module 2 commissioning switchgear assemblies

SUBSTATION COMMISSIONING COURSE of 48

SUBSTATION COMMISSIONINGCOURSE

MODULE TWO

COMMISSIONING SWITCHGEAR ASSEMBLIES

Written by:Raymond Lee, Technical trainerCopyright ©2010

Electrical Industry Training Centre of Alberta4234 – 93 StreetEdmonton, Alberta, Canada

Phone: (780) 462-5729Fax: (780) 437-0248

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TABLE OF CONTENTS

Headings Page

INDEX OF TABLES.....................................................................................3Introduction:..................................................................................................41. Electrical Testing.......................................................................................5

1.1 Insulation Resistance Test......................................................................5

1.2 Insulation Resistance Test Procedure:....................................................7

1.3 AC Hipot Test......................................................................................11

1.4 AC Hipot Test Procedure.....................................................................14

1.5 DC Hipot Test......................................................................................15

1.6 DC Hipot Test Procedure:....................................................................16

1.7 Low Resistance Test.............................................................................17

1.8 Low Resistance Test Procedure...........................................................18

2. Safety Awareness and Practices.............................................................202.1 Qualifications of A Qualified Person...................................................20

2.2 Recommended Practices......................................................................22

2.3 Excerpts from IEEE Standard 510-1983..............................................23

2.31 Scope...............................................................................................23

2.3.2 Test Area and Safety Prctice..........................................................24

2.3.3 Control and Measurement Crcuits..................................................24

2.3.4 Safety Rules....................................................................................25

2.3.5 Safety Inspection............................................................................25

2.3.6 Grounding and Shorting.................................................................25

2.3.7 Spacing...........................................................................................26

2.3.8 High Power Testing........................................................................26

2.3.8 General...........................................................................................27

3. NETA Acceptance Testing Procedures.................................................283.2 Electrical Tests.....................................................................................30

TABLE OF CONTENTS

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Headings Page

3.3 Test Values Analysis............................................................................33

3.3.1 Visual and Mechanical...................................................................33

3.3.2 Electrical.........................................................................................33

4. Test Set Operational Instruction Manual.............................................415. Switchgear Commissioning Test Forms................................................426. References and Suggested Readings......................................................46

INDEX OF TABLES

Headings Page

Table 1: Preferred voltage and insulation levels for Metalclad switchgear. .11

Table 2: Bolt Torque Specifications for Electrical Connections..................34

Table 3: Insulation Resistance Test Values..................................................36

Table 4: Insulation Resistance Conversion Factor (20ºC)............................37

Table 5: Switchgear Withstand Test Voltages..............................................38

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Introduction:This module will introduce the NETA acceptance testing procedures for the switchgear assembly; the mechanical and visual inspections, the bus bar resistance test, insulation resistance test and the dielectric withstand stand test. The procedure comprises of visual and mechanical inspections, electrical tests and an assessments of the test results. The discussion presented in this module is limited to the testing requirements for switchgear assemblies. Factors which may influence testing of transformers, reactive equipment or highly capacitive insulation systems and cables are covered in other modules, these factors are seldom encountered when testing switchgear assemblies

A brief discussion on the purpose and methods for conducting the aforementioned tests are included. Theoretical information are supported with demonstrations of the test equipment operations and hands-on testing procedures in a simulated substation environment to provide the participants with the basic skills needed to test the insulation system for metal enclosed and metalclad switchgears.

The Electrical Safety section discusses the hazard of the job with high voltage testing and shock hazards. Understanding the hazards, being properly trained in the operation of the test equipment, understanding and being able to perform the procedures are requirements for performing the job safely and properly. Adopting a safe working practice is paramount to everyone’s safety.

By the end of this module the participants will have the basic skills to perform acceptance testing for switchgear assemblies, understand and operate insulation and dielectric test equipment, complete visual and mechanical inspection, and complete inspection / test forms and make proper assessment of the test results.

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1. Electrical TestingThe majority of testing performed in the electrical power system is related to the verification of the insulation system, its quality or integrity. Optimally, electrical testing should be performed in an environment as clean, dry and warm as possible, where all surface contaminations are wiped clean without evidence of left-over residue, these conditions are similar to a factory test environment.

Solid Insulation testing comprise of: Insulation Resistance test Dielectric Withstand (AC or DC) test

The insulation resistance test is the first test that should be performed for testing the primary insulation system of a new switchgear. This is a DC voltage test conducted at a level that does not exceed the rated operating voltage. The result of the test serves as a preliminary assessment of the primary insulation system to determine if it is should be subjected to the High-potential (Hipot) test.

The DC-or AC Hipot test is commonly referred to as the “dielectric over-potential withstand test”. The test applies a voltage level higher than the normal working level to stress the insulation system. The purpose of the test is to confirm that the insulation system can withstand high voltage spikes, transients and surges that can appear in the power system due to switching, lightning induced overvoltages, and other transient conditions that stress the insulation above the normal operating level.

1.1 Insulation Resistance TestThe insulation resistance test is a DC voltage test conducted at 100% of the rated AC insulation phase-to-ground crest level. The DC equivalent is at 1.414 of the AC RMS rated insulation value. The test is conducted with the draw-out circuit breaker in the connected position.

Note: The above value is higher than the recommended NETA insulation resistance test level. In the opinion of this writer, the higher value is a more practical level since the insulation will be stressed at the operating value.

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Example calculation:

Determine the DC Insulation Resistance test voltage for a 5 kV switchgear.

Rated insulation level = 5 kVPhase to-ground voltage = (5 kV) / (1.732) = 2.887 kVAC crest voltage = (2.887 kV) x (1.414) = 4.082 kVDC Test voltage = 4.1 kV

The test voltage is to be increased gradually from zero at a rate no greater than 1000 volt per second to reach the required test voltage within 60 seconds and shall be held there for 1 minute. Insulation value is recorded at the end of the 1 minute period.

The minimum require insulation resistance is listed in Table 3.

Note: A per-phase insulation resistance can be made with the other phases ground if necessitated by the customer.

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1.2 Insulation Resistance Test Procedure:1. Isolate the equipment from any possibility of inadvertent application of

power. Apply isolation and lock-out procedures. Apply working safety grounds as required or if incoming lines are subjected to induced voltage from adjacent or nearby high voltage sources. Obtained test and work permit as required.

2. Isolate the working area by installing DANGER HIGH VOLTAGE – TESTING IN PROGRESS – DO NOT ENTER signs using barrier tape / rope at a visible working height to prevent unwanted visitors into the area. Only designated and qualified personnel assigned to perform the test should be in the working area.

3. Isolate the equipment by disconnecting the all incoming and outgoingcables. Disconnected cables should have clearance from the switchgear terminals greater that the phase spacing distance. Use nylon twine to hold cable lugs away from incoming and outgoing terminals as required.

4. Disconnect any surge arrestors and primary fuses from VT’s and CPT’s

5. For equipment with stationary mounted devices and for equipment with drawout devices, position the devices in the connected position:

a) Ensure that the equipment is properly grounded.

b) Close the main contacts of the switching or interrupting devices.

c) Apply the test voltage at the test duration on the primary terminal to each phase of the switchgear assembly individually with the frame and all other phases grounded.

d) Discharge / ground the tested phase before removing the test set’s high voltage lead.

e) Review the test data

The DC insulation resistance test is the first test to be conducted to determine the insulation system integrity and if it can be subjected to the dielectric withstand tests.

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If the insulation test results are satisfactory, the dielectric test can be performed.

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Examples of safety warning signs:

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Examples of barrier tape and high visibility barrier rope:

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1.3 AC Hipot TestThe AC hipot testing of switchgear assemblies is conducted at the rated power frequency, at 75% of the factory test voltage level for the same test. The test is conducted with the draw-out circuit breaker in the connected position.

The AC test voltage shall have a crest equal to 1.414 times the RMS value specified in Table 5. The wave shape shall be essentially sinusoidal. The frequency shall be within 20% of the rated power frequency. The test voltage is to be increased gradually from zero at a rate no greater than 1000 V per second to reach the required test value and shall be held there for 1 minute.

IEEE C37.20.2 section 6.5 for Field dielectric test states:When power frequency withstand test are to be made on Metalclad switchgear after installation in the field, the switchgear shall not be tested at greater than 75% of the test values given in Table 1 …for the procedure.

Table 1: Preferred voltage and insulation levels for Metalclad switchgear

Rated maximum voltage

(kV rms)

Insulation levelsPower frequency

withstand(kV rms)

Lighting impulse withstand(kV rms)

Referencea

dc withstand(kV rms)

4.76 19 60 278.25 36 95 5015.0 36 95 5027.0 60 125 b

38.0 80 150 b

aThe column headed dc withstand is given as a reference only for those using dc test to verify the integrity of connected cable installations without disconnecting the cables from the switchgear. It represents values believed to be appropriate and approximately equivalent to the corresponding power frequency withstand test values specified for each voltage rating of switchgear. He presence of this column in no way implies any requirements for a dc withstand test on equipment or implies that a dc withstand test represents an acceptable alternative to the power frequency withstand test specified in this standard for design tests, production test, conformance tests, or field test. In making dc tests, the voltage should be raised to the test value in discrete steps and held for a period of 1 min.bBecause of the variable voltage distribution encountered when making dc withstand test, the manufacturer should be contacted for recommendations before dc withstand test are applied to the switchgear.

All rating is based on a rated power frequency of 60 Hz. [1]

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Figure 3: AC High Potential Dielectric Withstand Test Connections

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1.4 AC Hipot Test Procedure1. Isolate the equipment from any possibility of inadvertent application of power.

Apply isolation and lock-out procedures. Apply working safety grounds as required or if incoming lines are subjected to induced voltage from adjacent or nearby high voltage sources. Obtained test and work permit as required.






b) Close the main contacts of the switching or interrupting devices.

f) Apply the test voltage at the test duration on the primary terminal to each phase of the switchgear assembly individually with the frame and all other phases grounded.

c) Discharge / ground the tested phase before removing the test set’s high voltage lead.

d) Open the main contacts of the switching or interrupting devices.

Caution: Application of high voltage potential across an open vacuum gap can produce x-ray radiation. Door should be closed and testing station should be located to minimize exposure.

e) Ground all outgoing terminals

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f) Apply the test voltage for the test duration on the primary terminal to each phase of the switchgear assembly individually, with the frame and all other phases grounded.

g) Discharge / ground the tested phase before removing the test set’s high voltage lead.

h) Review the test data

i) Reconnected all disconnected surge suppressors.

The AC Hipot test is a go-no-go test and considered by many as a destructive test. There is very little warning or indication to the tester if an insulation will fail. The failure event is a rapid process and does not give the tester the change to abort the test at the incipient point of failure.

Note: If the application of the AC dielectric withstand is satisfactory, both the switchgear insulation system and the breaker (vacuum bottle integrity) dielectric test have been completed. Breaker testing is presented in other module.

Note: Some manufacturer recommend the application of Low Frequency Withstand voltage test versus the Power Frequency Withstand voltage test for their breaker insulation system and vacuum bottle integrity test. While the voltage levels are the same at 75% of C37.20.2, the removal of the breakers from the connected position should be considered.

1.5 DC Hipot TestThe DC Hipot testing of switchgear assemblies is not a recommended test. DC dielectric withstand test values are included in IEEE C37.20.2 for situation where testing of cable insulation system would better be performed without the disconnecting the cables. Application of this test is used determines integrity of the cable insulation system combined with that of the switchgear assembly.

Caution: The application of high DC potential across a vacuum breaker contacts can produce exposure to X-ray radiation. For this reason the drawout breakers must be moved to the disconnected position or removed from the cubicles.

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Note: The manufacturer should be consulted before attempting to perform the DC dielectric withstand test which involves the switchgear assemblies.

The DC Hipot test produces corona and tracking at high voltage levels due to the concentration of dielectric field lines at sharp edges and end points, its use is limited to testing up to 15 kV class equipment.

When dc voltage is used, the following additional precautions should be taken:a) Wound type current transformer with primary windings in the primary

circuits must be disconnected or have the primary winding shorted.b) The dc hipot voltage used must not exceed 75% of the values given in

Table 1.

The test voltage is to be increased in discrete steps to reach the required test value within 60 to 90 seconds and shall be held there for 1 minute. Leakage current should be stable before the next voltage increase is applied.

Caution: The use of full wave bridge circuitry produces smaller peak voltages that half-wave bridge and is the recommended equipment for the DC Hipot tester. The maximum ripple factor should not exceed 3%.

Figure 4: DC High Potential Dielectric Withstand Test Connection

1.6 DC Hipot Test Procedure:1. Isolate the equipment from any possibility of inadvertent application of power.


2. Isolate the working area by installing DANGER HIGH VOLTAGE – TESTING IN PROGRESS – DO NOT ENTER signs using barrier tape / rope at

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a visible working height to prevent unwanted visitors into the area. Only designated and qualified personnel assigned to perform the test should be in the working area.



5. For equipment with stationary mounted devices and for equipment with drawout devices, position all vacuum drawout devices in the disconnected position.


b) Apply the test voltage at the test duration on the primary terminal to each phase of the switchgear assembly individually with the frame and all other phases grounded.

c) Review the test data

1.7 Low Resistance TestThe low resistance test measures the bolted connection resistances in the primary circuit. The test is performed with by injecting a currents at 100 ADC or higher. Currents above 50A are recommended per IEC to reduce the errors in measurement readings due to galvanic effects encountered when testing with a low current test sets.

Low resistance measurements are conducted after bolted connections are inspected and torque to the recommended levels as listed in Table 2.

Resistance value should be compared to values of similar bus connections. Connections which exhibit values that greater than 50% of the lowest value should be investigated and corrected. Dismantling of the connections may be required to affect repair; all repaired connections must be retested.

Access to the main bus bolted connections requires removal of compartment’s metal barriers and the insulating boots which covers the bolted connections.

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Resistance measurements are performed on a per phase circuit with one of the current source leads connected at one end and the second current source lead connected to the other end to include as may bolted joints as possible within the current circuit. The voltage drop across the joints are read by a pair of voltage measuring leads connected to either sides of the connections; the measured voltage drop will be converted into resistance value by the measuring instrument.

Note: For the resistance reading to be accurate, a series current circuit path must be maintained.

Figure 1: Simplified bus-bar construction showing locations of current injection and voltage measuring points.

[2]

Typical values for bolted joint should be less than 20μΩ.

Resistance values are calculated based on Ohm’s law:

R = V / I

Example calculation: 1 mV drop across a bolted joint equates to 10 μΩ (1 X 10-3 V) / (1 x 102 A) = 1 x 10-5 = 10 x 10-6

1.8 Low Resistance Test Procedure1. Isolate the equipment from any possibility of inadvertent application of power.


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g) Close the main contacts of the switching or interrupting devices.

h) Apply the test current +ve lead at the incoming primary terminal on phase-A and the –ve lead at the extreme end on phase-A bus bar.

i) Measure and record the first bolted resistance with the voltage measuring leads starting from the +ve current lead and working towards the –ve current lead. Note position of bolted joint via cubicle location.

j) Repeat low resistance measurements for phase-B and phase-C busbars bolted joints by applying current to the respective phase during testing.

k) Measure all cable to bus-bar bolted joint resistance

l) Apply the test current +ve lead at the incoming primary terminal on phase-A and the –ve lead at the outgoing phase-A for the first breaker.

m) Measure and record the incoming and outgoing sliding contacts resistance and the main contact resistance.

n) Repeat low resistance measurements for phase-B and phase-C incoming and outgoing sliding contacts resistance and the main contact resistance by applying current to the respective phase during testing.

o) Repeat steps l) through n) until all breaker resistance measurements are completed.

p) Review the test data.

Note: Connections which exhibit values that greater than 50% of the lowest value should be investigated and corrected

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2. Safety Awareness and PracticesConducting a high voltage test represent an electrical shock hazard to the person who is conducting the test and anyone else that may come in contact with energized equipment.

Test set operators must: be aware of the hazards involved in performing the task take the required safety precautions and restrict access to anyone not

involved in the testing process be properly trained in the equipment operations recognize and avoid the hazards be trained in safe work practices and procedures.

Qualified PersonA qualified person shall be trained and be knowledgeable of the construction and operation of equipment or a specific work method, and be trained to recognize and avoid the electrical hazard that might be present with respect to that equipment or work method. Such persons shall also be familiar with the proper use of special precautionary techniques, personal protective equipment, insulating and shielding material, and insulating tools and personal protective equipment.

It is the employer’s responsibility to provide safety-related work practices, maintain a safe working environment and train the employees implementing those practices.

2.1 Qualifications of A Qualified PersonTen useful knowledge that a qualified person should have as it pertains to high voltage testing:

1. A qualified person should have the basic understanding of electricity, voltage, current, resistance and how they relate to each other. A qualified person should understand conductors, insulators and grounding systems.

2. A qualified person should have a working knowledge of the test equipment, the test that are being performed, the circuits that are being energized and the hazard associated with the tests.

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3. A qualified person should understand the approach distance and corresponding voltages to which they may be exposed.

Test Voltage levelsAC/DC voltage

Restricted approach boundary

Prohibited approachboundary

Up to 750v 1.0 ft 1 in751v to 15 kV 2 ft 2 in 7 in15.1 – 36 kV 2 ft 7 in 10 in36.1 – 46 kV 2 ft 9 in 1 ft 5 in

46.1 – 72.5 kV 3 ft 3 in 2 ft 2 in72.6 – 121 kV 3 ft 4 in 3 ft 4 in

4. A qualified person should be trained in safety-related work practices and procedural requirements as necessary to provide protection from the electrical hazards associated with their respective job or task assignments.

5. A qualified person should understand that the primary factors that determine the severity of electric shock are:

A. The amount of current flowing through the bodyB. The path of the electric current through the bodyC. The duration or length of time the person is exposed

6. A qualified person should know that the human body respond to current in the following manner:

BODILY EFFECT DC mA 60 Hz AC mASlight sensation felt at hand(s)

Men = 1.0 Men = 0.4Women = 0.6 Women = 0.3

Threshold of perception Men = 5.2 Men = 1.1Women = 3.5 Women = 0.7

Painful, voluntary muscle control ok

Men = 62 Men = 9Women = 41 Women = 6

Painful, unable to let-go


Severe pain, difficulty breathing


Possible heart fibrillation in 3 seconds


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7. A qualified person working on or near exposed energized electrical conductors or circuit parts should be trained in methods of release of victims from contact with exposed energized or circuit parts.

8. A qualified person should understand that the test instrument is a variable voltage power source and the current will flow to any available ground path. They should be aware that contacting the device under test (DUT) during the test can result in a dangerous shock hazard under certain conditions.

9. A qualified person should understand that if the enclosure is not grounded the enclosure can become energized through capacitive coupling.

10.A qualified person should be made aware of the importance of discharging a DUT. The use of a discharge stick connected to ground must be applied before attempting to lift the high voltage lead from the device DUT. For certain test the DUT must be discharge for longer than it has been energized to remove all stored charge.

11. A qualified person should also be trained in the care, use and inspection of any PPE and insulating tools required to do the job

12. Qualified persons should perform a functional verification test on the test equipment and confirm all safety interlocks and emergency shutdown devices are operating before commencing any tests.

Engineering controls and work practices should be the primary factor in safeguarding against the risk of injury. Safety controls should be in place to provide for the highest level of protection.

2.2 Recommended PracticesIt is beyond the scope of this module to cover safety practices when working with high voltage, testing with high voltage or elaborating on the current rules and safety practice regulations. Our suggestion is to source the relevant information for the following publication as well as sourcing the site specific safety requirement at the job site.

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2.3 A Brief Explanation of IEEE Standard 510-1983

2.31 ScopeConsiderations of safety in electrical testing apply to both personnel and equipment and apparatus or system under test. These recommended practices deal with safety in connection with testing in the field, and using high voltage power supplies. For the purposes of these recommended practices, a voltage of 1,000 volts and above are considered.

1. All ungrounded terminals of the test equipment or apparatus under test should be considered as energized.

2. Common ground connections should be solidly connected to both the test set and the DUT. The current capacity of the ground leads should sized to carry the maximum possible ground current. The effect of ground potential rise due to high impedance ground connection should be considered.

3. Precautions should be taken to prevent accidental contact of live terminals by personnel by the use of shielding or barriers around live terminals.

4. Equipment should include metering for indicating the test voltages.

5. Emergency shut-off, automatic shutdown or a safety watch with shut-off controls via dead man’s switch should be present for the immediate de- energization of test circuits. For dc testing, provisions for discharging and grounding of charged terinals should also be included.

6. High Voltage tests should be performed and supervised by qualified personnel.

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2.3.2 Test Area and Safety Practice

1. Appropriate warning signs, DANGER – HIGH VOLTAGE, and barrier should be installed.

2. Safety grounds should be provided applied to all in-feed circuits. The use of insulated handle grounding stick is recommended for discharging tested terminals and discharging terminals before manual connections are made. In the case of several capacitors connected in series, the exposed intermediate terminals should also be grounded. This applies to impulse generators where the capacitors should be short-circuited and grounded before and while working on the generator.

3. Equipment safe ground should take precedence over signal ground connections unless special measures are taken to ensure personnel safety.

2.3.3 Control and Measurement Circuits

1. Keep leads a short as possible and protect their structural and insulating capabilities. Control wiring, meter connections, and cables running to oscilloscopes fall into this category. Meters and other instruments with accessible terminals should not be exposed.

2. Temporary Circuits

a. Temporary measuring circuits should be located completely within the test area and viewed remotely. Alternatively, the meters may be located outside the fence, provided the meters and leads, external to the area, are enclosed in grounded metallic enclosures.

b. Temporary control circuits should be treated the same as measuring circuits and housed in a grounded box with all controls accessible to the operator at ground potential.

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2.3.4 Safety Rules

A set of safety rules should be established and enforced for the field applications. Safety rules should be disseminated to anyone doing testing. Safety rules should be reviewed periodically by everyone involved in testing. A safety audit should be performed yearly.

2.3.5 Safety InspectionInspection of the test areas should be carried out on an on-going basis. The recommendations from these inspections should be followed. Corrective actions for unsafe equipment made.

NOTE: A safety committee composed of several operators appointed on a rotating basis is an suggested and helps making all personnel aware of safety.

2.3.6 Grounding and Shorting1. The routing and connections of temporary wiring should be secure against

accidental interruptions or tripping that may create hazard to personnel or equipments.

2. Devices which use solid or solid/liquid dielectric for insulation should be grounded and short-circuited when not in use.

3. Short circuit capacitive objects in the following manner:

a. Any capacitive object not in use that may be influence by a dc electric field should have its exposed high-voltage terminal grounded. This will prevent inadvertent shock from a voltage built up in the capacitive object.

b. Capacitive objects having a solid dielectric should be short-circuited after dc proof testing. This precaution will prevent a voltage build up due to dielectric absorption until the object has been reconnected to a circuit.

NOTE: It is good practice for all capacitive devices to remain short-circuited when not in use.

c. Any open circuited capacitive device should be short-circuited and grounded before being contacted by personnel.

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2.3.7 Spacing1. All objects at ground potential must be placed away from all exposed high

voltage points at a minimum distance of 1 inch for every 7,500 Volts.

Example: 50 kV requires a spacing of at least 6.7 inches

50 kV / (7.5 kV / in) = 6.7 in

2. Allow a creepage distance of 1 inch for every 7,500 Volts for insulators placed in contact with high voltage points.

2.3.8 High Power Testing1. High-power testing involves a special type of high-voltage measurement in

that the level of current is very high. Careful consideration should be given to safety precautions for high-power testing due to this fact. The explosive nature of the test specimen also brings about special concern relating to safety in a small environment.

2. Protective eye and face equipment should be worn by all personnel conducting or observing a high-power test where there is a chance that eye or face injury can be prevented.

NOTE: Typical eye and face hazards present in high-power test areas included intense light (including ultraviolet), sparks, and molten metal.

3. Safety glasses containing absorptive lenses should be worn by all personnel observing a high-power test even when electric arcing is not expected. Lenses should be impact-resistant and have shade numbers consistent with the ambient illumination level of the work area but yet capable of providing protection against hazardous radiation due to any inadvertent electric arcing.

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2.3.8 General

1. All high-voltage generating equipment should have a single obvious control to switch the equipment off under emergency conditions.

2. All high-voltage generating equipment should have an indicator which signals that the high-voltage output is enabled.

3. All high-voltage generating equipment should have provisions for external connections (interlock) which, when open, cause the high-voltage source to be switched off. These connections may be used for external safety interlocks in barriers or for a foot or hand operated safety switch.

4. The design of any piece of high-voltage test equipment should include a failure analysis to determine if the failure of any part of the circuit or the specimen to which it is connected will create a hazardous situation for the operator. The major failure shall be construed to include the probability of failure of items that would be overstressed as the result of the major failure. The analysis may be limited to the effect of one major failure at a time, provided that the major failure is obvious to the operator.

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3. NETA Acceptance Testing ProceduresEn situ commissioning tests should be performed on newly installed equipment to ensure that the equipment will meet the requirements as detailed in the design specifications. The NETA standards should be used in the absence of manufacture’s instructions for acceptance testing procedures.

Note: Always consult the manufacturer’s manual for information on the required tests to be performed and the test levels to be applied.

3.1 Visual and Mechanical Inspection1. Compare equipment nameplate data with drawings and specifications.

The following minimum information shall be given on the nameplate: Point of assembly Type and designation Identification reference Rated maximum voltage (where applicable) Rated power frequency (where applicable) Rated insulation level (power frequency withstand and lightning impulse

withstand) Rated continuous current Rated short-time withstand current Rated momentary withstand current Date of manufacture

2. Inspect physical and mechanical condition.

3. Inspect anchorage, alignment, grounding, and required area clearances. Review manufacture’s manual for anchorage requirement.

4. Verify the unit is clean and all shipping bracing, loose parts, and documentation shipped inside cubicles have been removed.

5. Verify that fuse and circuit breaker sizes and types correspond to drawings and coordination study as well as to the circuit breaker’s address for microprocessor-communication packages.

6. Verify that current and voltage transformer ratios correspond to drawings.

7. Verify tightness of accessible bolted electrical connections by calibrated torque-

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wrench method in accordance with manufacturer’s published data or Table 2.

8. Confirm correct operation and sequencing of electrical and mechanical interlock systems.

i. Attempt closure on locked-open devices. Attempt to open locked-closed devices.

ii. Make key exchange with devices operated in off-normal positions.

9. Verify appropriate lubrication on moving current-carrying parts and on moving and sliding surfaces. Refer to manufacturer’s instruction manual.

10.Inspect insulators for evidence of physical damage or contaminated surfaces.

11.Verify correct barrier and shutter installation and operation.

12.Exercise all active components.

13.Inspect mechanical indicating devices for correct operation.

14.Verify that filters are in place and vents are clear.

15.Perform visual and mechanical inspection of instrument transformers as outline in the Instrument Transformer Commissioning procedure.

16.Inspect voltage and control power transformers.

i. Inspect for physical damage, cracked insulation, broken leads, tightness of connections, defective wiring, and overall general condition.

ii. Verify that primary and secondary fuse or circuit breaker ratings match drawings. Primary circuits of all voltage transformers shall include current limiting

fuse Secondary circuits of all voltage transformers shall include fuses or their

equivalent

iii. Verify correct functioning of drawout disconnecting and grounding contacts and interlocks.

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The primary fuses of transformers shall be mounted in such a way that they must be disconnected from the primary circuit before access can be obtained. Provisions shall be made for disconnecting or automatically grounding the secondary circuit of the voltage transformers when the primary circuit is disconnected.

3.2 Electrical Tests1. Perform resistance measurements through bolted electrical connections with a

digital low-resistance ohmmeter if applicable.

2. Perform insulation-resistance tests on the complete primary bus assembly phase-to-ground, with the breakers closed in the connected position and VT doors closed with the primary fuses removed. Apply the DC test voltage for 1 minute at the rated AC crest value.

Dielectric withstand voltage tests shall not proceed until insulation-resistance levels are raised above minimum values as listed in Table 3.

3. Perform an AC dielectric withstand voltage test on each bus section, each phase-to-ground with phases not under test grounded, in accordance with manufacturer’s published data. If manufacturer has no recommendation for this test, it shall be in accordance with Table 5. The test voltage shall be applied for one minute.

4. Perform insulation-resistance tests on control wiring with respect to ground.

Applied potential shall be:500 volts dc for 300-volt rated cable,1000 volts dc for 600-volt rated cable.

Test duration shall be one minute. For units with solid-state components or control devices that can not tolerate the applied voltage, follow the manufacturer’s recommendation.

5. Perform electrical tests on instrument transformers.Refer to Module 3 on commissioning Instrument Transformer.

6. Perform ground-resistance tests.Refer to module (future).

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7. Determine accuracy of all meters and calibrate watthour meters. Verify multipliers.

Refer to module (future).

8. Control Power Transformers

i. Perform insulation-resistance tests. Perform measurements from winding-to-winding and each winding-to-ground. Test voltages shall be in accordance with Table 4 unless otherwise specified by the manufacturer.

ii. Perform a turns-ratio test on all tap positions.

iii. Perform secondary wiring integrity test. Disconnect transformer at secondary terminals and connect secondary wiring to a rated secondary voltage source. Verify correct potential at all devices

iv. Verify correct function of control transfer relays located in the switchgear with multiple control power sources.

9. Voltage Transformers

i. Perform insulation-resistance tests. Perform measurements from winding-to-winding and each winding-to-ground. Test voltages shall be in accordance with Table 4 unless otherwise specified by the manufacturer.

ii. Perform a turns-ratio test on all windings.

i. Perform secondary wiring integrity test. Disconnect transformer at secondary terminals and connect secondary wiring to a rated secondary voltage source. Verify correct potential at all devices.

Note: Item 9 is duplicated here and is also included in the Instrument Transformer commissioning module.

10. Perform current-injection tests on the entire current circuit in each section of switchgear.

i. Perform current tests by secondary injection with magnitudes such that a minimum current of 1.0 ampere flows in the secondary circuit. Verify correct magnitude of current at each device in the circuit.

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11. Perform system function tests.

12. Verify operation of cubicle switchgear/switchboard space heaters.

13. Perform phasing checks on double-ended or dual-source switchgear to insure correct bus phasing from each source.

14 Perform load tests;

i. Verify correct secondary voltages on all potential terminals fed from the Control Power Transformer. Verify the magnitude in reference to ground potential.

ii. Verify correct secondary voltages potential on all potential terminals fed from the Voltage Transformer. Verify phase rotation and magnitude in comparison to Phase-A to ground reference voltage for all tests.

iii. Verify correct secondary current phase rotation for all relays and meters at the metering jacks and all relays with applicable metering provisions.

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3.3 Test Values Analysis

3.3.1 Visual and Mechanical1. Bolt-torque levels shall be in accordance with manufacturer’s published data. In

the absence of manufacturer’s data, use Table 2.

3.3.2 Electrical1. Compare bolted connection resistance values to values of similar connections.

Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.

2. Insulation-resistance values of bus insulation shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 3. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated. Dielectric withstand voltage tests shall not proceed until insulation-resistance levels are raised above minimum values.

3. If no evidence of distress or insulation failure is observed by the end of the total time of voltage application during the dielectric withstand test, the test specimen is considered to have passed the test.

4. Minimum insulation-resistance values of control wiring shall not be less than two megohms.

5. Results of electrical tests on instrument transformers shall be in accordance with NETA Section 7.10.

6. Results of ground-resistance tests shall be in accordance with NETA Section 7.13.

7. Accuracy of meters shall be in accordance with NETA Section 7.11.

8. Control Power Transformers

i. Insulation-resistance values of control power transformers shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 3. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated.

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ii. Turns-ratio test results shall not deviate by more than one half percent from either the adjacent coils or the calculated ratio.

iii. Secondary wiring shall be in accordance with design drawings and specifications.

iv. Secondary voltage shall be in accordance with design specifications.

v. Control transfer relays shall perform as designed.

9. Voltage transformers

i. Secondary wiring shall be in accordance with design drawings and specifications.

ii. Secondary voltage shall be in accordance with design specifications

10.Current-injection tests shall prove current wiring is in accordance with design specifications.

11.Results of system function tests shall be in accordance with Section 8.

12.Heaters shall be operational.

13.Phasing checks shall prove the switchgear or switchboard phasing is correct and in accordance with the system design.

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Table 2: Bolt Torque Specifications for Electrical Connections

Table 2.1US Standard Fasteners i,ii

Heat-Treated Steel – Cadmium or Zinc PlatedGrade SAE 1 & 2 SAE 5 SAE 7 SAE 8Head

Markingsnone 3 radial lines 5 radial lines 6 radial lines

Min. Tensile Strength

64K(lbs/in2)

105K(lbs/in2)

133K(lbs/in2)

150K(lbs/in2)

Bolt Diameter(Inches)

Non LubricatedTorque (Pound-Feet)

1/4 4 6 8 85/16 7 11 15 183/8 12 20 27 307/16 19 32 44 481/2 30 48 68 749/16 42 70 96 1055/8 59 96 135 1453/4 96 160 225 2357/8 150 240 350 3801 225 370 530 570

i. Consult manufacturer for equipment supplied with metric fastenersii Table is based on national coarse tread pitch.


Silicon Bronze FastenersHead markings none none

Min. Tensile Strength 70K(lbs/in2)

70K(lbs/in2)


Non LubricatedTorque (Pound-Feet)

LubricatedTorque (Pound-Feet)

5/16 15 103/8 20 151/2 40 255/8 55 403/4 70 60


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Table 2: Bolt Torque Specifications for Electrical Connections


Aluminum Alloy FastenersHead markings none




5/16 103/8 141/2 255/8 403/4 60


Table 2.4US Standard Fasteners i, ii, iii

Stainless Steel FastenersHead markings none




5/16 153/8 201/2 405/8 553/4 70

i. Consult manufacturer for equipment supplied with metric fastenersii Table is based on national coarse tread pitch.iii Table applicable to bolts, cap screws, nuts, flatwasher, locknuts (alloy 18.8) and Belleville washer (alloy302)

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Table 3: Insulation Resistance Test Values Electrical Apparatus and Systems

Nominal Rating of Equipment

(ACV)

Minimum Test Voltage(DCV)

Recommended Minimum Insulation Resistance

(Ω)250 500 25 M600 1,000 100 M

1,000 1,000 100 M2,500 1,000 500 M5,000 2,500 1 G8,000 2,500 2 G15,000 2,500 5 G25,000 5,000 20 G

34,500 and above 15,000 100 Gi. Values are commended in the absence on a consensus standard for insulation resistance test.ii. See Table 4 for Temperature Correction factors..iii. Test results a dependent on temperature of the insulating material and humidy surrounding the insulating material at the time of the test.

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Table 4: Insulation Resistance Conversion Factor (20ºC)

Temperature MultiplierºC ºF Oil Immersed Solid Insulation-10 14 .125 .25-5 23 .18 .320 32 .25 .405 41 .36 .5010 50 .50 .615 59 .75 .8120 68 1.00 1.0025 77 1.40 1.2530 86 1.98 1.5835 95 2.80 2.0040 104 3.95 2.5045 113 5.60 3.1550 122 7.85 3.9855 131 11.20 5.0060 140 15.85 6.3065 149 22.40 7.9070 158 31.75 10.0075 167 44.70 12.6080 176 63.50 15.8085 185 89.789 20.0090 194 127.00 25.2095 203 180.00 31.60100 212 254.00 40.00105 221 359.15 50.40110 230 590.00 63.20

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Table 5: Switchgear Withstand Test Voltages

Types of Switchgear

Rated Max Voltage(kV rms)

Maximum Test VoltagekV AC kV DC

MetalcladSwitchgear

4.76 14 208.25 27 3715.0 27 3727.0 45 † 38.0 60 †

Station-Type Cubicle

Switchgear

15.5 37 † 38.0 60 † 72.5 120 †

Metal-EnclosedInterrupterSwitchgear

4.76 14 208.25 19 2715.0 27 3715.5 37 5225.8 45 † 38.0 60 †

i. Derived from ANSI/IEEE C37.20.1-1993, Paragraph 5.5, Standard for Metal-Enclosed Low-Voltage Power Circuit- Breaker Switchgear, C37.20.2-1993, Paragraph 5.5, Standard for Metal-Clad and Station-Type Cubicle Switchgear and C37.20.3-1987 (R1992), Paragraph 5.5, Standard for Metal-Enclosed Interrupter Switchgear, and includes 0.75 multiplier with fraction rounded down.

ii. The column headed “DC” is given as a reference only for those using dc tests to verify the integrity of connected cable installations without disconnecting the cables from the switchgear. It represents values believed to be appropriate and approximately equivalent to the corresponding power frequency withstand test values specified for voltage rating of switchgear. The presence of this column in no way implies any requirement for a dc withstand test on ac equipment or that a dc withstand test represents an acceptable alternative to the low-frequency withstand tests specified in these specifications, either for design tests, production tests, conformance tests, or field tests. When making dc tests, the voltage should be raised to the test value in discrete steps and held for a period of one minute.

† Because of the variable voltage distribution encountered when making dc withstand tests, the manufacturer should be contacted for recommendations before applying dc withstand tests to the switchgear. Voltage transformers above 34.5 kV should be disconnected when testing with dc. Refer to ANSI/IEEE C57.13-1993 (IEEE Standard Requirements for Instrument Transformers) paragraph 8.8.2

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4. Test Set Operational Instruction Manual

15 KV Insulation Resistance Test set

AC High Potential Test set

DC High Potential Test set

Digital Low Resistance Test set

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5. Switchgear Commissioning Test Forms

Switchgear Inspection Form

Bus Resistance Test Form

Bus Insulation Resistance Test Form

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Switchgear Inspection Check List Form:

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Bus Section Resistance Test Form:

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Bus Insulation Test Form:

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6. References and Suggested Readings [1]. IEEE Std C37.20.2-1999

IEEE Standard for Metal-Clad SwitchgearCopyright © 2000 by the Institute of Electrical and Electronics EngineersInc.3 Park Avenue, New York, NY 10016-5997, USAISBN 0-7381-1829-X

[2]. ANSI/NETA ATS-2009, American National StandardStandard for Acceptance Testing Specification for Electrical Power Equipment and Systems© 2009, InterNational Electrical Testing Association

[3]. NFPA 70E, Elecrical Safety Requirements for Employee workplace 2009 Edition, Copyright © 2009 NFPA1 Batterymarch park, Quincy, Massachusetts 02169-7471, USA

[4]. A guide to Low Resistance TestingA Megger Publication

[5]. A Stitch in Time, The Complete Guide to Electrical Insulation TestingCopyright © 2006 Megger

[6] IEEE Standard 510 – 1983, Recommended Practice for Safety in High Voltage & High Power TestingCopyright © 2004 by the Institute of Electrical and Electronics EngineersInc.3 Park Avenue, New York, NY 10016-5997, USAISBN 1559378581

[7] NEMA Standard Publication SG 10 – 2008, Guide to OSHA and NFPA 70E Safety Requirements When Servicing and Maintaining Medium-Voltage Switchgear and Circuit Breakers Rated above 1000 Volts.

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module 2 commissioning switchgear assemblies

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