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Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
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For a star-delta transformer with star-side grounded, the zero sequence current
Has no path to ground
Exists in the lines on the delta side
Exists in the lines on the Y side
Exists in the lines on both Y and delta sides
Exists in the lines on the Y side
In a star-delta transformer where the star side is grounded, the zero-sequence currents can flow in the lines of the star side because there is a physical path to the ground. These zero-sequence currents then induce circulating currents in the delta-connected secondary, but they do not appear as line currents on the delta side.
In a star-delta transformer where the star side is grounded, the zero-sequence currents can flow in the lines of the star side because there is a physical path to the ground. These zero-sequence currents then induce circulating currents in the delta-connected secondary, but they do not appear as line currents on the delta side.
I0(line)тАЛ=IaтАЛ+IbтАЛ+IcтАЛюАа=0 (For Star side)
I0(line)тАЛ=0 (For Delta side)
The zero-sequence impedance seen from the star side is finite because the ground connection provides a return path for the zero-sequence current (I0тАЛ). On the delta side, the zero-sequence component is trapped as a circulating current within the closed-loop windings, which prevents zero-sequence currents from exiting into the delta-side transmission lines.
Grounding on the star side provides a low-impedance path for zero-sequence current.
Zero-sequence currents in the star winding induce circulating currents in the delta winding.
The delta winding acts as a trap for zero-sequence currents, preventing them from appearing in the lines on the delta side.
The zero-sequence impedance of the transformer is determined by the connection type.
Provides a reference point for voltage grounding
Delta winding suppresses third-harmonic currents
Requires proper protection relaying for earth faults
Increases complexity in ground fault current analysis
Distribution transformers
Power transmission networks
If the star point were isolated, the zero-sequence impedance would be infinite, preventing zero-sequence current flow.
Option B is incorrect because delta connections inherently block zero-sequence current from entering external lines.
C is correct тАФ For a star-delta transformer with a grounded star point, the zero-sequence current has a return path through the ground on the star side, allowing it to exist in the star-side lines.
Always remember: A Delta connection acts as an open circuit for zero-sequence currents (from the perspective of external lines), while a grounded Star connection acts as a path.