when “VA” of a protective current transformer connected with a protection relay is properly sized , it is guaranteed that the current injected to the relay does not exceed e. g. 20 times of the relay rated current . But , when this CT is replaced by a more expensive CT of higher burden , it is not guaranteed that the current injected to the relay is 20 times . it is higher than 20 times and will damage the relay .(In fact it goes to saturation region later and higher secondary current is generated)