Undervoltage Coils

Hi there,

Undervoltage coils are used to trip your breaker in case of a mains failure. If you use the undervoltage coil - your breaker will be tripped when the main power returns.

To prevent spurious trips though (voltage fluctuations) you would use a dip proof inverter. This will hold the voltage in for an adjustable period of time (0.3 - 1.5s).

Regards,

Craig

when main power returns breaker will get ON automatically? if so, how?i m talking about u/v coil in control circuit & not about u/v relay.when u/v happen in control ckt breaker will get tripped by a plunger action,will that plunger action make it On when control power normalises?

No, as previously posted, the UV coil will TRIP the breaker. It will need to be reset after tripping. The UV coil is called an "Under Voltage Release", or UVR, not a re-closing motor. You can ALSO fit a re-closing motor onto larger breakers if that is important, but you will need some sort of logic to control that automatically. The UVR would have nothing to do with that part of the operation.

will the bkr be ON again on its own

No, the undervoltage trip function is providing a system protection function and as such the breaker will NOT automatically reset. The three main reasons you would trip a breaker out in an under voltage event would be loss of a single phase, excessive voltage sag on one or more phases or manual emergency system shutdown initiation. In all of these cases you would not want the breaker to automatically reset on its own (which could cause a potentially dangerous or damaging event downstream of the breaker in question).

Hi all,

The only thing that will automatically close by itself is an Auto-reclosure. Even when this is used - it will only try and close a certain amount of times and then stay tripped.

As stated over and over - undervoltage is there to trip the breaker. You will manually have to go and charge the breaker and switch it on yourself - or use an Auto-reclosure.

It is very dangerous for a breaker to just reset and re-energise itself as you would need to know what caused it to trip and that the fault is cleared etc etc etc.

In the case of Auto-reclosure, and its use here in SA, this is used on HV power distribution. The power company uses this to re-close the breaker automatically if it trips. They will only do this three times - if the breaker trips the third time in a row - they send someone to investigate as it could be a more serious fault (usually cable theft in SA).

Regards,

Craig

I some cases UVR coil is use to interlock two source of supply with one at a time so as to prevent the collision between the two source. e.g Main and Generator supply .

If main goes off it breaker will trip and when it's on again while the generator is on.

Hello friend,

Calling it an Under voltage coil is a MISNOMER. Of course the coil gets de enrgised sensing NO VOLTAGE as similar to that of a NO VOLT Coil in an Air break contactor. But the operating device is called UNDER VOLTAGE RELEASE. The de energisation of the coil releases a latch assembly which enables the tripping of the breaker.

To make the breaker ON you have to energise the CLOSING COIL.

Regards.

UV Ciol has an additional function on Switching-On; it blocks to switch-on if voltage is under a predefined level.

Have a good day.

As was stated before, this is a protective function. This prevents loads downstream of the tripped breaker from loading down the re-energized bus. The principle of this is to re-energize loads in an orderly manner. This is true if the main power supply of a bus is lost and the alternate power (Main Generator via Emergency Diesel or other power source) is now supplying but is has a lower KW rating (which is commonly the case). By having the breakers on this bus trip due to undervoltage prevents overloading of the alternate source of power immediately. Again, the principle is to bring back loads in an orderly manner.

I hope this clears up some confusion.