The differential current relays type SKC is intended for the protection of generators, large motors, two winding power transformers and short lines.
The relay SKC feature the following characteristics:

• seven current inputs, where six are provided for current phase measurements and the last one dedicated for residual current measurement;
• internal compensation of phase shift and ratio matching for transformers differential function (87T); conventional external compensation can also be selected with external CT's;
• stabilizing circuit with dual slope with variable bias makes the differential functions of SKC relay insensitive to external fault (87T, 87G);
• second and fifth harmonic restraint stabilization with strong magnetizing inrush currents and overexitation condition (87T) based on numerical processing of differential current (DFT algorithm);
• alernative set thresholds for 49-50-51-50N-51N/87N protection functions which are automatically enabled upon detection of high second harmonic above a programmable set-point to prevent tripping for transformer energization (inrush);
• earth fault protection insensitive to thirth and higher harmonic components;
• selectable operation curves with independent or dependent time (first thresholds) for overcurrent and earth fault functions;
• trip counting performed for each function;
• shorting values of input quantities corresponding to the four last operations (START or TRIP) and trace memory with pre and post trigger;
• four final relays, independently programmable as energized/de-energized and latched/no-latched;
• three signalling LEDs (ON,TRIP,ALARM);
• two digital inputs circuits;
• double set-point groups (bank A and bank B)
• blocking circuits to perform accelerated protection schemes either with programmable logic from internal funtions with block circuits of external protection relays;
• trip circuit supervision (TCS)
• breaker failure protection (BF)
• serial communication circuit RS485 with MODBUS RTU protocol;
• real time clock with memory backup;
• continuous monitoring of internal circuits ;(SELF TEST).