Under Voltage Relay

[Linspire]

Anyone mind to to share what's the function for under voltage relay to be installed in LVAC system ?

 

[Marmite]

On LV systems, probably to trip the controlling circuit breaker for loss of a phase.

Regards
Marmite

 

[DRWeig]

Marmite gave the reason that I use them most frequently, to prevent 3-phase motors from running single-phase, or attempting to start single-phase.

We also use them to simply detect low voltages that are not a lost-phase. Occasionally there is sensitive equipment to protect in this way.

Best to you,

Goober Dave

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[rcw retired EE]

Does the system have circuit breakers contolling motors? When power is lost, the circuit breakers will not trip open like a motor starter does. The motors will start when power returns. An UV relay trips the breaker unless power is available.

Is there a standby generator or another source of power on the system? The relay might be signaling for transfer to another source or be part of an interlocking scheme to prevent backfeeding.


Many possible uses.

 

[Linspire]

The designer actually design this UVR for MCCB which has timer close time which quite same as rcwilson said above.

As for DRWeigh's statement "to prevent 3-phase motors from running single-phase, or attempting to start single-phase"

From the control schematic, it only shows the source from 110 DC supply and there is motor integrated together. Does this mean it is single-phase motor of MCCB and there's 3 items for each control schematic design on each phases.

 

[DRWeig]

If the motor is 3-phase AC, one undervoltage relay monitors all three phases, and will trip on undervoltage in any phase. So it's a single input to your control system or a single dry contact in the coil control circuit.

Best to you,

Goober Dave

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