insulator-type-tests.pdf

7/28/2019 Insulator-Type-Tests.pdf

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TYPE TESTS ON DISC INSULATOR

UNITS & STRINGS


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TYPE TESTS ON DISC INSULATOR

UNITS & STRINGS

On single units

Sl

no

Nature of test Reference: standard/document

1 Verification of dimensions Approved drawing

Disc 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

383-1/935 Visible discharge & RIV

test

Powergrid approved GTP, IS 731/71 &

IEC 437/97

6 R id l t th IEC 797


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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 stringsused 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 specn

5 Mechanical strength test Powergrid tech specn

6 Vibration test Powergrid tech specn7 Power arc test IEC 1467

8 Artificial Pollution test

(only on anti fog discs)

IEC 507


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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 diameter

b) Unit spacing

c) Creepage distance

d) Verification of eccentricitye) Gauge check of socket cap & Ball pin

Disc diameter

a) Reference standard Approved drawing

a) Purpose/critically oftesting

Influences the creepage distance of the single unit andalso gap between insulator strings in case of double,

triple & quad strings

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


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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


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Creepage distance

a) Reference: standard Approved drawing


testing

Influences the electrical performance especially under

pollution

c) Test procedure Using adhesive tape the shortest distance between thesocket cap & pin is measured accounting only the

porcelain surface.

d) Acceptance criteria Normal disc

120 kN 315 mm + 60/- 0

160 kN 330 mm + 40/- 0

Anti fog

120 kN 430 mm + 60/- 0

160 kN 475 mm + 40/- 0

e) Instruments used

Steel scale & adhesive tape


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Radial & axial run out



testing

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 dia

Axial run out - < 4 % of disc dia

e) Instruments used Dial gauge


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Gauge check for ball & socket coupling

a) Reference standard IEC 120


testing

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


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2) Thermal Mechanical performance test

a) Reference standard Powergrid tech specn &

Cl 20 of IEC 383-1/93


testing

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 4cycles 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 ) h R i th t d EM t th


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TYPICAL LOAD & TEMPERATURE CURVE


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3) PF Voltage flashover & withstand test

Dry conditiona) Reference standard IEC 383-1

b) Purpose/critically oftesting

To verify the flashover & withstand voltage of the singleunit 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 kV

160 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


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4) Dry LI voltage flashover & withstand test

a) Reference standard IEC 383-1

b) Purpose/criticall

y of testing

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 samples

d) Acceptance

criteria

120 kN 110 kV/120 kV

e) Instruments

used

Impulse Generator

5) Visible discharge & RIV test

a) Reference standard IEC 60-1 & 437

b) Purpose/critically

of testing

To verify the specified test voltage

c) Test procedure The test is carried out on 3 samples

d) Acceptance Visible Discharge voltage > 18 kV


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f) Residual strength test



testing

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 themetal 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 )/R 0.65

e) Instruments used Tensile testing machine


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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


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Typical wave shape

Calculation of steepness

Steepness = Voltage/Raise time

Voltage = Y x Voltage scale x divider ratio x attenuation


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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


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TEST ON STRINGS WITH HARDWARE FITTINGS


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a. PF voltage withstand (Wet)

a) Reference standard Cl 10 of IEC 383-2


of testing

To verify the specified withstand voltage of the

insulator string

c) Test procedure In accordance with IEC

d) Acceptance

criteria

220 kV 460 kV, 400 kV - 680 kV

e) Instruments used PF Testing transformer

b. SI voltage withstand (Wet)

a) Reference standard Cl 11 of IEC 383-2


of testing

To verify the specified withstand voltage of the

insulator string under wet condition

c) Test procedure In accordance with IEC


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e) Instruments used Impulse Generator

d. Voltage distribution (Dry)

a) Reference standard Powergrid tech specn


of testing

To measure the distribution of voltage across an

energized disc insulator string

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

d) Acceptance

criteria

400 kV < 10 %

e) Instruments used PF Testing transformer, Calibrated spheres


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e. Radio Interference Voltage test



of testing

To measure the Radio noise generated by the test

sample when subjected to HV stress.

c) Test procedure IEC 60437

d) Acceptance

criteria

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

e) Instruments used PF Testing transformer, Coupling capacitor,

Radio noise meter

f. Corona test



of testing

To measure the Corona Inception & extinction

voltage on the test sample

c) Test procedure IS 731-1971

d) Acceptancecriteria

Extinction voltage > 320 kV for 400 kV strings

e) Instruments used PF Testing transformer, dark test hall


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h. Vibration test



of testing

To verify the performance of the insulator set

under Dynamic loading

c) Test procedure Powergrid spec

d) Acceptance

criteria

Shall withstand 10 million cycles of vibration

under specified conditions

e) Instruments used Vibration inducing equipment


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i. Power Arc test



of testing

To verify the performance of the insulator set

when subjected to Power Arcs

c) Test procedure IEC 1467

d) Acceptance

criteria

The 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


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j. Artificial Pollution withstand test



of testing

To verify the performance of the insulators under

polluted condition

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

d) Acceptance

criteria

The string shall withstand 3 voltage applications

at specified Pollution level & testing conditions

e) Instruments used PF testing transformer, Pollution chamber


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