Air Circuit Breaker

If there is no undervoltage release, the ACB will stay ON when power goes off. When power comes on again, all loads will get the supply. Quite often (though not always), this may cause some dangerous situations in the connected load eg. some machinery starting suddenly. To avoid this, u/v releases are used in ACBs. IEC 60947-2 specifies how a u/v should work. Does not make it mandatory.

What is the dangerous situation in the connected load, when all loads gets the supply?.....All machineries are directly connected to ACB??...No control panels or starters?.....

If you don't have any problem, you need not use any UV releases. No issue.

So whatever you already said in this forum are all useless??.......

As krsridhar said restoring power to a system with a closed ACB could cause problems.

Alternatively you could have a critical application where power loss would cause problems. An emergency generator automatically starts up due to a mains failure. It restores power to the system but your ACB has opened due to UV, time is lost while you close the ACB.

Each situation needs to be assessed on it's requirements.

Following our guests reply to krsridhar, I wish I hadn't posted the above reply.

Dear guest, please find another forum, as far as I'm concerned your not welcome here!

I second you TonyS. Ksridhar is a well respected member on this forum whose opinions are taken with all the due respect they deserve.

BBRaina

Dear BB Raina,

Thank you very much for your kind words, i will try to live up to them...

UV protection is not only for these reasons. what kvssridhar said is wrong,but may be he wish to communicate something else. What is your problem if guest has asked that to kvs?....

i am intrigued. Can you please explain where i have gone wrong ? i am asking you not in anger or as a challenge, but with a genuine interest in learning.

Perhaps other CR4 experts can also comment ?

Main reason is protection of motors in many equipments being under voltage which will create high current draw from the line and related consequences. This is not given in your post. As per IEC undervoltage protection is mandatory.

Most of or all equipments has MCC panels and control panels , which already fitted with under voltage protection too. Even in small distribution boards, feeding lighting and power, we have under voltage and phase failure relay for A/C machines. say window a/c or split units. Hence it is wrong to say that UV in the main ACB is to protect from starting machines together.

I suggest you to read IEC standards regarding the voltage range, deviation, motor safety factor etc. ...Today I dont have time. I will explain you tomorrow with the details from IEC standards.

i look forward to further information from you. i have gone through 60947-1 and 2, and could not find any clause that makes it mandatory to have a UVR on ACB/MCCB.

i have worked with three companies who made ACBs, and the sales of UVRs, sold as accessories, sometimes factory-fitted, sometimes sold loose, was only between 20-35% of the total ACBs sold.Would have been 100% if it was mandatory.

One major application of the UVR is as an interlock between two ACBs, when, at best,only one ACB must be ON at any time. Being a "Fail-safe" device, it serves an excellent interlocking function to prevent two sources coming on to the system at the same time.

GA

I can also say: For a Main ACB (I presume it is a main input CB to be Air operated), to have a UV release coil is not a requirement because it will be a disruptive factor and will create more harm than benefit.

If safety or protection is the criteria, the UV coil could be installed down stream, near where there is a need to protect against unexpected running after a power cut or if the voltage drop is detrimental to the equipment.

KVSRIDHAR is correct ....

Guest: we are waiting for your quote from the standars requirement and I hope it will be clear and not a general vague statement.

According to IEC 60038 the voltage 230/400 v is +/- 10% . All equipments and motors to designed ,manufactured and tested accordingly. Hence UV protection,phase unbalance and over voltage protections are setted in this way. What did you said about 70 and 35% of the rated voltage is not understanding. In which country or standard it is allowed?... You are not wrong completely but it misguide by incomplete nature of answer.

My friend, we are talking here about (a) ACB and (b) UVR of ACB. IEC 60947-1 &2 as i have mentioned before. UVR is NOT mandatory. But desirable as others have said.

Which country ? My identity is visible. All IEC countries in fact. Here is an image from IEC 60947-1.

My best friend, first of all, you have to understand that every standard does not stay alone. You misinterpreted the content of IEC standard or purposfully trying to save your stand or just cheating others.

I suggest you to read the next two sentences of the image you posted here. May be other members will understand it properly.

This clearly stated about the operating voltage of UV relay and not the system voltage. It means UV relays shall capable work at 35% of its rated voltage.

And last, I do not think that any of IEC countries are allowing the voltage fall up to 35%.

This post is about ACB and an Undervoltage release which is an accessory of it. i have addressed that one only. The discussion has gone way beyond that. i am hurt by implications of cheating and other innuendos...but then you are entitled to your opinion, however wrong. Bye.

Installing uv tripping for motor feeders (breakers or latched contactors) is most often desirable.otherwise .1)All motors staring on restoration will trip the in comer if set for oc or uv protection.2)someone present near the motor or its driven equipment will get a shock.this need only be a release.

on essential equipment such as start up dg or a barring motor or invertror ckt uv as well as other lighter faults will set up only an alarm.

For lighting and essential circuits uv tripping is rarely provided. If provided they are generally to initiate changing over to an independent stand by source. ditto for un balance tripping. we would not want to be present in a place where a transient creates an avoidable uv black out. we cant expect customer to relish the same.

to be accurate motor has many uv settings-during starting to ensure adequate acceleration torque. otherwise no point in attempting a start it will stall.

during running as an alarm for impending over load trip for constant output loads.As well as a trip stage for some type of loads .but these are proper relays with accurate settings.

these are not applicable for loads like fans which can not be overloaded by slight uv.i am trying to high light a few aspects so better to check each instance rather than just follow standard and uv black out a good gathering for no reason except to satisfy the standard

proper interpretation and implementation of standards rarely gives a wrong result.

As Kvsridhar has said, you would not normally use something as crude as an undervoltage release to protect a motor against the effects of out-of-spec voltages. Undervoltage releases are usually on-off devices without the adjustment that would be needed to set the lower (and usually upper) voltage limits at which it should break the supply to the motor.

I guess it all depends where in the world you are as to what rules apply, but in my experience, if it was desired to protect a motor against out-of-spec voltages, one would use a proper motor protection relay, probably in conjunction with either a shunt release or UVR fitted to the breaker.

dear all , first of all this ACB is a main c.b in MCC panel [we have 6 each gen.set run synch.with each other and connected to bus bar vairy ACB ] so the desiner make it's design to just active open release coil in case of upnormal case and not installed UV release coil at all so the quation is According to the IEC 60947-2 What is the important of Uv in this case? and what is the standard control circuit to activate it?

If someone have acopy of this standard pls pase to me.

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