MICOM P123 – Three-phase overcurrent and earth-fault protection


MICOM P123 devices are relays operating on the basis of digital technology. The module has 4 analog inputs, including 3 current inputs and 1 zero current input. These currents can be set to two ranges, 1A or 5A. The device allows any programming of output relays as a protection or control function, as well as programming of digital inputs. The relay can be powered from an AC or DC source with a maximum power interruption lasting 50 ms. The front panel of the device has information LEDs and function buttons. The internal memory stores system alerts, that are displayed on the LCD display. Information on alerts, parameters and measurements are available for viewing on the display and stored in memory without the need to enter an access password.


Fig. 1. Front panel of the MICOM P123 device family

The front panel keypad includes navigation buttons, a confirmation and selection button. It also has 8 LEDs, four of which are programmed in advance, and four can be freely programmed. Under the bottom cover there is a 9-pin RS232 port for local communication. The device is capable of measuring phase and zero currents, given as RMS values up to 10 harmonics at 50Hz. Remote data reading from the module’s memory is available via RS485 sockets with Modbus, Courier, IEC or DNP 3 protocols. There is also a modification and data processing via RS232 ports connected to a PC unit with built-in software for this purpose. Connection of the device can be realized via a communication network with the SCADA control system. During operation of the device, it is possible to remove relays from its housing. The current circuits are automatically shorted.

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