FIELD: electrical engineering. SUBSTANCE: device is intended for automatic switching-on of stand-by power supply of users with synchronous motors. With emergence of asymmetric short-circuits in supply line due to asymmetry of interphase voltages responding element operates depending on signals across outputs of miniselector and maxiselector. Settings of these selectors for minimal relative operation voltages for unbalanced and balanced drops of voltages of main source are monitored by voltage dividers. EFFECT: enhanced sensitivity and speed of response for automatic switching-on of stand-by power supply. 2 dwg
