This course deals with transformer differential protection, analyzing schemes, various relay settings and protection testing. We will analyze the transformer differential schematics and talk about current transformers (CTs), CT errors and errors due to the tap changer in the transformers.
Special attention is paid to biased differential protection of transformer and modification of standard scheme by providing a restraining winding which is energized by the through current. We will also discuss relay protection setting calculations, MS Excel calculation sheet & plotting of slope, relay characteristics and trip characteristics.
The last lessons are dedicated to drawing the relay settings calculations curve and finding a point of intersection and drawing protection characteristics.
Power Transformers generally develop rare faults as it is static, totally enclosed and oil-immersed but if these faults sustain the results may be serious unless the transformer is disconnected.
The best way of protecting power transformers against an internal fault is by the method of differential protection scheme since it covers the transformer’ zone of protection. So for a transformer having ratings of 5 MVA and above, the differential scheme serves as an important protection against internal phase-to-phase and phase-to-earth faults.
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