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Which of the following is correct with reference to phasing out test on transformers?
This test is carried out only on the 3Φ transformer to identify primary and secondary winding in the same phase.
This test is carried out both on 1Φ and 3Φ transformers to identify high-voltage winding.
This test is carried out only on 1Φ transformer to identify primary and secondary winding.
This test is carried out both on 1Φ and 3Φ transformers to identify the primary and secondary winding.
This test is carried out only on the 3Φ transformer to identify primary and secondary winding in the same phase.
The phasing out test is essential for 3-phase transformers to ensure that the windings of different phases correspond correctly before connecting them in parallel or to a 3-phase load. It specifically verifies that the primary and secondary terminals belong to the same phase and have the correct polarity to prevent short-circuit conditions.
IS 2026 (Part 1)
The phasing out test is essential for 3-phase transformers to ensure that the windings of different phases correspond correctly before connecting them in parallel or to a 3-phase load. It specifically verifies that the primary and secondary terminals belong to the same phase and have the correct polarity to prevent short-circuit conditions.
VAB=VA−VB
Vinduced=−NdtdΦ
The test involves applying a low-voltage AC supply to one winding and measuring the potential difference between terminals of the other windings. If the terminals are correctly phased, the voltmeter reading between corresponding points in different phases will be zero or within expected limits, confirming that the voltage vectors are in the same relative phase sequence.
Used to identify phase sequences in 3-phase banks.
Critical for preventing short-circuits during parallel operations.
Ensures correct polarity marks are observed.
Does not differentiate between primary and secondary voltage levels, only phase alignment.
Prevents catastrophic short circuits during commissioning.
Confirms correct internal connection of star or delta configurations.
Requires careful measurement to avoid induction hazards.
Not necessary for single-phase transformers where polarity test is sufficient.
Transformer installation and commissioning.
Parallel operation of 3-phase transformer banks.
Post-repair testing of transformer windings.
Option B and D are incorrect as primary and secondary identification for 1-phase transformers is done via simple continuity or polarity tests.
Phasing out is exclusively relevant when multiple phases must be synchronized, which is not applicable to individual single-phase transformers.
A is correct — This test is carried out only on the 3Φ transformer to identify primary and secondary winding in the same phase.
Always remember that 'phasing out' relates to 3-phase systems whereas 'polarity test' is the equivalent for single-phase transformers to identify terminal markings.
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