Insulator Type Tests

TYPE TESTS ON DISC INSULATOR UNITS & STRINGS

TYPE TESTS ON DISC INSULATOR UNITS & STRINGS

1.1) On single units

Sl no

Nature of test Reference: standard/document

1 Verification of dimensions Approved drawingDisc diameter - do -Unit spacing - do -Creepage distance - do -Radial & axial run out - do -

2 Thermal Mechanical performance test

Powergrid tech specn & Cl 20 of IEC 383-1/93

3 PF Voltage withstand and flashover test (Dry & Wet)

Powergrid approved GTP & Cl 20 of IEC 383-1/93

4 LI withstand and flashover test (Dry)

Powergrid approved GTP & Cl 20 of IEC 383-1/93

5 Visible discharge & RIV test

Powergrid approved GTP, IS 731/71 & IEC 437/97

6 Residual strength IEC 7977 Steep wave front test Powergrid tech specn8 Impact test Powergrid tech specn & ANSI C 29.2

1.2) On string with hardware fittings

Sl no

Nature of test Reference: standard/document

1 PF voltage withstand (Wet)

Cl 10 of IEC 383-2

2 SI voltage withstand (Wet) - only on strings used for 400 kV & above

Cl 11 of IEC 383-2

3 LI voltage withstand & flashover test (Dry)

Cl 9 of IEC 383-2

4 Voltage distribution Powergrid tech specn5 Mechanical strength test Powergrid tech specn

6 Vibration test Powergrid tech specn7 Power arc test IEC 14678 Artificial Pollution test

(only on anti fog discs)IEC 507

TYPE TEST PROCEDURE

TEST ON SINGLE UNITS

1) Verification of dimensions

Following physical dimensions shall be checked on 10 samples in accordance with the drawing approved by Powergrid. a) Disc diameterb) Unit spacingc) Creepage distance d) Verification of eccentricitye) Gauge check of socket cap & Ball pin

Disc diameter

a) Reference standard Approved drawing

a) Purpose/critically of testing

Influences the creepage distance of the single unit and also gap between insulator strings in case of double, triple & quad strings

b) Test procedure Check the outer diameter of disc & verify compliance with the drawing

c) Acceptance criteria 120 kN – 255 +/- 11mm, 160 kN & 210 kN 280 +/- 12 mm, 120 kN A/F – 280 +/- 12 mm, 160 kN A/F – 305 +/- 13 mm

d) Instruments used Out side caliper & scale

Unit spacing


b) Purpose/critically of testing

Influences the overall length of the string and hence the phase to ground clearances.

c) Test procedure Check the ball pin to ball pin distance of the single unit & verify compliance with the drawing

d) Acceptance criteria 120 kN – 145 +/- 4 mm, 160 kN & 210 kN 170 +/- 5 mm.e) Instruments used Marking block & vernier height gauge

Creepage distance

a) Reference: standard Approved drawing


Influences the electrical performance especially under pollution

c) Test procedure Using adhesive tape the shortest distance between the socket cap & pin is measured accounting only the porcelain surface.

d) Acceptance criteria Normal disc 120 kN – 315 mm + 60/- 0160 kN – 330 mm + 40/- 0Anti fog120 kN – 430 mm + 60/- 0160 kN – 475 mm + 40/- 0

e) Instruments used Steel scale & adhesive tape

Radial & axial run out



It is a measure of alignment of socket cap, porcelain and ball pin. Influences the mechanical strength of the unit

c) Test procedure The insulator is placed under light tension between suitably mounted coupling pieces. The two coupling pieces shall be on the same axis and shall be free to rotate. Two dial gauges are arranged as shown so that they make contact with the maximum diameter and at the tip of the outer most rib. The insulator is rotated through 360 deg and the max variation in the readings of the dial gauges is recorded.

d) Acceptance criteria Radial run out - < 3 % of disc diaAxial run out - < 4 % of disc dia

e) Instruments used Dial gauge

Gauge check for ball & socket coupling

a) Reference standard IEC 120


It is carried out to verify the compliance of the ball & socket coupling with relevant gauges.

c) Test procedure The socket cap & ball pin of the insulator shall be checked with the relevant standard calibrated ‘GO’ & ‘NOT GO’ gauges. The samples shall comply with the standard gauges.

d) Acceptance criteria Compliance with gaugese) Instruments used Standard Calibrated Gauges

2) Thermal Mechanical performance test

a) Reference standard Powergrid tech specn & Cl 20 of IEC 383-1/93


To check the mechanical performance of the samples under simultaneous tensile loading and extreme varying temperatures.

c) Test procedure This test is carried out on 20 samples. The test is carried out in a specially constructed thermal chamber. A tensile load equal to 70 % of the specified EM load shall be applied and the temperature inside the chamber shall be varied from – 30 deg to + 40 deg C in a duration of 24 hours. Minimum tensile load of 70 % shall be maintained through out the 24 hours duration and shall be released and reapplied after every 24 hours. After completing 4 cycles of 24 hours each, the tensile load shall be released & temperature brought down to the ambient and the units shall be subjected to EMS test. No failure during thermal cycles or during EMS test is permitted. After EMS test, Average (X) & Standard deviation (S) is calculated & statistically evaluated.

d) Acceptance criteria No failure during thermal cycles or during EMS test is permitted. The test results shall meet the following criteria. X ≥ (R + 3 σ) where R is the rated EM strength

e) Instruments used Thermal mechanical test M/c, Tensile testing M/c & PF transformer

TYPICAL LOAD & TEMPERATURE CURVE

3) PF Voltage flashover & withstand test

Dry conditiona) Reference standard IEC 383-1


To verify the flashover & withstand voltage of the single unit using PF voltage under dry condition

c) Test procedure The test is carried out on 3 samples. Voltage is applied to the ball pin of the insulator & the socket cap is earthed. 5 flashovers are applied & average value obtained. The voltage is reapplied and maintained at the specified value for a duration of 1 minute & no flashover is permitted during this interval.. The test values are corrected to the standard atmospheric condition. The value obtained shall be greater than the specified value

d) Acceptance criteria 120 kN – F/o >75 kV, W/s >70 kV160 kN – F/o >80 kV, W/s > 75 kV

e) Instruments used PF testing transformer & arrangement for suspending the insulator in vertical condition

Wet conditiona) Reference standard IEC 383-1


To verify the flashover & withstand voltage of the single unit using PF voltage under Wet condition

c) Test procedure The test is carried out on 3 samples. Water of specified resistivity & precipitation is sprayed on the test sample. After wetting the sample for 5 minutes Voltage is applied to the ball pin of the insulator & the socket cap is earthed. 5 flashovers are applied & average value obtained. The voltage is reapplied and maintained at the specified value for a duration of 1 minute & no flashover is permitted during this interval.. The test values are corrected to the standard atmospheric condition. The value obtained shall be greater than the specified value.

d) Acceptance criteria 120 kN – F/o >45 kV, W/s >40 kV160 kN – F/o >50 kV, W/s > 45 kV

e) Instruments used PF testing transformer, arrangement for suspending the insulator in vertical condition, Rain making equipment

4) Dry LI voltage flashover & withstand test

a) Reference standard IEC 383-1


To verify the flashover & withstand voltage of the single unit using LI voltage under dry condition

c) Test procedure The test is carried out on 3 samplesd) Acceptance

criteria120 kN – 110 kV/120 kV

e) Instruments used

Impulse Generator

5) Visible discharge & RIV test

a) Reference standard IEC 60-1 & 437


To verify the specified test voltage

c) Test procedure The test is carried out on 3 samplesd) Acceptance

criteriaVisible Discharge voltage > 18 kVRIV < 50 micro Volts

e) Instruments used PF testing Transformer, RIV meter

f) Residual strength test



Verification of the minimum mechanical strength of insulator stubs with out shed when used in string.

c) Test procedure This test shall be carried out on 25 samples. Samples shall be subjected to temperature cycle test as per IEC 383-1. The sheds shall be broken using hammer blows and no part of the broken shed shall be greater than the maximum diameter of the socket cap. The stubs shall then be subjected to tensile load applied between the metal fittings and value recorded. Average (X) & Standard deviation (S) of the test values shall be calculated and compared with the factor k (0.65)

d) Acceptance criteria (X – 1.645 σ)/R ≥ 0.65e) Instruments used Tensile testing machine

g) Steep Front Wave test

b) Reference standard

Powergrid technical specification

c) Purpose/critically of testing

To verify the puncture withstand capability of insulator in air when subjected to impulse voltage of high rate of raise.

d) Test procedure This test is carried out on 10 samples. Each insulator shall be subjected to 5 positive & 5 negative impulses with effective rate of raise of 2500 kV/micro sec. Subsequently the samples shall be subjected to PF flashover test under Dry condition.

e) Acceptance criteria

Average of 3 PF flashovers shall not be lesser than 95 % of the specified Dry PF flashover voltage. No puncture shall occur either during Impulse or PF voltage application

f) Instruments used LI generator, PF test transformer

Typical wave shape

Calculation of steepness

Steepness = Voltage/Raise time

Voltage = Y x Voltage scale x divider ratio x attenuation

Where Y is the peak value measured on oscillogramVoltage scale, divider ratio & attenuation depends on the measuring system

Raise Time = T x 2.5 x time scale Where T is time from 50 to 90 % measured on the oscilligram.2.5 is the factor to get 100 % time. Time scale depends on the measuring system.

h) Impact test

i) Reference standard

Powergrid tech specn & ANSI C 29.2

j) Purpose/critically of testing

To verify the withstand capability of insulator shed when subjected to mechanical impact.

k) Test procedure 3 samples shall be subjected to specified Impact load applied to the outer most rim of the insulator. No breakage of the insulator shed is permitted. Subsequently the samples shall also pass PF frequent flashover test. No puncture shall occur during flashover test.

l) Acceptance criteria

7 N-m for up to 120 kN. 10N-m for above 160 kN disc insulators

m)Instruments used Impact testing machine & PF test transformer

TEST ON STRINGS WITH HARDWARE FITTINGS

a. PF voltage withstand (Wet)

a) Reference standard Cl 10 of IEC 383-2


To verify the specified withstand voltage of the insulator string

c) Test procedure In accordance with IECd) Acceptance

criteria220 kV – 460 kV, 400 kV - 680 kV

e) Instruments used PF Testing transformer

b. SI voltage withstand (Wet)



To verify the specified withstand voltage of the insulator string under wet condition


criteria400 kV - 1050 kVp

e) Instruments used Impulse Generator, Rain making equipment

c. LI voltage withstand test (Dry)



To verify the specified withstand voltage of the insulator string


criteria400 kV - 1450 kVp

e) Instruments used Impulse Generator

d. Voltage distribution (Dry)

a) Reference standard Powergrid tech specn


To measure the distribution of voltage across an energized disc insulator string

c) Test procedure Sphere gap method, % VD = E/Vn x 100d) Acceptance

criteria400 kV < 10 %

e) Instruments used PF Testing transformer, Calibrated spheres

e. Radio Interference Voltage test



To measure the Radio noise generated by the test sample when subjected to HV stress.

c) Test procedure IEC 60437d) Acceptance

criteriaNoise level < 60 dB @ 305 kV for 400 kV strings

e) Instruments used PF Testing transformer, Coupling capacitor, Radio noise meter

f. Corona test



To measure the Corona Inception & extinction voltage on the test sample

c) Test procedure IS 731-1971d) Acceptance

criteriaExtinction voltage > 320 kV for 400 kV strings

e) Instruments used PF Testing transformer, dark test hall

g. Mechanical strength



To verify the Mechanical strength of the insulator set under tensile load

c) Test procedure Powergrid specd) Acceptance

criteriaDepends on the insulator rating

e) Instruments used Tensile testing machine

h. Vibration test



To verify the performance of the insulator set under Dynamic loading

c) Test procedure Powergrid specd) Acceptance

criteriaShall withstand 10 million cycles of vibration under specified conditions

e) Instruments used Vibration inducing equipment

i. Power Arc test



To verify the performance of the insulator set when subjected to Power Arcs

c) Test procedure IEC 1467d) Acceptance

criteriaThe string shall not separate after subjected to 3 shots of 40 kA for a duration of 0.2 s, 0.2 s & 0.5 s. Subsequently the string shall withstand 80 % of the rated tensile load

e) Instruments used Short circuit generator

j. Artificial Pollution withstand test



To verify the performance of the insulators under polluted condition

c) Test procedure IEC 507, Salt fog Method & Clean fog methodd) Acceptance

criteriaThe string shall withstand 3 voltage applications at specified Pollution level & testing conditions

e) Instruments used PF testing transformer, Pollution chamber

Insulator Type Tests

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