For the operation of the Undervoltage release, the IEC states as per below
Test for limits of operation
Starting with the circuit-breaker open, at the temperature of the test room, and with the supply voltage at 30 % rated maximum control supply voltage, it shall be verified that the circuit-breaker cannot be closed by the operation of the actuator.
When the supply voltage is raised to 85 % of the minimum control supply voltage, it shall be verified that the circuit breaker can be closed by the operation of the actuator.
In the case of a release with a range of rated control supply voltage, this test is made at both the minimum and maximum rated control supply voltages.
So , the MN release has a supply range of 200... 250 V AC.
So operating threshold for closing is , 0.85 * 200 = 170 V ( minimum supply 200V as per range 200...250 V AC)
The under voltage coil shall permit closing of the equipment at supply voltages equal to or above 85 % of its rated value.
The U/V will open at 35% to 70% drop of voltage. and will pick to close at 85% of the nominal voltage (Un).
Please note that when the circuit breaker is closed and voltage drops down to say 50% of the Un. This will give command to U/V to actually open and thereby tripping the circuit breaker. On the contrary it will not allow the breaker to close when the supply voltage does not reach 85% Un.
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