![]() Normally, the operating coil carries no current as the current are balanced on both the side of the power transformers. Working of Differential Protection System ![]() ![]() The operating coil is placed between the tapping point of the restraining coil and the star point of the current transformer secondary windings. Restraining coils controls the sensitive activity occurs on the system. The restraining coil is connected between the secondary winding of the current transformers. The neutral of the current transformer star connection and power transformer star connections are grounded. The CTs on the star connected side are delta-connected and those on delta-connected side are star-connected. The power transformer is star connected on one side and delta connected on the other side. Connection for Differential Protection for Transformer Such types of protection are generally used for transformers of rating exceeding 2 MVA. The protection for internal fault in such type of transformer is to be provided by using differential protection system.ĭifferential protection schemes are mainly used for protection against phase-to-phase fault and phase to earth faults.The differential protection used for power transformers is based on Merz-Prize circulating current principle. External fault is cleared by the relay system outside the transformer within the shortest possible time in order to avoid any danger to the transformer due to these faults. ![]() The fault occurs on the transformer is mainly divided into two type external faults and internal fault.
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