<p style="text-align:justify"><span style="font-size:14px">The conventional relays were giving trip signal to a breaker. But, if the trip coil of the breaker is open or if there is some trouble with operating mechanism of the breaker or the air (or gas) pressure is insufficient to operate the breaker, the breaker will not trip and hence the fault will not be cleared. There was no facility in conventional relays to monitor the failure of the breaker. But, in numerical relays such circuit breaker failure function is available. Referring to figure 7.34(a), there is a fault at F. Relay R<sub>2</sub> senses the fault and operates as per its characteristic. R<sub>2</sub> gives signal to the breaker CB<sub>2</sub>. Now, if CB<sub>2</sub> fails to trip (because of any trouble of the breaker), R<sub>2</sub> will sense this failure of the breaker CB<sub>2</sub>, it will wait for some time (CB<sub>2</sub> operate time plus some safety margin) and after expiry of this (adjustable) time, the relay R<sub>2</sub> will generate another signal which can be used to sound an alarm (informing that CB<sub>2</sub> has failed) or the same signal can be used to trip the upstream breaker CB<sub>1</sub>.</span></p>

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<p style="text-align:justify"><span style="font-size:14px"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16292803141629280314.jpg" style="height:598px; width:800px" /></span></p>