The phase monitor supervises a three-phase or single-phase network: overvoltage and undervoltage, voltage window, phase failure, asymmetry, broken neutral and phase sequence. It is supplied from the monitored phases, so it needs no separate auxiliary voltage and no additional wiring; the monitoring function is selected with a single rotary switch, without a menu. The relay works with and without a neutral conductor, and the adjustable reset hysteresis and switching delay prevent a response to short disturbances.
DOLD names as benefits the correct direction of rotation of motors and pumps, protection of motors and plants on phase failure, high repeat accuracy and a wide measuring voltage range. The RN 9877 version covers networks with line voltages up to 525 V, the smaller RL 9877 networks up to 230 V.
For railways we propose it for monitoring the three-phase supply of trackside cabinets, substation auxiliaries and drives in technical rooms, and at point machines with three-phase motors for checking the phase sequence before switching on. The output operates in closed-circuit mode: loss of supply to the relay gives the same signal as a network fault.
Parameters (RN 9877.11/61, from the datasheet):
