<p style="text-align:justify"><span style="font-size:14px">The relays discussed so far were measuring relays. There are other kinds of relays required for certain auxiliary functions.</span></p>

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

<ol>
	<li style="text-align:justify">
	<p><span style="font-size:14px"><strong>&nbsp;Tripping Relays:</strong></span></p>
	</li>
</ol>

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">We have discussed about these relays in basic tripping circuit.</span></p>

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

<ol start="2">
	<li style="text-align:justify">
	<p><span style="font-size:14px"><strong>&nbsp;Trip Circuit Supervision:</strong></span></p>
	</li>
</ol>

<p style="margin-left:48px; text-align:justify">&nbsp;</p>

<p style="text-align:justify"><span style="font-size:14px">We have seen in basic tripping circuit that a breaker trips on receipt of the signal given by a relay. A contact of protective relay energizes an auxiliary tripping relay the contact of which, in turn, completes the trip coil circuit. But if trip coil of the circuit breaker is open-circuited, the whole operation explained above will not be able to energize the trip coil of the breaker and the breaker will not trip. Hence a fault will not be cleared. Therefore, it is essential to check the integrity of a trip coil of any breaker at all times (24&nbsp;&times; 7)&nbsp;Checking or supervising the integrity of a trip coil is not only necessary when a breaker is closed (which is obviously understood as non-clearance of fault is hazardous) but also when a breaker is open. This is because the breakers have two separate coils: a closing coil and a tripping coil. Energization of closing coil results in closing the power contacts of a breaker and energization of tripping coil results in tripping of a breaker. Now when one is closing a breaker on fault (i.e., closing a breaker when a fault is already existing in an equipment to be protected) and a trip coil is not healthy, fault will not be cleared. Therefore, supervision of integrity (healthiness) of a trip coil of a breaker, irrespective of whether a breaker is open or closed, is very essential.</span></p>

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

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

<p style="text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16251271851625127185.jpg" style="height:780px; width:800px" /></p>

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

<p style="text-align:justify"><span style="font-size:14px">This is done by trip circuit supervision relays. An arrangement for this purpose is shown in figure 6.10. Assuming d. c. control supply to be 220 V d. c., auxiliary relay A is 220 V d. c. relay (i.e., it operates if 220 V d. c. is applied across its coil) and auxiliary relay B is 110 V d. c. relay. If the breaker is closed, 52-a<sub>1</sub> is closed. If the trip coil is healthy, relay A is energized energizing relay C (220 V d. c. relay) through contact A-1. An alarm will not be sounded as the NC contact of relay C opens out. Should the trip coil be open-circuited, A will not energize, C remains deenergized and alarm is sounded to let the control room staff know the fact. They should replace the trip coil. If the circuit breaker is open, 52-a<sub>1</sub> is open, but 52-a<sub>2</sub> is closed. Now relay coils of relays A and B will be in series if trip coil is healthy. 110 V d. c. is applied across both the relay coils. However, relay A will not operate as it is not getting sufficient voltage, but relay B will operate, B-1 will close, C is energized, and alarm will not be sounded. Alarm will be sounded if trip coil is unhealthy.</span></p>

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

<ol>
	<li style="text-align:justify">
	<p><span style="font-size:14px"><strong>&nbsp;Annunciators:</strong></span></p>
	</li>
</ol>

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">In major substations and power plants many kinds of faults and abnormalities occur. There must be proper indication for the operator to know exactly what kind of fault or abnormality has occurred so that he can guide the maintenance staff accordingly. For this purpose, the annunciators are developed.</span></p>

<p style="margin-left:48px; text-align:justify">&nbsp;</p>

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">An annunciator alarm equipment consists of a facia (or window) housing a number of indicating lamps of small d. c. voltage rating. Initiation of an alarm condition causes the concerned lamp in the facia to flash and an audible alarm is sounded. By pushing the &ldquo;accept&rdquo; pushbutton provided in front of the facia, the fault is accepted by the operator. This acceptance of an alarm steadies the flash-light and lamp will continuously glow. When the condition is repaired, the lamp extinguishes when reset by &ldquo;reset&rdquo; pushbutton provided in front of facia. Facias are designed to incorporate 6, 9, 12, 24 or more indications as per requirements.</span></p>