Protection device and controller of three-phase asynchronous motors – MICOM P211

MiCOM P211 relay is an integrated device used for protection and control of three-phase motors. P211 allows efficient and selective motor protection and can be used with variously loaded motors, acting as independent protection/controller or as a relay integrated in a larger system. Thanks the implemented Modbus protocol is possible to communicate with the master system and exchange of information about the current status of the relay and measurements, as well as the control of the engine from the system level.

Relay MICOM P211


The motor protection modes offered by P211 are based on the measurement of phase currents and short-circuit current and each of the protections is individually configured. During tripping the relay registers the measured values of chase currents and current ground, and at start-up, the maximum starting current and the duration of the start-up.

The MICOM P211 relay is able to protect the motor against:

  • Effects of overloads (I>) – protection against overheating of the motor in dynamic states, based on mathematics thermal model of the motor heating condition calculated in real time on the basis of size effective phase currents. The parameters are the ratek current of motor Ib and the permissible time current flow equal to six times the rated current T6xIb.
  • Working motor under underloaded state (I<) – the relay allows detection of the fault condition or improper operation of the drive. Criterion protection is provided by undercurrent protection with a programmable delay time. The settings are: current threshold I< delay time.
  • Working with asymmetry of phase currents – protection against motor warm up when phase current asymmetry is based on control percent current asymmetry in subsequent phases. The setting parameters are: permissible asymmetry value and delay time of operation.
  • Phase loss – current drop below 0.1 x Ib in any of the phases is recognized as phase loss testifying to machines, connections or power supply, and the protection operates after a set time delay. Parameters are the rated current of the motor Ib and the response delay time.
  • Excessive engine temperature (PTC) – for motors equipped with PTC sensors, the relay allows you to control its temperature and protection against free temperature changes taking into account ambient temperature and conditions cooling. Resistance increase is treated by the relay as PTC sensors.
  • Ground faults (I0>) – ground current can be small, undetectable by overcurrent protection, so protection realized thanks to the external zero-sequence current measurement. Parameters is the setting threshold I0> and the delay time.
  • Short circuit (I >>) – such protection can be implemented for systems in which the control switch is a circuit breaker, able to disconnect short-circuit currents, it can not be used in contactor systems (short-circuit protection due to additional fuses). The parameters are the threshold of the current activation I >> and the time of crossing the threshold.
  • Extended start/locked rotor – when entering the starting current threshold lower than the starting current and the delay time above the start-up time and the delay time when the engine is running, P211 provides protection before extended start-up or blocked rotor.

If you want to expand more your knowledge here is the Laboratory test of Protection Methods of three-phase motors with the use of the MICOM P211 relay.


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