<p style="text-align:justify"><span style="font-size:14px">If the circuit breaker is switched ON when the fault is already existing, this facility can be used. If such a situation occurs, the numerical relay will issue a trip command instantaneously bypassing all delays. This feature is useful in two important applications.</span></p>

<p style="text-align:justify">&nbsp;</p>

<p style="text-align:justify">&nbsp;</p>

<ul>
	<li style="text-align:justify">
	<p><span style="font-size:14px">In directional overcurrent relay, we have seen that if the breaker is inadvertently made ON when the earthing switch is ON (0.2 % probability), the directional overcurrent relay fails to operate even though the fault is in operative direction. This is because all line and phase voltages are zero at the relaying point and hence torque developed by the relay is zero. This SOTF facility, in this case, will sense the fault and will issue a trip command instantaneously.</span></p>
	</li>
	<li style="text-align:justify">
	<p><span style="font-size:14px">If the breaker is switched ON when the earthing switch at the other end of the line is ON (there is no interlock between the breaker at one end of the line and an earthing switch at the other end of the line) by mistake, this is closing on to fault. As the fault is at the end of the line, the in-built instantaneous unit of the overcurrent relay cannot operate (as it is set for a triple line fault at 80 % length of the line). The time delayed unit will sense this fault and hence fault will be cleared after the set time delay. This was the case when conventional relays were used. But, with this SOTF facility in numerical relays, this situation is sensed as closing on to fault and hence the relay will issue an instantaneous trip command.</span></p>
	</li>
</ul>