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    How to Test a 3 Phase Monitoring Relay?

    A monitoring relay is a commonly used electromagnetic relay that is used for the voltage protection and control of the power drag system. The coil is connected to the main circuit in parallel to sense the line voltage of the main circuit; the contact is connected to the control circuit and is the executive element. According to the size of the pull-in voltage, voltage monitoring relays can be divided into over-voltage relays and under-voltage relays. ATO monitoring relay has a great many function, including overvoltage protection, undervoltage protection, voltage unbalance protection, phase failure protection and wrong phase protection.

    This is a 3 phase multifunction monitoring relay. It has LCD display, nameplate and circuit diagram on the side.

    Multifunctional monitoring relay

    We test according to its circuit diagram connection. And the load is a three phase motor.

    Multifunctional monitoring relay wiring diagram


    Enter parameter in monitoring relay

    Long press "MOD" to enter the parameter setting interface.
    "RST" is the exit key.
    Enter "MOD" and press + or-to modify the value.
    Short press "MOD" to display the working times, working time, fault times and fault time.
    Press + or-to display AB, BC, AC voltage (line voltage).

    Note: For the meaning of the parameters, please refer to the instruction manual.

    Phase loss test

    Phase loss test of monitoring relay

    When one of the phases is disconnected, the LCD displays a phase loss, the contactor fails to close, and the motor stops. This avoids damage to the motor.
    We resume the phase, the LCD shows that the voltage is normal.
    When "RST" is pressed, the contactor is re-engaged and the motor runs again. (Manual or automatic reset can be adjusted in the parameter settings.)

    Test wrong phase protection function

    Monitoring relay voltage display is normal

    Change the position of L2 and L3. At this time the order is L1, L3, L2.
    Power on, the monitoring relay voltage display is normal.
    We noticed that the LCD displays "SEQ", indicating the wrong phase.
    The contactor cannot be closed normally, so as to achieve the purpose of protecting the motor.

    View the video below to know more about ATO 3 phase monitoring relay phase failure & sequence test.

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