The digital protection relay for 550 kW - 1 MW asynchronous motors is investigated in this finishing work. In the theoretical chapter are examinated the structure of multifunctional protection relay, non-regular asynchronous motor operating conditions and their reasons. Two operating conditions are marked out, first - when supply current is changed, second - alternation in supply voltage. Next is made investigation of Siprotec 7SJ621 digital protection relay. There's made survey of 630 kW power asynchronous motor from non-regular operating konditions when there was overcurrent and overvoltage in the supply.