1. Why power transformer testing?
Tests serve as an indication of the extent to which a transformer is able to comply with a customer’s specified requirements; for example:
lLoading capability
lDielectric withstand voltage test
lFurther operating characteristics
Tests are also part of a manufacturer’s internal quality assurance program. A manufacturer’s own criteria have to be fulfilled in addition to requirements specified by customers and applicable standards.
Differing requirements are generally combined and published in national and international standards. The primary Standards organizations are IEC and ANSI. These standards are often used directly to develop national standards. IEC is the abbreviation for International Electro-technical Commission and ANSI stands for American National Standard Institute, Inc
In the electric area, ANSI has to a great extent delegated the writing and publication of standards to IEEE, the Institute of electric and Electronics Engineers, Inc.
2. Types of tests
The IEC 60076-1 [1] and IEEE Std C57.12.00 [50] Standards distinguish between the following types of tests:
l Routine tests
l Type- or design1 tests
l Special- or other1 tests
Routine tests:
Routine tests are tests required for each individual transformer.
Typical examples:
DC winding Resistance measurements, voltage ratio test, load loss and none-load measurements, etc.
Type- or design tests
Type or design1 tests are conducted on a transformer which is representative2 of other transformers, to demonstrate that these transformers comply with specified requirements not covered by routine tests.
Typical example:
Special- or other tests
Special- or other1 tests are tests other than type- or routine tests agreed to by the manufacturer and the purchaser.
Typical example:
Measurement of zero-sequence impedance, sound level measurement, etc.
Note:
Depending on the respective standard and the maximum system voltage, certain dielectric tests, such as lightning impulse voltage tests, for example, may either be routine tests, type tests or special tests. The same is true for switching impulse voltage test.
Prower transformer related testings:
nMeasurement of winding resistance
nVerification of voltage ratio and vector group or phase displacement
nMeasuring the short-circuit voltage impedance and the load loss
nMeasuring the no-load loss and no-load current
nSeparate source AC withstand voltage test or Applied voltage test
nInduced voltage tests
nPartial Discharge Measurements
nLightning impulse and switching impulse test
nTemperature rise test
nMeasurement of zero-sequence impedance(s) on three-phase transformers
nShort-circuit withstand test
nSound level measurement
nTest on on-load tap-changers and dielectric tests on auxiliary equipment
nMeasurements of the harmonics of the no-load current
nMeasurement of insulation resistance
nMeasurement of dissipation factor (tanδ) of the insulation system capacitances