87T- Transformer Differential Protection Overview

87TAPRICT_87T takes in the settings of transformer differential protection settings from the  entered by the user. The TAP settings are immediately calculated. These TAP settings are the correction factors that convert the currents on both sides of the transformers from primary quantities to per unit (PU) values. The calculator further calculate the PU restraint currents which are used to derive the compensated operating current based on the slope settings. The tabled per unit restraint and operating currents give the restraint differential characteristic of the restraint differential protection.

With the restraint characteristic determined, APRICT_87T further calculates the secondary current test values for the locus of points on the restraint differential characteristic. 

Using the calculated test points, APRICT_87T calculates the secondary current values corresponds to each set of restraint and operating currents. The current injection to the values are the inputs currents on the high and low sides of the transformer  to the differential protection relay will create an unbalance current to  to operate the differential protection.

APRICT_87T also has the selections for the user to choose the which phase/s of currents and winding to be simulated from balanced condition to a fault condition. This feature guides the user to follow the sequence of test recommended by APRICT_87T.   (Click image to enlarge)

Try online to see how the settings change the protection characteristic..

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