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THOBIAS MABUGO
Associate

Join Date: Sep 2010
Posts: 45

3-Phase Ind. Motor Protection, Circuit Breakers

09/18/2010 8:58 AM

1.Which factors have to be considered when selecting LV circuit breakers(CBs) for

a)Three phase induction motor(IM)

b) Other loads

2.Most of the CBs available in the shops are AC CBs,can also be used in DC loads?

If not,which factors have to be taken into account for DC CBs selection?

Best regard

By T.mabugo(Dar-Tanzania)
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kvsridhar
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Join Date: Sep 2009
Location: Temporarily at Ashburn, VA
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Good Answers: 164
#1

Re: 3-Phase Ind. Motor Protection, Circuit Breakers

09/18/2010 11:14 AM

1. For motors, you need a starter to switch it on and off. The MCCB should only do a protection function. Its overload characteristic should be such that it will not nuisance trip during normal start.

Similar consideration of inrush and steady-state performance will be needed for transformers, capacitors, almost any load.

Check out this link for motor protection, and go on from there for other applications of MCCBs.... The great protection debate

2 AC devices will have some inherent DC capability, but considerably reduced. Especially as the voltage goes >250V DC. There are special DC circuit breakers designed with large open gaps, blowout coils, deion grids, so on.

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THOBIAS MABUGO
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Join Date: Sep 2010
Posts: 45
#3
In reply to #1

Re: 3-Phase Ind. Motor Protection, Circuit Breakers

09/20/2010 7:53 AM

Thank you for you comment.Please can you clarify more for LV MCCB sizing?,especially on 3-phase IM protection?
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kvsridhar
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Location: Temporarily at Ashburn, VA
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#4
In reply to #3

Re: 3-Phase Ind. Motor Protection, Circuit Breakers

09/20/2010 8:38 AM

If you are in USA or a country following US standards, that thread from Hameedullah (which shamithgambhir has quoted) is excellent.

If you are following IEC, please look at any Type 2 co-ordination table, here is one from ABB : abb

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SHAMITHGAMBHIR1
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India - Member - design engineer Engineering Fields - Electrical Engineering - New Member United Arab Emirates - Member - New Member

Join Date: Feb 2010
Location: dubai,mangalore,bangalore.....
Posts: 145
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#2

Re: 3-Phase Ind. Motor Protection, Circuit Breakers

09/20/2010 7:43 AM

http://cr4.globalspec.com/thread/56416#comment586920

2) DC Breakers are available in most breaker brands ...factors for considering dc breakers r almost similar to AC like OverCurrent, SC current etc........

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Previous in Forum: Hello Dear, I Want Understand Transformer Tan Delta Test   Next in Forum: How Many mmsq Aluminium 4 Core for 60 KVA 3phase 400V 50 Hz

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