Abstract: A method of and a device for monitoring poly-phase currents in poly-phase equipment, in which a phase signal representative of the current in each phase of the equipment is obtained, the phase signals multiplexed so as to obtain a single multiplexed signal, and the multiplexed signal then processed to extract from it an output signal or signals representative of, for example, overload, unbalance, earth fault or short circuit conditions.

Abstract: 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.