Testing Of Safety Devices And Auxiliaries

Testing Of Safety Devices And Auxiliaries

We have studied various testing methods for internal parts of transformer.

Transformer device is an important equipment in the electric-system of generating station, receiving station, substation etc.

It's normal working is most important for the continuity of supply. Oil testing, core testing, insulation resistance testing.

Following few paragraphs give an additional list of lasting of safety devices:

1)Test On Relays

The test are conducted by manufacturer at his works. The tests are also conducted at the user's premises (of work place) at the site while maintenance work is carried out.

The tests any (1) type tests (2) Routine tests.

As stated the tests are conducted. 

Before accepting by the user from manufacturer.

On site prior of commissioning. During periodic maintenance.

Quality of relay and reliability of operation of relay is very important.

Acceptance test : This test is performed in laboratories. For new relay intensive testing is carried out to check characteristics, reliability and prompt response in circuit disturbances. These test are performed in the presence of customer and represents of manufactures.

Installation Tests

These are the field tests. The aim of testing is to determine that the protection operates correctly in actual service.

Mostly these tests are simulating tests conditions by means of portable test sets.

Some other tests are :

✓ Using primary current injection

✓ System fault test

✓ Operating test with reduced voltage.

These are to be conducted on every new installation only.

Maintenance testing : Periodic maintenance schedule is followed for testing.

Repair tests : Some repair work is carried on site but some require laboratory for repairs.

Manufacture's test : These are type, routine and development tests. 

Testing Of Bushings

Tests on bushings can be classified as:

(I) Type Tests

1) Wet Power Frequency Voltage Withstand Test

These tests are applicable to outdoor, indoor and outdoor immersed bushings upto 245 kV ratings.
Duration of test is 60 seconds. The test is conducted in accordance with I.S.2071 (part 2) 1976.

Before the commencement of the test the bushings is exposed to the atmosphere condition specified in I.S. The bushings is considered to have passed the test if no flashover or puncture occurs. If there is puncture, the bushing is considered to be failed the test.

If flashover occurs the test is repeated only once. If during the repetition of the test, no flashover or puncture occurs the bushing is considered to have passed the test.

2) Lighting Impulse Voltage Withstand Test

This test is applicable to all types of tests.

It is conducted as per LS 2071 (Part 2) - 1976. The bushing is subjected to fifteen full wave impulse of positive polarity followed by fifteen full wave impulses of negative polarity of the standard wave form 1.2/50 Its. The time intervals between consecutive applications of the voltage is sufficient to avoid effects from the previous application of voltage.

The bushing in considered to have passed the test if no any puncture occurs and if the number of flashover at either polarity is not exceed two except for transformer bushings for not more than.

3) Dry Or Wet Switching Impulse Voltage Withstand Test

The bushing is subjected to fifteen impulses of positive polarity followed by fifteen impulses of negative polarity of the standard waveform 250/2500 µs.

The bushing is considered to have passed the test if no puncture occurs at either polarity and if the number of flashover at either polarity does not exceed two except the transformer bushings for which not more than two flashover at positive polarity and one flashover at negative polarity are permitted.

4) Temperature Rise Test

The bushing is considered to have passed the test if the permissible temperature rise limit specified as in LS. are met and if there is no visible evidence of damage.

(Ii)Routine Tests

1. Measurement of dielectric dissipation factor tan 8 and capacitance at ambient temperature.
2. Dray power frequency voltage withstand test
3. Measurement of partial discharge quantity.
4. Test on top insulation.