Under Voltage Relay/Release
What is Under Voltage Relay ?
An under voltage release is an optional device installed in a circuit breaker that automatically triggers a power trip when the power falls below a preset level, usually between 70 and 35 percent of the UV rating.
The circuit breaker does not power it. Instead, it receives its power from an alternative source, such as a battery. It was initially designed for use in coal mines but can now be found in any field employing heavy industry.
How it works
An under voltage release device consists of a solenoid magnet with a moving armature fixed to a spring-loaded latch. This latch restrains a spring-biased plunger, which when released, makes contact with the breaker trip bar to trip the breaker.
As long as the voltage connected to the solenoid magnet remains normal, the magnetic force is strong enough to overcome the spring force and keep the trip bar from releasing. But once the voltage cuts off or falls too far below the preset level, the spring force overcomes the magnetic force. This force unlatches the plunger, which then trips the power.
When the circuit breaker contacts are open, a mechanical reset leaver, powered by a central contact arm, holds the solenoid magnet in a sealed-in position. Once power is restored, the magnet reenergizes and holds the plunger in its position allowing the circuit breaker to be reset and turned back on. If the power has not been restored to the solenoid coil and someone tries to reset the breaker, it will only trip again.
Why do we use under voltage relays?
AC power needs to be in an acceptable voltage range. Under voltage , for example less than 90VAC and 0 might create damage in some devices. They are not designed for this “grey” area of input. For example compressors on air conditioners can draw excessive current when the voltage is low. An under voltage relay cuts off the AC until its in the correct range.
