funded by the european union comprehensive ......funded by the european union high pressure...

FUNDED BY THE EUROPEAN UNION

High Pressure Cogeneration for Sugar Sector in Pakistan

Comprehensive Technical Training

For Sugar Mills Staff on Operation & Maintenance of

Baggase Based HP Cogeneration System

Schedule: 10th July to 13th July, 2017



Power System Protection



Introduction to Protection

• Power system review• Protection system measures• Protection system components• Protection system purpose• Types of protective relays



Objectives

• Understand what protective relays are and how the basic types work

• Know the “terms” used in power system protection



Power System Elements

• Generators

• Transformers

• Power Lines

• Buses

• Medium Voltage Switchgear

• Capacitor Banks



Power System OverView



Single Supply • Multiple Supply

• Mobile Substations for emergencies• Types are defined by number of transformers, buses, breakers to provide adequate service for

application

Main Objectives

Power System Over View



Arrangement of Busbar


INDUSTRIAL SUBSTATION ARRANGEMENTS(Typical)



Power System Over View

Breaker-and-a-half –allows reduction of equipment cost by using 3 breakers for each 2 circuits. For load transfer and operation is simple, but relaying is complex as middle breaker is responsible to both circuits

Bus 1

Bus 2

Ring bus –advantage that one breaker per circuit. Also each outgoing circuit (Tx) has 2 sources of supply. Any breaker can be taken from service without disrupting others.

Arrangement of Busbar



SelectivitySpeed

SensitivityReliabilitySimplicityEconomy

Main Objectives

Power System Measures



• Measures of Performance• Sensitivity – ability of relay to

determine a faulted power system from a normal power system

• Selectivity – ability of a relay to determine what part of the power system is faulted



• Measures of Reliability• Dependability – ability of relay to

always trip for a fault in its protected zone

• Security – ability of relay to never trip for a fault outside its protected zone



• Speed – how fast can the relay determinethat there is a fault in its zone



Power System ProtectionRequirements

• Simplicity

• Economics• Protection costs• Equipment costs• Outage costs



Need of Protection

Protection system purpose

Protection system can not prevent system faults but it can limit the damage cause by short circuits.



Deals with the protection of electrical power systems from faults through the isolation of faulted parts from healthy electrical network

The objective of a protection schemes is to keep the power system stable by isolating only the

components that are under fault, whilst leaving as much of the network as possible still in

operation

General Overview

Power System purpose



Limits the damage caused by faultsProtect people and equipment from damage

Selectively clear faults in millisecondsProtecting equipment from overload

conditionsEnsure interruption to least number of

people

Necessity




Necessity

Protection System Purpose

In case of short circuit damage to the equipment is proportional to (If*t)

Where If is fault currentAnd t is the time of fault clearing

As If cannot be controlled easily therefore “t” must be minimised

Protection system helps in reducing this “t” to minimize damage



How to reduce this ‘t’

Protection System Purpose

By using fast relays

By using fast circuit breakers



Duties of Protection Engineer

Power System Purpose

Designs the protection systemSelects the proper and adequate protection

equipmentResponsible for installation, testing &

commissioningResponsible for maintenance

Keep a check on failures, assess cause and propose remedies



Generators TransformersTransmission Lines

General Overview

Components Of Power System



Basic Function

Instrument Transformer



Instruments used to step down voltage and current at suitable level

To isolate relaying system from actual power apparatus

This current and voltage is fed to protection relays for further monitoring and control

Basic Function




Two types of instrument transformers used:Current Transformer

Voltage(Potential) TransformerCTs are connected in series (1A, 5A)

PTs are connected in parallel(100V, 110V)

Basic Function




Electromechanical Relays

Static Relays

Numerical Relays

History

Protection Relays



A protection relay is a relay which responds to abnormal conditions in an electrical power

system, and controls a circuit breaker so as to isolate the faulty section of the system with the

minimum interruption to the service

Basic Idea

Protection Relays



Robust in useSlower in responseDifficult to installExpensiveLacks modern features like fault locator,telecommunication signals, reclosing etcNo memory to save fault recordsNot flexible in use

Electromechanical Relays

Protection Relays



High performanceSophisticated charactersticsCheaper than EM relaysFaster responseNot much robust comparing to EM relays

Static Relays

Protection Relays



Highly economicalContinuous self-monitoringMore reliableEasy to installMemory to save older fault recordsLot of modern fuctions available

Numerical Relays

Protection Relays



Characteristics Electromechanical Static NumericalSpeed of Response Slow Fast Very Fast

Timing Accuracy Temperature Dependent Temperature Dependent Stable

Size Bulky Small Very Compact

Draw Out Required Required Required Not Required

CT Burden High Low Low

Reset Time Very High Less Less

Functions Single Function Single Function Multi Function

Maintenance Frequent Frequent Very Low

Deteoriation due to Frequent Operations Yes No No

Reliability High Low High

Scada Compatibility No No Yes

Comparison

Protection Relays



To maintain the coordination in protection, concept of Zones are introduced

Each part in network is enclosed in a zoneZones are overlapped in order to have

backup protection

Basic Idea

Zones Of Protection



Basic Idea

Zones Of Protection



Overcurrent ProtectionDifferential Protection (Gen + T/F + Line)

Distance ProtectionUnder/Over Frequency Protection

Busbar Protection

Basic Idea

Types Of Protection



Commonly known as overcurrent & earth fault protection

Earliest protection being usedStill used as main and backup protectionWork on the simple principle of excess

currentRelay picks up when current exceeds

pickup value and send trip signal

Overcurrent

Types Of Protection



Overcurrent

Types Of Protection



Instantaneous overcurrent protectionDefinite time overcurrent protection

IDMT (Inverse Definite Minimum Time) over current protection

Directional overcurrent protection

Overcurrent

Types Of Protection



As a main protection in:11kV Feeders Protection

As backup protection in:Power and Auto Transformers

Transmission Lines

Overcurrent

Types Of Protection



Main protection is the essential protection provided for protecting an equipment

Main protection acts first and is primary line of defense

As a precautionary measure an additional protection is provided as Backup protection

It operates when first line of defence fails in any case

Main & Backup Protection

Types Of Protection



For 220kV and above transmission lines parallel protection is used to ensure the isolation of the

faultThey are fed from two different DC supply

sourcesParallel operation increases the probability of

discriminate tripping of the line

Parallel Protection

Types Of Protection



OC/EF Relay Spectrum

Types Of Protection



Basic Idea

Protection Of Transformers



Also called unit protectionBased on simple current comparison

If any difference occurs it will trip the breaker and isolate the transformer

Differential Protection




Act as main protection to:Power & Auto Transformers

MotorsGenerators

Whenever difference in current occurs relay send trip signal to both end breakers





Electrical ProtectionDifferential

Overcurrent/Earth Fault

Mechanical ProtectionBucholz Relay

Pressure relief device

Modes Of Protection




Winding




Idiff = |I1+I2|Irest = |I1| + |I2|

Where Idiff is Differential currentIrest is Restraining current

I1 & I2 are entering and leaving current





What is meant by Differential Protection


A relay that by its design or application is intended torespond to the difference between incoming andoutgoing electrical quantities associated with theprotected apparatus.The differential protection works as MAIN PROTECTIONfor transformers.

Current Input = Current Output

Protected Transformer



Numerical Relay Scheme




Winding & terminal faultsCore faults

Tank & transformer accessories faultsOn load tap changer faults

Abnormal operating conditions including external & through faults

Types of Faults




Winding or Inter turn faults develop rapidly into earth faults, and therefore only earth

fault protection is generally provided

Winding & Terminal Faults




Core Faults


• Due to excess eddy currents• Causes saturation of core resulting increase of

magnetizing current, thus increasing temperature



Leakage of oilSludge gathering in tank base

Reduces cooling thus increase in temperature

Tank Faults




Heavy duty tap changing can develop faults within their mechanism like shorts or flashovers etc

On Load Tap Changer Faults




OverloadingOvervoltage

Under frequencySystem fault surges

All causes increase in excitation current thus causing over heating

Abnormal Operating Conditions




Incipient faults below oil level resulting decomposition of oil

Buchholz Protection

Earth faults, phase to phase faults in main windings

Diff & OC/EF Protection

Saturation of core Over flux relay, Over voltage relay

Through faults OC Relay

Tank faults Oil level indicator & alarm

Overloads Thermal overload relay

System high surges Lightening arrestors

Tap changer faults Diff & OC/EF protection

Other Protections in Transformer




Differential Relay Spectrum




Testing of Transformers



Testing

Transformer tests:� The routine tests are carried out on all

transformers.� The type tests are carried out usually on

one unit only, in case of a multiple order, to verify the design.

� Special tests are carried out on customer request.

All transformer are tested according tocustomer requirements and last IEC60076, 60146, 60358 standards or ANSIstandards.

Testing of Power Transformer



Transformer routine tests:

� Winding resistance.� Voltage ratio and phase displacement.

� Short circuit impedance and load loss.

� No load losses and current.

� Dielectric routine test (according to IEC 60076-3).

� Test on OLTC where appropriate.

Transformer type tests:

� Temperature rise test.� Dielectric type tests (according to 60076-3).




Transformer special tests:

Dielectric special test (according to IEC 60076-3).

Determination of capacitances windings to earth and between windings.Determination of transient voltage transfer characteristic. Zero sequence impedance(s) on three phase transformers. Short circuit withstand test (according to IEC 60076-5). Determination of sound levels (according to IEC 60551).No load current harmonics. Auxiliary power consumption.

Measurement of the dissipation factor.




Routine tests:shall be made on every transformer to verify that the product meets the design specifications.

Design (type) tests:shall be made to determine the adequacy of the design of a particular type, style, or model of transformer or its component parts.

Design adequacy includes but is not limited to:meeting assigned ratings, operating satisfactorily under normal or special condition if specified, and compliance with appropriate standards of the industry.

Design tests are made on representative transformers to substantiatethe ratings assigned to all other transformers of basically the same design.




Other (type) tests:

Other tests are identified in individual product standards andmay be specified by the purchaser in addition to routine tests. (Examples: impulse, insulation power factor, audible sound, temperature rise, short circuit).




Dissolved Gas Analysis


•

• IEC 60599 1999 Mineral oil impregnated electrical equipment inservice – Guide to interpretation of dissolved and free gas analysis

•IEC 60422 Mineral oils in electrical equipment – Supervision andmaintenance guidance

C57.104-2008 IEEE Guide for the Interpretation of GasesGenerated in Oil Immersed Transformers



Dissolved Gas Analysis - History


Dissolved Gas Concentrations – C57.104-2008

Condition Hydrogen Methane Acetylene Ethylene Ethane Carbon Carbon TDGCb

Monoxide Dioxide

(H2) (CH4) (C2H2) (C2H4) (C2H6) (CO) (CO2)1 100 120 1 50 65 350 2500 720

2 101- 121- 2-9 51- 66- 351- 2500- 721-700 400 100 100 570 4000 1920

3 701- 401- 10-35 101- 101- 571- 4001- 1921-1800 1000 200 150 1400 10000 4630

4 >1800 >1000 >35 >200 >150 >1400 >10000 >4630



Basic Idea

Protection Of Transmission Lines



Primary Transmission Line (220kV)Secondary Transmission Line (132kV & 66kV)

Distribution Lines (11kV)

Voltage Levels used in KE




• Distance Protection• Line Differential Protection• Over current Protection• Breaker Failure Protection

Types




For 220kV and above transmission lines parallel protection is used to ensure the

isolation of the faultThey are fed from two different DC supply

sourcesParallel operation increases the probability

of discriminate tripping of the line

Concept Of Parallel Protection




The impedance/reactance of transmission line is proportional to its length

A relay capable of measuring the impedance/reactance upto a given point can be used to protect transmission lineThe relay compares the current flowing

and the voltage at relay point

Distance Protection




In case of fault on transmission line, the current flowing to fault point increases &

the voltage at relay point decreasesThe relay see this as fall in impedance & if this is below a pre-fixed setting, the relay

operates

Distance Protection




Type of Faults




WHAT IS MEANT BY ZONES IN DISTANCE PROTECTION? ?



Impedance TypeReactance Type

Mho Type

Distance Relay Types




Used to increase coordination between relaysA telecommunication line is used for

communication between relaysUse to decrease tripping time from both ends

PLC Schemes




DIT (Direct Inter Trip)Permissive Intertrip Overreaching

Step Acceleration (Reach Extention)

PLC Schemes




In this scheme, the relay having a fault in its Zone-1 trips and send trip signal to remote

end.Remote end breaker trips only if the distance

relay picked in Zone-2

Intertrip Schemes




The two relays are set at about 120% of the length of lineThe tripping is allowed only on the receipt of trip signal

from remote endAlso known as Directional Comparison Scheme

Permissive Intertrip




The relay trips the local breaker on a fault in its zone-1 & send the signal to remote end

On receipt of signal, the remote end Distance relay extend its zone-1 reach from 85% to 120%

of the length of line

Step Acceleration




Works on principle of Difference Current

In simple words: A Line Differential Relay monitors

Input Current = Output Current

Line Differential Relay




• Although routine testing has been carried out by utility Engineers at regular intervals, high voltage circuit breakers can fail to open when trip command is issued by protective relay

• To avoid huge damage, all the circuit breakers feeding the fault are tripped after the elapsed of certain fixed time by the relay. Relay is called “Breaker Failure relay”

Basic Idea

Breaker Failure Relay



Becomes necessary when two system/line merge in one busbar

The closing of breaker may be manual or through auto reclosing scheme

Parameters to be checked:Voltage

FrequencyPhase angle

Basic Idea

Synchrocheck Relay



80 to 90 % of faults on transmission lines are of transient nature as of insulator flashes

If line is tripped and time is allowed for the fault arc to de-ionize, reclosure of the circuit

breaker will result in the line being successfully re- energized

Auto- reclosure helps in improvement in continuity of supply

Basic Idea

Auto Reclosure Relay



Relay Function

Trip Circuit Supervision Operates when negative disappears

Tripping/Lock out Relay Operates to stop any other operation

DC Trip Unit Operates when DC disappears

Fault Locator Tell the possible location of fault

Misc. Protection

Other Relays



Generator Protection System



• Phase Faults• Ground Faults • Loss of Excitation • Over excitation • Overvoltage • Unbalanced Currents • Abnormal Frequencies • Motoring • Dead Machine• Breaker Failures

According to ANSI (American National Standard Institute)



• Differential Protection of Generator or Alternator. Any internal fault inside the stator winding is cleared by mainly differential protection scheme of the generator or alternator. The differential protections provided in the generator by using differential relay.

• Differential protection for a generator is mainly employed for the protection of stator windings of generator against earth faults and phase-to-phase faults. The stator winding faults are very dangerous, and it causes considerable damage to the generator. For the protection of stator winding of the generator, the differential protection system is used for clearing the fault in the shortest possible time for minimizing the extent of a damage.

Generator Differential Protection



• There are two sets of identical current transformers each set is mounted on either side of the stator phase windings. The secondary's of the current transformer are connected in star, and their end point is connected to the pilot wires. The relay coils are connected in star, their neutral points are connected to the common point of the current transformers neutral, and the outer ends one to each of three pilot wires.

• Setting of Generator Diff trip relay is 5% of the rated current 1705Amp

• If the 85.25 Amp difference create between both side CT's, the Generator breaker will be trip on diff protection




The relay is connected across equipotential points of the three wires so that the burden on each current transformer is same. The equipotential point of the pilot wire is its centre, so the relay is located at the midpoint of pilot wires.



• Consider an earth fault occurs on the phase R due to the breakdown of the insulation to earth. Due to the fault, the current in the secondary of the current transformers in phase R will become unequal. The difference of the two currents will flow through the corresponding relay coil, and it will give tripping command to the circuit breaker.




• When the machine delivering the equal currents in three phases, no unbalance or negative phase sequence current is produced as the vector sum of these currents is zero, when the generator is supplying an unbalanced load to a system, a negative phase sequence current is imposed on the generator. The system unbalance may be due to opening of lines, breaker failures or system faults.

• The negative sequence current in the stator winding creates a magnetic flux wave in the air gap which rotates in opposite direction to that of rotor synchronous speed.

Generator NEGATIVE SEQUENCE & Unbalanced loading



• This flux induces currents in the rotor body, wedges, retaining rings at twice the line frequency. Heating occurs in these areas and the resulting temperatures depend upon the level and duration of the unbalanced currents. Under these conditions it is possible to reach temperatures at which the rotor material no longer contain the centrifugal forces imposed on them resulting in serious damage to the turbine-generator set. Any machine as per design data will permit some level of negative sequence currents for continuous period.

Generator Unbalanced loading



Generator Unbalanced protection circuit Diagram



• The loss of excitation is the accidental loss of connectivity or DC supply voltage to the rotor field winding.

• This can be a disaster with violent vibrations (slipping a pole) or rotor heating (running as a synchronous machine).

• There is a special relay to protects again loss of excitation and disable the machine.

• In addition, if the field excitation circuit is disconnected suddenly, massive arcing will occur (due the high inductance of the field winding)

Loss of Excitation



• excitation in a generator. Failure of excitation that is failure of field system in the generator makes the generator run at a speed above the synchronous speed. In that situation the generator or alternator becomes an induction generatorwhich draws magnetizing current from the system. Although this situation does not create any problem in the system immediately but over loading of the stator and overheating of the rotor due to continuous operation of the machine in this mode may create problems in the system in long-run. Therefore special care should be taken for rectifying the field or excitation system of the generator immediately after failure of that system. The generator should be isolated from rest of the system till the field system is properly restored.

Loss of Excitation

http://www.electrical4u.com/alternator-or-synchronous-generator/

http://www.electrical4u.com/induction-generator/



Loss of excitation protection circuit Diagram



• Under frequency refers to a condition where the frequency of the AC supply drops to a value that is lower than its defined value such as 50 Hz or 60 Hz. Under frequency is usually caused by overloading a power source or problems with a prime mover such as engines or turbines.

The following are some of the effects of under frequency

High flux density in electric machinery, thereby causing higher magnetizing currents.

• High core loss and over-heating of the machines and possible failure.• Lower efficiency• Reduction in speed• The fault level increases due to reduced reactance

Under frequency situations can be avoided by the installation of under frequency relays which isolate systems and machinery in the event of an under frequency.

Under frequency protection



• over frequency occurs when the RPM of prime mover goes above the rated speed. This protection is basically for prime mover and gives a trip signal to the prime mover in case of over speed so that the centrifugal forces don't damage the prime mover and alternator rotor. This is generally a result of faulty speed governor or sudden throw off or throw in of large magnitude..

• Full or partial load rejection can lead to over speed of the generator, and hence, over frequency operation. In general, over frequency operation does not pose any serious problems and control action can be taken to reduce the generator speed and frequency to normal without tripping the generator. Generators are shipped with over speed detectors

Over frequency protection



• Generator overvoltage may occur during a load rejection or excitation control failure. In case of hydro generators, upon load rejection the generator may speed up and the voltage can reach high levels without necessarily exceeding the generator’s V/Hz limit. The overvoltage relay (59) is used to protect the generator from this condition.

• An over voltage on the terminals of the generator can damage the insulator of the generator, bus ducting, breakers, generator transformer and auxiliary equipment. Hence over voltage protection should be provided for machines of all sizes.

Over Voltage Protection



• Under voltage is defined as a condition where the applied voltage drops to 90% of rated voltage, or less, for at least 1 minute. Low-voltage conditions occur when a facility asks for more power than the line can deliver.

Under Voltage Protection



• Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of equipment. It generally operates instantly. Short circuit is a type of overcurrent. Magnetic circuit breakers, fuses and overcurrent relays are commonly used to provide overcurrent protection

Over Current protection



• Over fluxing is a dangerous situation in which the magnetic flux density increases to extremely high levels. The high flux density can induce excessive eddy currents in the windings and in other conductive parts inside the transformers.

• Hence it comes under electromagnetic device. It receives 3 phase ac electrical supply to its armature winding and DC supply is provided to rotor winding. Synchronous motor excitation refers to the DC supply given to rotor which is used to produce the required magnetic flux.

Over fluxing protection



• The generator will not develop output power when turbine input is less than the no load losses and motoring action develops on the turbine. The generator is able to generate power, usually 55 to 10% of generator capacity, within pre-determined time after closing of 220KV breaker.

Directional Power Protection Low Forward Power



• The Reverse power relay is used to protect a synchronous generator, running in parallel, from motoring. Motoring occurs due to the failure of the prime mover such as a turbine or an engine driving a generator that is connected to the grid. The generator which is running at the synchronous speed will continue to run at the same speed. However, the power required to keep the Gen running along with the prime mover will be drawn from the main, hence power flows in the reverse direction i.e. bus to generator. This condition is called reverse power.

• The reverse power relay operates by measuring the active component of the load current, I x cos φ. When the generator is supplying power, the I x cos φ is positive, in a reverse power situation it turns negative. If the negative value exceeds the set point of the relay, the relay trips the generator breaker after the preset time delay.

Directional Power Protection Reverse Active Power :



• When reverse reactive power occurs the outgoing current inthe particular alternator will go high and it will trip onovercurrent. Also this condition occurs when excitation ofthe subjected alternator fails when it is connectedparallel with other alternator or grid. Also this conditionoccurs when the rotating diode of alternator fails whenthem machine is running.

Directional Power Protection Reverse Reactive Power :



• The Rotor Protection relay is used in synchronous motors and generators to identify the presence of an earth fault in the rotor winding. While the winding in the rotor is insulated from the ground during normal operation, the Rotor is subjected to stresses due to vibration, heat, etc. These stresses can cause the winding to give way in a particular place and the winding can get earthed.

• Rotor Earth Fault recommend setting is

• 5000Ohm for • time:03 Sec

Rotor Earth Fault Protection



Rotor Earth Fault Protection



• While a single earthing in the winding is not immediately damaging. It sets the stage for damage if a second failure should occur. The second earthing can cause a short-circuit through the rotor causing extensive damage to the rotor and the winding.

The currents produced during a rotor earth fault can cause excessive vibration and disturb the magnetic balance inside the alternator. These forces can cause the rotor shaft to become eccentric and in extreme cases cause bearing failure.

Hence, it is necessary that any earthing in the rotor is detected at the earliest.

In slip ring rotors, carbon deposits on the slip rings may compromise the insulation resistance of the rotor. Hence, the slip rings need to be inspected for any deposits.

The Rotor Earth Fault Protection Device consists of a current injection device which applies an AC voltage to the rotor winding by means of a slip ring fitted on the rotor. The current is applied to the rotor through a coupling capacitor. In the normal condition, the system is floating and the current flowing through the device is zero as the resistance is high.

When a fault occurs, the current increases causing the relay to operate. The relay can be configured for alarm or trip depending on the criticality.



• It can provide complete ground fault protection during start-up, shutdown and even on turning gear and alternator dead condition. The scheme is normally taken out of service when the machine is offline for personnel safety, because the injected voltage is typically.

Dead Machine Protection



• This will operate when the fault current from the generator terminal becomes low with under voltage criteria

Voltage Restraint O/C protection



• Pole slip, also known as ‘out of step’ is a phenomenon caused either by low excitation, a faulty regulator or abrupt changes of load within the mains. It can cause severe mechanical stresses within the generator, putting winding at risk, causing shaft damage or adversely affecting the control operating system. Very high currents can cause thermal instability and ultimately lead to complete destruction of the generator and massive instability on the grid.

• Conventional protection, such as overcurrent, vector shift and ROCOF is not sufficient as it doesn’t respond quickly enough and is unreliable where large load jumps develop and cause oscillations.

POLE SLIPING Protection



Maintenance of Medium Voltage Switchgear



• Mechanical Checks and Visual Inspection:• Insulation Resistance Test:• Contact Resistance Test:• High Voltage Test

Tests to be carried Out



• Inspect switchgear and all components for any physical damage / defects.• Check nameplate information for correctness.• Inspect enclosures for proper alignment, foundation fixing, and grounding and vermin entry.• Inspect all covers, panels’ section and doors for paintwork and proper fit.• Check all the transport locks are removed.• Check for smooth and proper movement of racking mechanisms, shutter, rollers, rails and

guides.• Check proper alignment of the primary and secondary contacts.• Check operation of all mechanical interlocks.• Check tightness of all bolted connections.• Check for correct phasing connection of bus bar.• Perform mechanical check and visual inspection for breaker / Contactor as per section.• Perform mechanical check and visual inspection for instrument transformers as per section• Perform mechanical check and visual inspection on all disconnect / grounding switches as per

section.

Mechanical Checks and Visual Inspection:



• It includes panel enclosure, busbar, CT and circuit breaker. The following precautions should be taken care, before starting the testing. A visual inspection will be made to ensure the surface dust and moisture has been removed from the component under test. Ensure the component is isolated from other connected system, which may feed back to other components or circuits not under test.

• On testing, voltage shall be applied between one phase and other phases connected with ground, testing shall be repeated for other phases as mentioned above. Test voltage limits mentioned in table below:

Rated voltage Test voltage100-1000V AC/DC 1000V DC>1000 to <5000V AC 2500V DC> 5000V AC 5000V DC

Insulation Resistance Test

http://electrical-engineering-portal.com/how-low-voltage-air-circuit-breaker-works



• This test is to confirm the busbar joints are connected properly and verify the tightness.

• Note: The test shall be done with CBs inserted and closed. Measure the contact dc resistance between panels by injecting 100A DC. This will include busbar joint, CB contact resistance, CB cluster resistance, and CT primary resistance (if applicable).

Contact Resistance Test



• To determine the equipment is in proper condition to put in service, after installation for which it was designed and to give some basis for predicting whether or not that a healthy condition will remain or if deterioration is underway which can result in abnormally short life.

High Voltage Test



Shunt Capacitor



• Compensate the effect of capacitive currents• Shunt Capacitors raise the system voltage• During heavy load periods, shunt capacitors

are used to maintain the system voltage

Shunt Capacitor Bank



To provide local voltage support• Banks are switched when voltage falls below a set

• value. (15 -20 sec)• To provide system voltage support for higher power transfer• To Provide fast switching to prevent voltage collapse or voltage

excursions

Application of Shunt Capacitor Banks



System protection

Bank Protection

73

Protection Considerations



to protect the capacitor bank from stresseswhich may be caused by the system,

to protect the substation and system fromstresses which may be caused by the operation of the capacitor bank

74

System Protection



Reference - NEMA CP1-2000 and IEEE 1036

75

MIP

SYCO

N_2

015

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Capa

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Voltage(Percentage of Rated)

Duration

110% Continuous125% 30 minutes130% 1 minute140% 15 seconds170% 1 second200% 15 cycles220% 6 cycles

Capacitor Unit Over Voltage Limit



Bank Protection

Faulty Capacitor Unit or shorted elementsContinuous overvoltage on capacitorelements or units due to faulted elementsor fuse operations within the bank.

External arcing may cause case ruptures or other damage to capacitor units and may blow fuses.

76

Bank Protection



Time overcurrent - P.U.: 135% of nominalphase current for grounded wye banks or 125%for ungrounded banks. Extremely inversecharacteristic is used. Instantaneous - set at three to four times the

• Provides protection against major faults• Nominal phase current to override back to back inrush during

switching

.

Over Current Relays



• The capacitor bank is disconnected (tripped) ifthe system voltage exceeds 110% of thecapacitor bank rated voltage. This preventsfailure of capacitor bank.If the 110% value higher than the max. Systemvoltage ( 121 kV for 115 kV, 72.5 kV for 69 kV

•

system), then the capacitor bank is also trippedif the system voltage exceeds the max.Permissible system voltage. This protects otherequipment in the substation.

91

Overvoltage Protection



Phase Current Pick up: 50% of the capacitor banknormal rated current.

3

Bank Breaker Failure Protection



Capacitor Bank – Fuseless or externally fused- 59N – Simple overvoltage relay or

unbalance/ capacitor control relay- Additional PT and a switching device (circuit breaker) are required if capacitors are switched in and out for voltage control. 94

MIP

SYCO

N_2

015

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Neutral Unbalance Relay Used for Grounded Y Capacitor

Bank



Questions & Answers

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