Often, it is the voltage, current and/or the temperature that are measured and monitored as the physical and/or the functional operating parameters. Monitoring relays are used in switchgear technology for monitoring current, single and 3-phase, level differences, time delays and other kind of operational safety functions in all kinds of technology installations. A range of standard voltages, current ratings, temperature windows and process signals can be monitored by the different available monitoring relays.
Monitoring relays are specifically used for residual current monitoring where systems are prone to residual currents caused by dust, etc. and the monitoring relay along with a summation current transformer (CT) displays the actual residual current and changes the switching state. Insulation monitoring relays superimposes a voltage between the ground and the isolated network also called a protection zone in cases where the isolation faults in ungrounded AC or DC systems need to be checked. Monitoring relays are also used for level monitoring in systems that require isolation from the mains, speed monitoring of liquid levels for overflow, dry run and leak protection, speed monitoring relays are used for evaluating speed of motors through the pulses received by sensors attached to the motor for monitoring overload, load shedding, etc., temperature monitoring for motor and system protection by evaluating if device is operating within the specific operating range and motor protection where monitoring relays are used to protect motor windings by monitoring and detecting the thermistor motors for high ambient temperatures, high switching frequencies, long start-up and braking procedures, etc.
