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Anonymous Poster

ACB rating for power transformer

07/30/2010 12:29 PM

can somebody help me to determine the right ACB rating for protection of power tranformer with the following specifications;

3.2 MVA, 13,800 volt/400 volts. also is their a specific formula for the transformer protection. is the BS standard which is Ib is equal or more than In and In equal or more than Iz. Ib is design current and In CB rating and Iz is conductorm ampacity.

The load connected to transformer are motors with the size of 400 KW mostly Chiller and compressors.
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Anonymous Poster
#1

Re: ACB rating for power transformer

07/31/2010 8:31 PM

We use AIR CKT. BREAKER for connecting and disconnecting manually did you mean ABCB?
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Dalton
Associate

Join Date: Nov 2009
Posts: 42
#2
In reply to #1

Re: ACB rating for power transformer

08/01/2010 12:32 AM

Oh sorry. what i mean is VCB Vacuum Circuit Breaker for 3.2 MVA, 13800/400 volts transformer, 3 phase
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Simon Wan
Guru

Join Date: Apr 2007
Posts: 577
Good Answers: 10
#3

Re: ACB rating for power transformer

08/02/2010 12:44 AM

Which side do you want to protect your power transformer? The Primary Side or the Secondary side?

For your Secondary side of your power transformer, with the voltage of 400V, the total output capacity current from your power transformer will be about 4,618 Amps. So you need a ACB of 5,500 Amps or 6,500 amps with CT's ration of 5000/5 for overcurrent protection and earth faults protection.

For your primary side of your power transformer, that is the 13.8KV input, you will need a VCB rated at 630A/31.5KA with CT's ratio 150/5 as your total current for your power transformer is about 133 amps.

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PWSlack
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United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
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#4

Re: ACB rating for power transformer

08/02/2010 12:46 AM

.......and why can't the transformer manufacturer advise? After all, it does have a reputation to protect!

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