Oil immersed Earthing Transformer

The oil immersed earthing transformer

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The oil immersed earthing transformer  is used for providing a manually loadable neutral point for the non-earthed point in the power system, this neutral point can be connected to the arc suppression coil, earthing current limited reactor or resistor, it can be connected to the earth directly as well.

 The primary side neutral point of earthing transformer can be used of earthing, the secondary winding can be connected to a continuous load which is used for the auxiliary power supply of the substation.

Why are grounding transformers needed?
Simply put, a grounding transformer is used to provide a ground path to either an ungrounded wye or a delta-connected system. Grounding transformers are typically used to:
Provide a relatively low-impedance path to ground, thereby maintaining the system neutral at or near ground potential.
Limit the magnitude of transient overvoltages when restriking ground faults occur.
Provide a source of ground fault current during line-to-ground faults.
Permit the connection of phase-to-neutral loads when desired.
If a single line-to-ground fault occurs on an ungrounded or isolated system, no return path exists for the fault current, so no current flows. The system will continue to operate, but the other two un-faulted lines will rise in voltage by the square root of three, resulting in overstressing of the transformer insulation and other associated components on the system by 173%. Metal-oxide varistors (MOVs), solid-state devices used to suppress voltage surges/spikes (lightning arresters), are particularly susceptible to damage from heating by leakage across the blocks, even if the voltage increase is not sufficient to flash over. A grounding transformer provides a ground path to prevent this.
Grounding transformers are normally constructed with one of two configurations: a zig-zag (Zn)-connected winding (with or without an auxiliary winding) or a wye (Ynd)-connected winding (with a delta-connected secondary that may or may not be used to supply auxiliary power). Both arrangements .The current trend in wind farm designs is toward the wye-connected primary with a delta secondary. Based on our experience, there are several reasons why the 2-winding wye-connected grounding transformers are seemingly more popular than zig-zag designs

The oil immersed earthing transformer for the three-phase transformer (or three-phase reactor)  is used for providing a manually loadable neutral point for the non-earthed point in the power system