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satishhar
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Location: Karnataka, India
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Breaker and Fuse Question

10/31/2011 6:40 AM

What is the minimum operating time of breaker and fuse?

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JohnDG
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#1

Re: Electrical

10/31/2011 6:59 AM

You might as well ask "how long is a piece of string?".

The answer will depend mainly on the type of breaker or fuse, and the current. Could be anything from milliseconds to minutes (or maybe microseconds to hours).

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JRaef
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#4
In reply to #1

Re: Electrical

10/31/2011 10:38 AM

Just how long IS a piece of string anyway? And if it was rope, would it be longer or shorter? Does the material make a difference, i.e. is cotton going to require it to be longer than nylon? Inquiring minds want to know!

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JohnDG
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#6
In reply to #4

Re: Electrical

10/31/2011 10:55 AM
  1. Yes
  2. 42
  3. Three times a week.

Next question.

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hithuanand
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#2

Re: Electrical

10/31/2011 7:56 AM

Ideal time of operation (making or breaking a circuit) t = 0 Seconds.
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kvsridhar
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#3
In reply to #2

Re: Electrical

10/31/2011 8:10 AM

Well actually, not. 0 time will make the di/dt too high for the system to withstand. Arcing is actually a help in breaking a circuit.

That said, the quick and efficient quenching of the arc is what designers are striving to improve every day.

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hithuanand
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#5
In reply to #3

Re: Electrical

10/31/2011 10:38 AM

Thank you Now i remember RRRV,opening circuit when sinusoide reach 0 current,increasing arc resistance etc. and other methods of arc quenching. I thought CB operating time is 0 seconds as an ideal switch.
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wareagle
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#7

Re: Breaker and Fuse Question

10/31/2011 11:43 AM

Quote "Just how long IS a piece of string anyway? And if it was rope, would it be longer or shorter? Does the material make a difference, i.e. is cotton going to require it to be longer than nylon? Inquiring minds want to know!"

Damn you JR. Now I will be up all night trying to figure this out.
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electricalexpert65
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#8

Re: Breaker and Fuse Question

10/31/2011 8:39 PM

What breaker? EHV or HV or MV or LV ? What type? Oil or Air or Vacuum or SF6? What opertaing mechanism? Spring assited or Pneumatic or Hydraulic?

What Fuse? Rewirable or HRC?

There are n number of questions that arise in my mind before answering your question. Please be more specific.
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sriram1988
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#9

Re: Breaker and Fuse Question

11/01/2011 5:27 AM

Fuse is one of the fast acting protection device .Its operating time of 0.4 microseconds.

Breaker operation time depends on 'Breaker settings'.
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kvsridhar
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#10
In reply to #9

Re: Breaker and Fuse Question

11/01/2011 7:23 AM

Agreed that fuses are very fast, but 0.4 μs is too fast. Where did you get that figure ? The time for fuses to clear the highest fault levels is a few milliseconds. Please get some insight into fuses by going through this booklet http://www1.cooperbussmann.com/pdf/092bf8cb-767c-4bac-8b87-8e0838fc3585.pdf

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sriram1988
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#11

Re: Breaker and Fuse Question

11/01/2011 10:42 PM

I agree with you Mr.sridhar ,fuse may take few Milliseconds to operate to highest of fault.As per my little knowledge

For High Fault Level:

Fuse operates faster than the Breaker.

above statement is wrong?

plz comment on it ...
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electricalexpert65
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#12
In reply to #11

Re: Breaker and Fuse Question

11/01/2011 11:25 PM

"For High Fault Level:

Fuse operates faster than the Breaker"

Dear Mr. Sriram, you have quoted the above statement from my answer to one of your other postings. You could have asked me for clarifications. Well! Let me explain:

HRC Fuses follow an Inverse Time-Current Charecteristics. So, at low fault currents their operating time would be higher. But, beyond about 20 times the rated current of the HRC Fuse, it operates in under 4 milli-seconds (approximately).

Whereas, breakers, particularly today's MCCBs, have a feature called "current limiting" and hence they open in under 10 mili-second approximately, due to a principle called "repulsion principle". Evenb non-current limiting type MCCBs, have an instantaneous release and if the fault current is more than the setting made in the instantaneous release, the MCCB opens in about 20 milli-seconds, irrespective of whether the fault is a low level fault or a high level fault. And, this instantaneous current setting may be set to anywhere between 2 to 16 times the rated current of the MCCB.

In case of ACBs too, though they do not have a "current limiting by repulsion" feature, they too have instantaneous releases in them wherein they can trip in about 25 to 40 milli-seconds, irrespective of the fault being low or high, as long as the current is more tahn the setting made in the inst. release. Here again, the inst. release setting can be anywhere between 2 to 16 times the rated current of the breaker or the CT Tap.

Hope it is clear.

I strongly recommend that you undergo a formal training on switchgear or at least learn to study the time-current curves of Fuses and Breaker Protection releases.
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kvsridhar
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#13
In reply to #11

Re: Breaker and Fuse Question

11/01/2011 11:51 PM

EE65 has adequately answered. i would like to mention here the innovations that are being done everyday to make current-limiting breakers even faster. This oscillogram of LS Susol MCCB is interesting i hope....

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electricalexpert65
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#14
In reply to #13

Re: Breaker and Fuse Question

11/02/2011 4:24 AM

KVS! Does it mean that the MCCB opens in 1.3 ms?
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kvsridhar
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#15
In reply to #14

Re: Breaker and Fuse Question

11/03/2011 9:32 PM

Yes. i was also skeptical at first, but then this test was done at KEMA, and the product is the clone of the famous Compact NS double-break rotary contact system of Schneider Electric. The NS clears the fault consistently in ≈2.5ms, and LS have improved it even more. Superb technology.

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electricalexpert65 (3); hithuanand (2); JohnDG (2); JRaef (1); kvsridhar (4); sriram1988 (2); wareagle (1)

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