The MK1000A combined overcurrent and earth-fault relay is
a microprocessor based numerical relay. It uses fundamental
frequency current measurement for excellent harmonic
current rejection. The relay provides three independent
phase overcurrent elements and one non-directional earthfault
element. All these elements are connected to the
current transformers of the feeder to be protected.
The overcurrent and the earth-fault elements consist of
independent low-set units and high-set units. The time
current characteristic of the low-set units are selectable
between inverse definite minimum time (IDMT) normal
inverse curve 3/10, normal inverse curve 1.3/10, long time
inverse curve, very inverse curve, extremely inverse curve
and definite time. The high-set units are the definite time
type, instantaneous tripping is made possible by setting the
time to minimum.
The MK1000A incorporates a 4-digit LED indicator which
allows direct numerical readout of set values, actual
measured value, recorded value and system indication. All
current measurements and current settings are based on 5A
current transformer (CT).