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Ajay Patel
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Join Date: Apr 2009
Location: DR Congo
Posts: 31
Good Answers: 2

Neutral CT Specs

06/09/2009 6:52 AM

Can anybody help me for selection of Neutral CT specification for Star wound primary & Start wound seconday of Transformer.

Transformer rating id 40 MVA, 220 kV 11 kV. Means Primary rated current = 105 amps & Sec rated current = 2100 amps.

220 kV side & 11 kV Side neutral is Solidy Earthed.

I want to fix Neutral CT in both primary & Seconday neutral for REF (64) protection & Stand by Earht fault (51G, 50G) protection for Transformer.

I want to know what should be CT Ratios for both the type of protections & What is reason behind it?
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jack of all trades
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New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member Engineering Fields - Electrical Engineering - New Member

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Location: Auckland, New Zealand
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#1

Re: Neutral CT Specs

06/09/2009 3:38 PM

Have a look at previous threads on CR4 on this subject for the answers. To start you off, your CT ratio depends on what protection device the CT is being connected to. Look in the data sheets of said protection device(s) and it will tell you what the ratio of the secondary side of the CT needs to be.

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Anonymous Poster
#2

Re: Neutral CT Specs

06/10/2009 4:24 AM

hi

for that u need to first calculate earth fault current at primary and at secondary too.

and CT mustnot get saturated at that fault current, so accuracy class must be so pricise, which can withstand high fault current with keeping its secondary current with in limit,
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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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#3

Re: Neutral CT Specs

06/19/2023 6:06 AM

Surely a telephone discussion with the <...Transformer...> manufacturer is quicker than waiting for CR4?

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