CT for restricted earth fault (REF) protection

AI Thread Summary
For Restricted Earth Fault (REF) protection, the nominal primary current transformer (CT) ratios typically need to be the same in high impedance systems, while low impedance systems allow for different ratios. The current transformers in use include a 2000/5 CT on the 20kV switchgear and a 1200/5 CT on the neutral of the power transformer. The Areva Micom P632 relay is recommended for this application. Additionally, resources such as Protection Riddle No.59 can provide further insights into low and high differential protection. A request for a three-line diagram of a 500kV substation was also made by a participant seeking guidance on the topic.
saragiha
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Does somebody could advice me, whether the nominal primary CT to be used for REF protection must be same?

The CT I have now as follow:
Power Transformer: 60MVA, 150/20kV, Ynyn(0)d1
CT on 20kV switchgear 2000/5, class 5P20
CT on neutral Power Transformer: 1200/5, class X
Relay to be used: Areva Micom P632
 
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Generally in high impedance Restricted Earth Fault (REF) protection, the ratio of involved CTs must be same, but in low impedance type it can be difference.
For more information about low and high differential protection also REF you can refer to Protection Riddle No.59 and other riddles from http://electrical-riddles.com
 
Dear msj,

thank you, helpfully
 
three line diagram of 500kV Substation

Hi...

Does somobody have a sample three line diagram of 500kV Substation?
I will have a disscussion of this topic, unfortunately I'm new on this topic.

Regards,
Saragiha
 

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