<p style="text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16256461661625646166.jpg" style="height:616px; width:800px" /></p>

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

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

<p style="text-align:justify"><span style="font-size:14px">Figure 7.38 shows a single line diagram of a portion of a power system network. The relays R<sub>1</sub> to R<sub>7</sub> are normal inverse IDMT overcurrent relays with usual range. All four induction motors are identical with ratings as follows:</span></p>

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">Three-phase, 11 kV, 2000 hp, efficiency = 90 %, 0.85 pf, overload withstand = 110 % of rated current.</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">The fault currents for faults at different buses are tabulated below:</span></p>

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

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

<table cellspacing="0" class="MsoTableGrid" style="border-collapse:collapse; border:none; margin-left:104px; width:900px">
	<caption>
	<p><span style="font-size:14px"><strong>Table 7.15: Fault Currents at Different Buses</strong></span></p>
	</caption>
	<tbody>
		<tr>
			<td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:129px">
			<div style="text-align:center"><span style="font-size:28px">Bus</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:155px">
			<div style="text-align:center"><span style="font-size:28px">Fault Current for Triple Line Fault in Amp</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:170px">
			<div style="text-align:center"><span style="font-size:28px">Fault Current for Double Line Fault in Amp</span></div>
			</td>
		</tr>
		<tr>
			<td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:129px">
			<div style="text-align:center"><span style="font-size:28px">A</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:155px">
			<div style="text-align:center"><span style="font-size:28px">4860</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:170px">
			<div style="text-align:center"><span style="font-size:28px">4208</span></div>
			</td>
		</tr>
		<tr>
			<td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:129px">
			<div style="text-align:center"><span style="font-size:28px">B</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:155px">
			<div style="text-align:center"><span style="font-size:28px">2754</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:170px">
			<div style="text-align:center"><span style="font-size:28px">2385</span></div>
			</td>
		</tr>
		<tr>
			<td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:129px">
			<div style="text-align:center"><span style="font-size:28px">C</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:155px">
			<div style="text-align:center"><span style="font-size:28px">10139</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:170px">
			<div style="text-align:center"><span style="font-size:28px">8780</span></div>
			</td>
		</tr>
		<tr>
			<td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:top; width:129px">
			<div style="text-align:center"><span style="font-size:28px">D</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:155px">
			<div style="text-align:center"><span style="font-size:28px">3983</span></div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:170px">
			<div style="text-align:center"><span style="font-size:28px">3450</span></div>
			</td>
		</tr>
	</tbody>
</table>

<p>&nbsp;</p>

<p>&nbsp;</p>

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">TMS of R<sub>7</sub> and R<sub>5</sub> are set at 0.1 and 0.3 respectively and the high-set instantaneous setting of relays R<sub>5</sub> and R<sub>3</sub> are set at 700 % and 2000 % of the relay rating respectively. Allow 10 % overload while deciding plug-setting of all relays. Relay R<sub>1</sub> is voltage-controlled overcurrent relay such that its plug-setting reduces to 40 % of set value if voltage collapses below 70 % of rated voltage. Assume</span></p>

<ul>
	<li style="text-align:justify">
	<p><span style="font-size:14px">1 hp = 735.5 Watts.</span></p>
	</li>
	<li style="text-align:justify">
	<p><span style="font-size:14px">Instantaneous time of operation of relays = 0.06 sec.</span></p>
	</li>
</ul>

<p>&nbsp;</p>

<p><span style="font-size:14px"><strong>P. S. of phase relay R<sub>7</sub> shall be set at</strong></span></p>