May 9, 2022

Simple ageless methods for field testing power transformers of no-load condition at the low induced voltage – Part III

After the end of the war in 1945, the transformer industry in the Soviet Union developed at a faster pace.

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(Analytical review with the aid of transformer field service technicians)

After the end of the war in 1945, the transformer industry in the Soviet Union developed at a faster pace than the production of synchronous three-phase generators of sufficient power to test power transformers.

The MTZ test station had only a single-phase generator, and A. K. Ashryatov proposed a simplified method for determining the no-load losses of a three-phase transformer at a reduced voltage of 5–10 % of the nominal, followed by recalculation to the nominal voltage. It was proposed to carry out three experiments, in each of which power from a single-phase generator is supplied to two phases, and the third phase is short-circuited. The sought value of the losses at the rated voltage was determined from the half-sum of the losses in these three experiments using a special formula [23, 24]. This method became widespread as the “Ashryatov test” was included in GOST 3484-55 and survived in GOST 3484-65. Note that GOST 3484-55 also contained a three-phase experiment at reduced voltage, but in practice, it did not become widespread and was excluded from further editions of this standard.

In subsequent years, new data on the comparison of losses at low and rated voltage showed an unacceptably large spread when using the conversion formulas, and the conversion was excluded from GOST 3484-77 [25]. But the measurement of losses at low voltage as a comparison method is preserved in the current standard GOST 3484.1-88. According to the standard for general requirements for transformers [26], this test is included in the scope of the factory routine tests of transformers 10 MVA and above.

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