INSTRUMENT TRANSFORMERS TESTS (VOLTAGE AND CURRENT TRANSFORMERS) TUTORIALS

These are the routine, type, and other tests that are necessary to assure that the design and construction of the transformer are adequate to meet the specified requirements.

Routine Tests
Each instrument transformer shall receive the following routine tests at the factory. These tests shall be made on the instrument transformer after complete assembly, where feasible.

a) Applied voltage dielectric tests between windings and between windings and ground (with the exception there is no primary insulation test for bushing type, split-core, or any current transformer designed with incomplete insulation for the primary conductor)
b) Induced voltage tests
c) Accuracy tests
d) Polarity test

Type Tests (design tests)
Type tests shall be performed on at least one transformer of each design group that may have a different characteristic in the specific test. Transformers subjected to type tests shall withstand the applicable routine tests before and after the type tests. It is not necessary to conduct more than one type test on the same unit.

Type tests for voltage transformers shall include:
a) Impulse (BIL) test
b) Wet 60 Hz 10 s withstand test
c) Short-time mechanical withstand test
d) Temperature rise test to verify the rating factor
e) Accuracy test to verify quoted accuracy ratings

Type tests for current transformers shall include:
a) Impulse (BIL) test
b) Wet 60 Hz 10 s withstand test
c) Short-time mechanical current rating test
d) Temperature rise test to verify the thermal burden rating
e) Accuracy test to verify quoted accuracy ratings
f) Switching impulse test, if applicable

Other Tests
Other tests are additional tests made for application information, for provision of specific data requested by users, for verification of type capability, etc. Examples of other tests are:

a) Special accuracy tests
b) Open-circuit secondary voltage magnitude or withstand capability on current transformers
c) Voltage transformer capabilities in respect to 125%, 140%, and 173% overvoltage characteristics required
d) Radio influence voltage test (RIV)
e) Partial discharge test

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