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Which of the following is NOT correct with reference to delta-star type distribution transformers application?
In delta-star type transformer, secondary voltage is in phase with the primary voltages.
In delta-star type transformer, fault protection is one of the primary advantages.
In delta-star type transformer, no distortion is produced by third harmonic components.
In delta-star type transformer, large, unbalanced loads can be handled without any difficulty.
In delta-star type transformer, secondary voltage is in phase with the primary voltages.
In a Delta-Star (╬ФтИТY) transformer connection, a phase shift of 30┬░ is introduced between the primary and secondary line voltages. Therefore, the secondary voltage is not in phase with the primary voltage, making option A the incorrect statement.
IS 2026 Part 1
In a Delta-Star (╬ФтИТY) transformer connection, a phase shift of 30┬░ is introduced between the primary and secondary line voltages. Therefore, the secondary voltage is not in phase with the primary voltage, making option A the incorrect statement.
╬╕=30┬░ тАФ Phase shift angle between primary and secondary line voltages in ╬ФтИТY connection
VPтАЛVLтАЛтАЛ=3тАЛ тАФ Line to phase voltage ratio in Star connection
The phase shift occurs because the star-connected secondary windings have voltages that are the phasor sum of the delta-connected primary windings. Due to the transformer winding orientation and connection standard, the secondary line voltage leads or lags the primary line voltage by 30┬░ depending on the vector group (e.g., Dyn11 or Dyn1).
Delta-Star connections provide a neutral point for grounding and single-phase loads.
The delta winding provides a path for third-harmonic currents, preventing harmonic voltage distortion.
The 30┬░ phase shift is a standard characteristic used for parallel operation compatibility.
Delta-Star is highly effective for unbalanced loads due to the neutral return path.
Provision of a stable neutral point for 3-phase, 4-wire systems.
Capability to handle unbalanced loads without significant phase voltage displacement.
Reduction of third harmonic voltages in the output due to circulation in the delta winding.
Introduction of a 30┬░ phase shift prevents direct parallel operation with ╬ФтИТ╬Ф or YтИТY transformers.
Higher insulation cost for the secondary winding if the neutral is not grounded.
Distribution transformers for residential and commercial supply.
Step-down applications where a neutral wire is required for single-phase distribution.
Option B is correct because the star connection allows for easy implementation of Earth Fault Protection (EFP).
Option C is correct because the closed delta loop allows third-harmonic magnetizing currents to circulate, cancelling their magnetic flux.
Option D is correct because the neutral wire provides a return path for unbalanced phase currents.
A is correct тАФ In delta-star type transformer, secondary voltage is NOT in phase with the primary voltages due to a inherent 30┬░ phase shift.
Always remember the vector group notation: for ╬ФтИТY, the clock position is either 1 or 11, indicating a 30┬░ shift (1├Ч30┬░ or 11├Ч30┬░). Never assume phase-in-phase unless it is a YтИТY or ╬ФтИТ╬Ф connection.
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