High Z vs Low Z diff protection?
High Z vs Low Z diff protection?
(OP)
Hi
I am wondering if someone could tell me exactly just what is meant by high Z differential protection (e.g. restricted earthfault) and what is meant by low impedance diff protection, e.g. biased differential. What does the high and low refer to?
Thanks.
I am wondering if someone could tell me exactly just what is meant by high Z differential protection (e.g. restricted earthfault) and what is meant by low impedance diff protection, e.g. biased differential. What does the high and low refer to?
Thanks.






RE: High Z vs Low Z diff protection?
Most of the major relay manufacturers have good descriptions in the tech literature on their websites.
Bung
Life is non-linear...
RE: High Z vs Low Z diff protection?
High impedance systems - voltage operated
Low impedance systems (bias or unbias) - current operated
Main disadvantage of circulating current protection using low impedance relays is through fault instability due to CT saturation.
Main disadvantage of high-impedance protection is the need for dedicated CTs.
The trend in modern relays today is to go with low impedance schemes.
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RE: High Z vs Low Z diff protection?
With the advent of microprocessor relays, there is a renewed interest in using low impedance differential protection, similar to generator differentials and transformer differentials. This requires a separate CT input to the relay for each CT.