEST SET

RELAY

A

SPLIT-PLUG

P1

P2

S1

S2

S1

S2

S1

S2

N.B. ENSURE TRIP

CONTACTS ARE

MADE DEAD BEFORE

CONNECTING TIMER

CURRENT

INJECTED TO

WIRE

NUMBERS

RELAY

ELEMENTS

OPERATED

C12 & C70 R & E/F

C32 & C70 Y & E/F

C52 & C70 B & E/F

C12 & C71 R ONLY

C32 & C71 Y ONLY

C52 & C71 B ONLY

C71 & c70 E/F ONLY

C12 & C32 R & Y

C32 & C52 Y & B

C52 & C12 B & R

Figure A-10 – CT Relay Secondary Injection Tests


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Appendix B – Overcurrent Relay Characteristics

t13.5

I 1 t 4.5

Extremely Inverse Curve ( 1< I >1.3 to start timing f unction)

I 2 t80

I2

1

t 26.667

I 4 t80

I2

1

t 5.333

Long time earth fault Curve ( 0.75< I >1.1 to start timing f unction)

I 2 t120

I 1 t 120

I 4 t120

I 1 t 40

I 11 t120

I 1 t 12

Normal Inverse Curve ( 1< I >1.3 to start timing f unction)

t = seconds to operate I = multiple of setting current

I 2 t0.14

I0.02

1

t 10.029 or nominally 10 sec

I 4 t0.14

I0.02

1


I 10 t0.14

I0.02

1


These times are all with a time mulitplier (TM) of 1.0

A conv enient check of the TM can be made a 4 times setting with TM = 0.2.

The time wil then be (5 x 0.2) = 1 sec nominal.

If required f or maximum accuracy a timing test can be made at the required

in-serv ice relay setting, when it is known.

Other charachterisitcs y ield the f ollowing times at TM = 1.0 which can be

used as test points .

Very Inverse Curve ( 1< I >1.3 to start timing f unction)

I 2 t13.5

I 1 t 13.5

I 4

ecp 11-0003 testing and commissioning guidance...

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