FIELD: relay protection of electric motors under abnormal operating conditions. SUBSTANCE: protective gear has START button that functions to mechanically actuate power contacts of magnetic starter. One lead of magnetic-starter coil, in its turn, is connected through break contact of STOP button to common point of series-connected capacitor and resistor. Other lead of magnetic-starter coil is connected to motor neutral. Non-common lead of capacitor is connected to lagging phase and that of resistor, to leading phase of supply mains. Under normal operating conditions voltage across magnetic-starter coil is high enough to hold armature in attracted position. Upon occurrence of phase failure or considerable unbalance voltage across coil drops to value insufficient to hold magnetic-starter armature in attracted position with the result that starter contacts open and motor is disconnected from supply mains. EFFECT: simplified design of protective gear. 1 dwg
