Problem Related to Earth Fault (Micom123)

This could be due to

• missing of one of the phases at the relay
• wiring a phase CT at the residual current signal input to the relay (wrong wiring)
• Polarity of one of the phase CTs is wrong resulting in high residual current to the relay

Is the primary injection of CTs and polarity check done during commissioning!

Many times, the actual connections in the panel differ from those shown in the panel drawings and it is important to take time and establish correct ratio, polarity and the wiring to the relay.

Since the relay is in buscoupler panel, presume the relay is measuring residual current and there is no neutral CT input coming to the relay (unlike the trafo neutral CT input to the incomer relay).

As suggested by raghun

Please check CT connections, and polarity.

maybe its a true earth fault, so current is flowing to ground [earth].

Well Mr.Capy, if its a genuine earth fault, I do not think the fault current increases in direct proportion to the load. There cannot be an earth fault in each and every equipment which is being switched on.

Micom Relays measure Earth Fault Current from the Zero Sequence Component of the phase current inputs. At the time of motor starting or a battery charger energising, there could be large zero sequence components in the input currents, due to the magnetising inrush current of the motor or the input transformer of the battery charger. Try increasing the time delay of the earthfault element.