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CT Selection for Restricted Earth Fault protection

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babambu

babambu

Electrical
Joined
Mar 18, 2002
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5
Location
ZA
The 6.6kV Star side of an 7.5MVA transformer is earthed through current limiting resistor to 300mA. The CT on the earthed side are 1250/1A. The phase CT on the Transformer are 800/1A. Will the mismatch on the CT ( 1250 and 800) be a problem? If not a problem how are these CT connected including the relay to show zero amps. If yes there is a problem, how can I solve it
 
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Babambu,
It is not an issue if you are using a low impedence protection for REF.
 
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normally numeric relays have large setting ranges. Siemens relay can matching 5A-CT secondary with 1A-CT secondary
 
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