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The earthing transformer is used to
To avoid harmonics in the transformer
Provide artificial neutral earthing where neutral point is not accessible
Improve stability of the system
Measure the voltage
Provide artificial neutral earthing where neutral point is not accessible
An earthing transformer (or grounding transformer) is a specialized transformer used to create a neutral point in an ungrounded or delta-connected power system. It provides a path for zero-sequence currents, enabling the detection and isolation of ground faults in systems where no physical neutral exists.
An earthing transformer (or grounding transformer) is a specialized transformer used to create a neutral point in an ungrounded or delta-connected power system. It provides a path for zero-sequence currents, enabling the detection and isolation of ground faults in systems where no physical neutral exists.
I0тАЛ=31тАЛ(IAтАЛ+IBтАЛ+ICтАЛ) тАФ Definition of zero-sequence current component in fault analysis
ZgтАЛ=IfaultтАЛVLNтАЛтАЛ тАФ Grounding impedance provided by the transformer
The device typically employs a zig-zag (interconnected star) winding configuration. Under normal balanced conditions, the zero-sequence currents are negligible. During a ground fault, the zero-sequence current flows through the zig-zag windings in a way that the magnetic fluxes cancel out in the limbs, offering a low-impedance path to the ground while maintaining system stability.
Used in delta-connected systems where no access to the neutral point exists.
Commonly utilizes the 'Zig-Zag' connection to minimize zero-sequence impedance.
Allows for the installation of neutral grounding resistors or reactors.
Must be rated for the duration of the ground fault current.
Provides a stable neutral for systems without one.
Limits transient overvoltages during ground faults.
Allows sensitive earth fault protection relaying.
Additional capital cost.
Requires space in the substation.
Contributes to total system fault current.
Industrial delta-connected distribution networks.
Mining and heavy manufacturing power grids.
Systems requiring high reliability for ground fault monitoring.
A zig-zag transformer has no secondary winding; it is a single-winding transformer designed to pass fault current.
Option A is incorrect because harmonics are typically mitigated by filter banks or specific winding configurations in power transformers, not earthing transformers. Option C is incorrect as earthing transformers often increase fault levels slightly, potentially reducing short-term stability.
Option D is incorrect as voltage measurement is the primary role of Potential Transformers (PTs).
B is correct тАФ An earthing transformer creates an artificial neutral point in a delta-connected system, allowing for ground fault protection and limiting system overvoltages.
Always remember that an earthing transformer carries current only during a ground fault condition; it is sized based on the fault current duration and magnitude rather than continuous load capacity.