Answer Posted / alan jenkins
Traditionally protection CT's were 5A output and a high vA because they had to drive electro mechanical protection relays which had a high burden, However with modern Digital and Numerical Protection relays the operating burden is very small hence the CT's dont have to be as big as they used to be. Also on modern distribution networks, fault currents can be very high and 5A CT secondary currents were also equally high.
much favoured on new and refurbished equipment is 1A CT's.
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