Drives and Controls Magazine

Smart motor protection relay has built-in PLC

21 April, 2009

WEG has developed a motor protection system in the form of a “smart relay” that can replace arrays of single-function protection relays. The SRW01 relay provides quick and easy detection of faults in motor control centres with networking capabilities. As well as improving safety, it is said to reduce the amount of motor control hardware and wiring needed, and to allow fast, precise identification and recording of system faults.

The modular relay can be operated as an overload relay, or as a direct-on-line, reversing or star-delta starter. There is also PLC mode, with the motor protection disabled, that allows the relay to be programmed to provide local automation.

Protection is built in for overloads, over-temperatures, phase losses, current imbalance between phases, over- and under-currents, locked rotors, earth faults, and out-of-range frequencies.

The relay can also monitor: the rms current for each phase, and the average current in Amps or as a percentage; motor frequency; the numbers of motor start-ups and activations per type of failure; motor and relay running hours; phase imbalance levels; and internal earth fault currents.

The device supports Devicenet, Modbus-RTU and Profibus DP communications (with other protocols supported via plug-in modules). The relay can be linked via a mini-USB port to a PC for setting, programming, controlling and data-logging operations.

An optional dedicated HMI can show the cause of any trip, as well as being used to set up, monitor and operate the relay.

The relay is suitable for motor currents from 0.25–840A by using the appropriate current transformer. The smallest versions, for currents up to 25A, are 45mm wide. The largest are 265mm wide.