CT for restricted earth fault (REF) protection

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
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


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.


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