METHOD OF AND A PROTECTION RELAY FOR PROTECTING ELECTRICAL EQUIPMENT

A method of and a protection relay for protecting electrical equipment. The method includes dividing a predetermined dividend value by a signal corresponding to the load current in the equipment to provide a quotient signal, and then linearly integrating the quotient signal. When the integrated signal reaches a predetermined value, the equipment is tripped. This provides an overload vs tripping time characteristic which is substantially linear. The method further provides for sensing whether the equipment is operating in a start up mode or in a normal running mode, and then automatically to select a less sensitive overload vs tripping time characteristic when the equipment operates in the start up mode and automatically to switch to a more sensitive characteristic when the equipment reverts to its normal running mode.