PR Series:

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Protective current transformers are required to operate over a range of current many times the circuit rating and is frequently subjected to conditions greatly exceeding those which it would be subjected to as a measuring current transformer. When a current transformer is used to energize a protective relay, it must maintain its characteristic ratio up to some multiple of its rated current. This multiple, may be 5, 10, 20 or some even higher value and is know as the "Accuracy Limit Factor"(ALF). Therefore, the selection of Protective Current Transformers in relation to accuracy class and ALF require a close examination of relay characteristic and circuit conditions which includes the relay burden and the pilot wire lead burden.