Load Blinders in MiCOM Relays
Load blinders are provided for phase fault elements to prevent maloperation in the heavy load condition. The purpose is to configure a blinder envelope that surrounds the expected worst-case load limits, and to block tripping for any impedance measured within the blinder region. Only fault impedance that is outside the load area will be allowed to cause a trip. The phase overcurrent elements are settable independently of the load.
A facility is provided to allow the load blinder to be bypassed any time the measured voltage for the phase in question falls below an undervoltage setting.
It is possible to set the impedance and angle setting independently for the forward and reverse regions in the Z plane.
There are two modes of operation, the three-phase mode and the single-phase mode. The three-phase mode uses positive sequence impedance (Z1), and the single-phase mode uses the normal impedance (Z) of each phase. The three-phase mode uses I2> blocking in addition to under-voltage. When single-phase mode is selected, the overcurrent blocking will be phase segregated.
The load encroachment applies a characteristic as shown in the Load blinder and angle
