TESTING OF SWITCHGEAR

SWITCH GEARSWITCH GEAR

Circuit BreakerCircuit Breaker Busbars and associated Insulators.Busbars and associated Insulators. Isolators/ DisconnectorsIsolators/ Disconnectors Instrument Transformers Instrument Transformers Protective Relays and auxiliary circuitsProtective Relays and auxiliary circuits

SWITCHGEAR TESTINGSWITCHGEAR TESTING

Developmental TestDevelopmental Test Type TestType Test Routine TestRoutine Test Factory Inspection TestFactory Inspection Test Pre-Commissioning TestPre-Commissioning Test

Developemental TestDevelopemental Test

Carried out on components,sub-assemblies Carried out on components,sub-assemblies and complete switchgear during and after and complete switchgear during and after the development of switchgear.the development of switchgear.

Related with R&Ds and manufacturing Related with R&Ds and manufacturing processes.processes.

Not covered under any reference standard.Not covered under any reference standard.

Type TestType Test

These tests are carried out for the purpose These tests are carried out for the purpose of proving characteristics of switchgear and of proving characteristics of switchgear and control gear, their operating devices and control gear, their operating devices and auxiliary equipment. auxiliary equipment.

The type tests are carried out on a The type tests are carried out on a maximum of four test specimen unless maximum of four test specimen unless otherwise specified in the relevant IEC otherwise specified in the relevant IEC standards. standards.

Type TestType Test

Lightning Impulse TestLightning Impulse Test Switching Impulse TestSwitching Impulse Test Power Frequency Over Voltage Withstand TestPower Frequency Over Voltage Withstand Test Partial Discharge TestPartial Discharge Test Artificial Pollution TestArtificial Pollution Test Temperature Rise TestTemperature Rise Test Resistance Measurement of the Main Circuit.Resistance Measurement of the Main Circuit. Short Time Withstand Current Test, Peak Withstand Short Time Withstand Current Test, Peak Withstand

Current TestCurrent Test Making Current and Breaking Current TestMaking Current and Breaking Current Test Mechanical Endurance TestMechanical Endurance Test

Lightning Impulse TestLightning Impulse Test

The insulation of switchgear should be so The insulation of switchgear should be so designed that it can withstand the occasional designed that it can withstand the occasional Lightning surges of high peak value, sharp rate of Lightning surges of high peak value, sharp rate of rise and short duration. rise and short duration.

The lightning impulse voltage withstand level of The lightning impulse voltage withstand level of the switchgear is proved by conducting this test.the switchgear is proved by conducting this test.

The test is performed with voltages of both The test is performed with voltages of both positive and negative polarity with respect to positive and negative polarity with respect to earth using the standard Lightning Impulse earth using the standard Lightning Impulse 1.2/501.2/50µs waveform (Fig 1).µs waveform (Fig 1).

Lightning Impulse TestLightning Impulse Test

Rated Voltage (KVrms) Rated Lightning Impulse Test Voltage (KVpeak)

3.6 40

7.2 60

12.0 75

36.0 170

145.0 650

245.0 1050

Brief test procedure

The standard test involves the application of 15 nos. of test voltages(1.2/50microsec lightning impulse wave surge to simulate lightning stroke condition) between each phase and earth in turn with CB closed & other phases earthed. In addition, test voltages are also applied across each set of open CB contacts. The overall test is considered to be satisfactory if not more than 2 flashovers occur during any series of 15 tests provided that these discharges only occur in self-restoring insulation (i.e. air, oil or SF6 gas). A breakdown of solid insulation normally results in an inability to recover and constitutes a test failure.

BASIC CIRCUIT FOR IMPULSE BASIC CIRCUIT FOR IMPULSE GENERATORGENERATOR

Switching Impulse TestSwitching Impulse Test

The purpose of this test is to verify the The purpose of this test is to verify the ability of the insulation of switchgear to ability of the insulation of switchgear to withstand the occasional high frequency withstand the occasional high frequency Switching surges occurred during opening Switching surges occurred during opening & closing of unloaded EHV AC lines, & closing of unloaded EHV AC lines, switching of small inductive or capacitive switching of small inductive or capacitive loads etc.loads etc.

This test is necessary for switchgear of This test is necessary for switchgear of rating 300 KV and above.rating 300 KV and above.

The switching surges are simulated in test The switching surges are simulated in test laboratories by a representative 250/2500 µs laboratories by a representative 250/2500 µs switching impulse wave obtained from an switching impulse wave obtained from an impulse generator.impulse generator.

The test procedure of switching impulse is The test procedure of switching impulse is same as that of Lightning Impulse Test.same as that of Lightning Impulse Test.

Power Frequency Over voltage Power Frequency Over voltage Withstand TestWithstand Test

The purpose of this test is to verify the The purpose of this test is to verify the ability of the insulation of switchgear to ability of the insulation of switchgear to withstand the temporary power frequency withstand the temporary power frequency over votages for a specified short duration.over votages for a specified short duration.

These over voltages of 50Hz waveform are These over voltages of 50Hz waveform are produced by sudden load-throw-off, faults, produced by sudden load-throw-off, faults, resonance, and poor voltage regulations by resonance, and poor voltage regulations by OLTC of transformers etc.OLTC of transformers etc.

Test procedureTest procedure

Main CircuitMain Circuit

The switchgear is subjected to the withstand level The switchgear is subjected to the withstand level of the power frequency high voltage for 1 min. of the power frequency high voltage for 1 min. (with respect to earth and between poles) (with respect to earth and between poles)

The result will be satisfactory if no failure occur. The result will be satisfactory if no failure occur. The withstand voltage levels for different ratings The withstand voltage levels for different ratings

of breakers are given below.of breakers are given below.

Rated Voltage (KVr.m.s)

Rated Power Frequency Test Voltage (KVrms)

3.6 10

7.2 20

12.0 28

36.0 70

145.0 275

245.0 530

On Auxiliary & Control CircuitsOn Auxiliary & Control Circuits

Auxiliary and control circuits of switchgear shall be Auxiliary and control circuits of switchgear shall be subjected to power frequency voltage withstand test subjected to power frequency voltage withstand test in accordance with IEC 61180-1. in accordance with IEC 61180-1.

The test is performed between the auxiliary and The test is performed between the auxiliary and control circuits connected together as a whole and control circuits connected together as a whole and the frame of the switching device.the frame of the switching device.

The test voltage is 2 KV with duration of 1 min. The test voltage is 2 KV with duration of 1 min. The auxiliary and control circuits of switchgear are The auxiliary and control circuits of switchgear are

considered to have passed the tests if no disruptive considered to have passed the tests if no disruptive discharge occurs during test.discharge occurs during test.

Partial Discharge TestPartial Discharge Test

The primary reason of this test is to check the The primary reason of this test is to check the healthiness of insulation of switchgear .healthiness of insulation of switchgear .

Main cause of PD is the formation of localised void in Main cause of PD is the formation of localised void in the insulation.the insulation.

The applied power frequency voltage is raised to a pre-The applied power frequency voltage is raised to a pre-stress value which is identical to the power frequency stress value which is identical to the power frequency withstand voltage test and maintained at that value for withstand voltage test and maintained at that value for 1 min. Partial discharge occurring during this period is 1 min. Partial discharge occurring during this period is disregarded. Then the voltage is decreased to a specific disregarded. Then the voltage is decreased to a specific value defined in the table below depending upon the value defined in the table below depending upon the configuration of equipment and system neutral for configuration of equipment and system neutral for partial discharge measurement.partial discharge measurement.

The maximum permissible The maximum permissible partial discharge level shall partial discharge level shall not exceed 5 pC. not exceed 5 pC.

However some equipment in However some equipment in sw. gear like Voltage sw. gear like Voltage Transformer have an Transformer have an acceptable level of PD greater acceptable level of PD greater than 5 pC. than 5 pC.

Any sub-assembly Any sub-assembly containing such components containing such components shall be considered acceptable shall be considered acceptable if the discharge level does not if the discharge level does not exceed 10 pc, but in that case exceed 10 pc, but in that case these will be tested for PD these will be tested for PD separately.separately.

Artificial Pollution TestArtificial Pollution Test

These tests are intended to provide information on the behaviour of These tests are intended to provide information on the behaviour of external insulations under conditions representative of pollution in external insulations under conditions representative of pollution in service.service.

   No artificial pollution tests are necessary when the creepage distances No artificial pollution tests are necessary when the creepage distances

of the insulators comply with the relationship given below :of the insulators comply with the relationship given below : It = a x If x Ur x KDIt = a x If x Ur x KD Where, It = minimum nomianl creepage distance in mmWhere, It = minimum nomianl creepage distance in mm a = application factora = application factor If = minimum nominal specific creepage distance (mm/kV)If = minimum nominal specific creepage distance (mm/kV) Ur = Rated voltage of switchgear in KVUr = Rated voltage of switchgear in KV KD= Correction factor due to diameterKD= Correction factor due to diameter

Temperature Rise TestTemperature Rise Test

Temperature rise test is performed to prove that temperature rise comply to limits specified in standards and to derive thermal characteristic of the transformer.

Temperature Rise TestTemperature Rise Test

The test is done with the normal rated The test is done with the normal rated sinusoidal current with the three poles sinusoidal current with the three poles connected in series. Temperature rise test is connected in series. Temperature rise test is carried out over a period of time sufficient carried out over a period of time sufficient for the temperature rise to reach a constant for the temperature rise to reach a constant value.When the steady temperature is value.When the steady temperature is reached the maximum temperature rise of reached the maximum temperature rise of each part should be less than the each part should be less than the permissible limits as per IS. permissible limits as per IS.

Resistance measurement Resistance measurement of Main Circuitof Main Circuit

Measurement of resistance of Main Circuit Measurement of resistance of Main Circuit is made for comparison between Sw. Gear is made for comparison between Sw. Gear type tested for temperature rise and sw. type tested for temperature rise and sw. gears of the same type.gears of the same type.

The resistance is measured before and after The resistance is measured before and after temperature rise test and the readings in temperature rise test and the readings in these two conditions should not differ by these two conditions should not differ by more than 20%.more than 20%.

The resistance is measured by Millivolt The resistance is measured by Millivolt Drop Test Method. Drop Test Method.

The DC current should be more than 50A The DC current should be more than 50A and less than rated current of circuit and less than rated current of circuit breaker. breaker.

The resistance should be measured at The resistance should be measured at ambient air temperature.ambient air temperature.

Resistance measurement Resistance measurement of Auxilliary Circuitof Auxilliary Circuit

These test is intended to verify the contact These test is intended to verify the contact performance under extremely low voltage condition performance under extremely low voltage condition due to the reason that on auxilliary contact due to the reason that on auxilliary contact materials, oxidation may occur which results in an materials, oxidation may occur which results in an increased contact resistance or even no conduction increased contact resistance or even no conduction at very low voltage.at very low voltage.

One sample of each type of auxilliary contacts is One sample of each type of auxilliary contacts is inserted into a resistive load circuit through which inserted into a resistive load circuit through which flows a current of 10 mA when energised by a flows a current of 10 mA when energised by a source having an open circuit voltage of 6 V DC source having an open circuit voltage of 6 V DC with a relative tolerence of 0-15% and the resistance with a relative tolerence of 0-15% and the resistance is measured according to IEC 60512-2.is measured according to IEC 60512-2.

Rated Short Time Withstand Rated Short Time Withstand Current TestCurrent Test

DefDefn n :The r.m.s value of the current which :The r.m.s value of the current which the switchgear can carry in the closed the switchgear can carry in the closed position during a specified short time.position during a specified short time.

Routine TestRoutine Test

Tightness testTightness test Measurement of resistance of main Measurement of resistance of main

circuit of each pole circuit of each pole Power frequency voltage withstand test Power frequency voltage withstand test

on main circuit and auxiliary circuitson main circuit and auxiliary circuits Mechanical operating testMechanical operating test Design and visual checksDesign and visual checks Tests on auxiliary and control circuitsTests on auxiliary and control circuits

Tightness TestTightness Test

The purpose of tightness tests is to demonstrate The purpose of tightness tests is to demonstrate that the absolute leakage rate does not exceed the that the absolute leakage rate does not exceed the specified value of the permissible leakage rate. specified value of the permissible leakage rate.

The test shall be performed at normal ambient air The test shall be performed at normal ambient air temperature with the assembly filled at the temperature with the assembly filled at the pressure (or density) corresponding to pressure (or density) corresponding to manufacturer’s test practice.manufacturer’s test practice.

•Mechanical operating test

Mechanical operational tests are performed on switchgear at the following points:(a)   at specified max. supply voltages and gas pressure(if applicable)1.      five closing operations2.      five opening operations(b)   at specified min. supply voltages and gas pressure(if applicable)1.      five closing operations2.      five opening operations(c)  at specified rated supply voltages and gas pressure(if applicable)1.      five closing operations2.      five opening operations

Design and Visual CheckDesign and Visual Check

The switchgear and control gear shall be The switchgear and control gear shall be checked to verify its compliance with the checked to verify its compliance with the purchase specification.purchase specification.

Tests on Auxiliary and Control CircuitsTests on Auxiliary and Control Circuits

The tests includes :The tests includes :

(i) Inspection of auxiliary and control circuits(i) Inspection of auxiliary and control circuits

The nature of the materials, the quality of assembly, the The nature of the materials, the quality of assembly, the finish etc. shall be checked. The components for auxiliary finish etc. shall be checked. The components for auxiliary circuits inside enclosures shall be checked for proper circuits inside enclosures shall be checked for proper mounting.mounting.

..

(ii) Functional tests(ii) Functional tests

This test is necessary to verify proper functioning of This test is necessary to verify proper functioning of auxiliary and control circuits in conjunction with other auxiliary and control circuits in conjunction with other parts of switchgear. Operational tests on closing circuits parts of switchgear. Operational tests on closing circuits should be done satisfactorily within the range of 85%-should be done satisfactorily within the range of 85%-110% of normal rated voltage. Operational tests on 110% of normal rated voltage. Operational tests on Tripping circuits should be done satisfactorily within the Tripping circuits should be done satisfactorily within the range of 70%-110% of normal rated voltage. range of 70%-110% of normal rated voltage. Measurement of operating times of the switchgear Measurement of operating times of the switchgear (Closing, Tripping and close-open operation time) is also (Closing, Tripping and close-open operation time) is also done in functional testsdone in functional tests

Factory Inspection Test by ClientFactory Inspection Test by Client

During inspection at the manufacturing During inspection at the manufacturing works, sample tests are witnessed by client . works, sample tests are witnessed by client . The normal routine tests are conducted on The normal routine tests are conducted on sample switchgear. Additionally, client may sample switchgear. Additionally, client may ask for other tests also as per their ask for other tests also as per their requirement or they can ask for repeat test requirement or they can ask for repeat test on same switchgear on same switchgear

Pre Commissioning TestPre Commissioning Test

High voltage withstand test (HVAC)High voltage withstand test (HVAC) Resistance measurement testResistance measurement test Measurement of insulation resistanceMeasurement of insulation resistance of of

the auxiliary and control circuitthe auxiliary and control circuit Current Transformers ( all testsCurrent Transformers ( all tests ). ). Voltage Transformers ( all tests ).Voltage Transformers ( all tests ).

Current Transformer TestCurrent Transformer Test

IR measurement.IR measurement. Ratio Checking. Ratio Checking. Winding resistance measurement.Winding resistance measurement. Polarity TestPolarity Test . . Magnetizing Characteristic TestsMagnetizing Characteristic Tests..

Insulation Resistance Insulation Resistance MeasurementMeasurement

Insulation resistance of the CT secondary is Insulation resistance of the CT secondary is measured with the help of 1000V measured with the help of 1000V

Megger (Insulation Tester) with respect to Megger (Insulation Tester) with respect to Earth & in between different cores.Earth & in between different cores.

  

Ratio CheckingRatio Checking

The usual method is to apply test current to The usual method is to apply test current to the primary winding of CT close to rated the primary winding of CT close to rated primary current and measure the primary current and measure the magnitudes of primary and secondary magnitudes of primary and secondary currents with a low value of secondary currents with a low value of secondary burden.burden.

Ratio CheckRatio Check (Connection Diagram)(Connection Diagram)

Winding Resistance Winding Resistance MeasurementMeasurement

Secondary winding resistance of a CT is Secondary winding resistance of a CT is measured as per the circuit diagram given measured as per the circuit diagram given below.below.

Polarity TestingPolarity Testing

If at any instant, current is entering the If at any instant, current is entering the primary from P1 the current should leave primary from P1 the current should leave secondary from terminal marked S1. A set secondary from terminal marked S1. A set up shown in the figure tests wheather the up shown in the figure tests wheather the polarity markings with respect to the polarity markings with respect to the secondary are correct or not. (P1 should secondary are correct or not. (P1 should correspond to S1)correspond to S1)

Polarity TestPolarity Test

Magnetizing Characteristic TestMagnetizing Characteristic Test

Magnetizing current is measured for several Magnetizing current is measured for several secondary emfs. This is accomplished by applying secondary emfs. This is accomplished by applying appropriate voltage to the secondary winding, and appropriate voltage to the secondary winding, and measuring the current taken by secondary winding measuring the current taken by secondary winding under test. under test.

During the test the primary and other windings are During the test the primary and other windings are kept open circuited. kept open circuited.

The RMS value of the sinusoidal voltage of rated The RMS value of the sinusoidal voltage of rated frequency applied to the secondary winding which, frequency applied to the secondary winding which, when increased by 10%, causes the secondary when increased by 10%, causes the secondary magnetizing current to increase by 50% is called Knee magnetizing current to increase by 50% is called Knee Point Voltage (Vk).Point Voltage (Vk).

Magnetizing Characteristic TestsMagnetizing Characteristic Tests

Voltage TransformersVoltage Transformers

Measurement of IR Measurement of IR Ratio TestRatio Test Polarity TestPolarity Test Measurement of secondary winding resistanceMeasurement of secondary winding resistance Measurement of primary winding resistanceMeasurement of primary winding resistance Magnetizing CharacteristicsMagnetizing Characteristics & Over Voltage & Over Voltage

Withstand TestWithstand Test

Insulation Resistance Insulation Resistance MeasurementMeasurement

Measurement is done with a 1000V Megger to ascertain the insulation resistance of primary winding w.r.t earth isolating the intentional earthing, insulation resistance of secondary windings w.r.t earth and insulation resistance in between primary and secondary winding.

Ratio TestRatio Test

The ratio of VT is checked by applying variable The ratio of VT is checked by applying variable AC voltage to the secondary winding and AC voltage to the secondary winding and measuring its voltage reflection in the primary.measuring its voltage reflection in the primary.

Ratio Test Ratio Test (Back to Back connection of two VTs)(Back to Back connection of two VTs)

Polarity TestPolarity Test

Measurement of secondary Measurement of secondary Winding ResistanceWinding Resistance

Measurement of primary Measurement of primary Winding ResistanceWinding Resistance

Magnetizing CharacteristicsMagnetizing Characteristics & & Over Voltage Withstand TestOver Voltage Withstand Test

Magnetizing characteristic gives a clear picture of Magnetizing characteristic gives a clear picture of amount of magnetizing current drawn by secondary amount of magnetizing current drawn by secondary core and the secondary e.m.f up to which the core core and the secondary e.m.f up to which the core exhibits its magnetic properties. exhibits its magnetic properties.

The varying voltage is applied in the secondary of The varying voltage is applied in the secondary of VT keeping the primary winding open and is raised VT keeping the primary winding open and is raised upto 120% of the normal rated voltage (i.e. 120% of upto 120% of the normal rated voltage (i.e. 120% of 63.5 V) to ascertain that VT can withstand this 63.5 V) to ascertain that VT can withstand this overvoltage without any failure.overvoltage without any failure.

The magnetizing current drawn by the VT secondary The magnetizing current drawn by the VT secondary core is also noted for different applied voltages.core is also noted for different applied voltages.

Magnetizing CharacteristicsMagnetizing Characteristics & & Over Voltage Withstand TestOver Voltage Withstand Test

Questions ?Questions ?

Thank You.Thank You.