<p style="text-align:justify"><span style="font-size:14px">The ground relays are meant for sensing ground faults i.e., L-g and L-L-g faults. Following are the considerations while setting ground relays.</span></p>

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

<ol style="list-style-type:lower-alpha">
	<li style="text-align:justify">
	<p><span style="font-size:14px">A ground relay shall not operate for L-L-L or L-L fault, because, if it operates, it will be difficult for line maintenance staff to find the sustained fault while patrolling the line. It is one of the important functions of the protective relaying system to indicate the type of fault.</span></p>
	</li>
</ol>

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

<p style="margin-left:48px; text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16261742071626174207.jpg" style="height:555px; width:800px" /></p>

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

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

<p style="margin-left:48px; text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16261742481626174248.jpg" style="height:428px; width:800px" /></p>

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

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">A ground relay is connected in residual circuit of three line CTs as shown in figure 7.12. It can be very easily understood that the current flowing through a ground relay under normal operating conditions is zero (as vector sum of I<sub>R</sub>, I<sub>Y</sub> and I<sub>B</sub> is zero). Therefore, the plug-setting of a ground relay is not dependent on normal load current unlike phase relays. In case of L-L-L-g fault also, as I<sub>Rf</sub> + I<sub>Yf</sub> + I<sub>Bf</sub> = 0 (because L-L-L-g fault is a symmetrical fault), no current will pass through the ground relay. Therefore, ground relay does not operate for this fault. As such, ground relay should not operate for phase faults (L-L-L-g, L-L-L or L-L). The ground relay will not operate for L-L faults also. For Y-B fault, I<sub>Y</sub> = -I<sub>B</sub> and I<sub>R</sub> = 0 (pre-fault currents are assumed to be zero) which gives, I<sub>R</sub> + I<sub>Y</sub> + I<sub>B</sub> = 0. Hence, no current will flow through ground relay. Only zero sequence current can pass through ground relay which is a case for either L-g fault or L-L-g fault. Hence ground relay or earth-fault relay will operate for L-g faults and L-L-g faults only. The plug-setting (or sensitivity) of a ground relay is dependent on possible mismatch between three line CTs. In case of L-L-L-g fault, fault current will be very large (may be 10, 15 or 20 times the CMR of equipment or transmission line). The CTs may saturate because of this large current and magnetizing (saturation) characteristic of three line CTs may not be identical [as shown in figure 7.12(a)]. This would give rise to a spill current flowing through a ground relay causing unwanted operation (as ground relay should not operate for phase faults). Therefore, the plug-setting of a ground relay must be higher than this spill current due to mismatch of saturation characteristics of three line CTs.</span></p>

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

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16261742881626174288.jpg" style="height:616px; width:800px" /></span></p>

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

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16261743261626174326.jpg" style="height:727px; width:800px" /></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">If higher sensitivity of a ground relay is required, the ground relay can be connected in different ways as shown in figure 7.13(a) and 7.13(b). For connections as shown in figure 7.13(a), neutral point should be available on the terminal block of equipment (transformer). It is obvious that the current will flow through neutral circuit in case of L-g and L-L-g faults only. For connections as shown in figure 7.13(b), CBCT (Core Balance CT) is required and CBCT can be used in case of cables only and not in case of overhead lines. The clearance between R, Y and B phases for overhead lines is large and use of CBCT will require core of large diameter and there will be problems of leakage flux. Therefore, application of CBCT is restricted usually for 6.6 kV and 11 kV indoor switchgears.</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">Monitoring the ground relay by an undervoltage unit is usually not required or volage-controlled ground overcurrent relay is generally not used because zero sequence impedance of the system is very large. Also, zero sequence network is terminated at the nearest grounded transformer. The zero-sequence current varies with distance to fault and is not affected by variation in generating conditions.</span></p>

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

<ol start="2" style="list-style-type:lower-alpha">
	<li style="text-align:justify">
	<p><span style="font-size:14px">If L-g fault occurs very far from relaying point [some 100 km (or more) away in transmission line), the fault current magnitude will be very small.</span></p>
	</li>
</ol>

<p style="text-align:justify">&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="font-size:14px"><span class="math-tex">\(I_{Lg}=\frac{E}{Z_1+Z_2+Z_0+3Z_n+3Z_f}\)</span>, </span></p>

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

<p style="text-align:justify"><span style="font-size:14px">Where Z<sub>1</sub> = Positive Sequence Impedance.</span></p>

<p style="text-align:justify"><span style="font-size:14px">&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Z<sub>2</sub> = Negative Sequence Impedance.</span></p>

<p style="text-align:justify"><span style="font-size:14px">&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Z<sub>0</sub> = Zero Sequence Impedance.</span></p>

<p style="text-align:justify"><span style="font-size:14px">&nbsp;Z<sub>n</sub> = Deliberate Impedance Connected in the Neutral Circuit.</span></p>

<p style="text-align:justify"><span style="font-size:14px">&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Z<sub>f</sub> = Fault Resistance.</span></p>

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

<p style="text-align:justify"><span style="font-size:14px">For transmission line, Z<sub>1</sub> = Z<sub>2</sub> and for E. H. V. lines, Z<sub>0</sub> is approximately 4 times Z<sub>1</sub>. Even if we assume Z<sub>n</sub> to be zero, Z<sub>f</sub> is quite large as,</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">Z<sub>f</sub> = R<sub>f</sub> = Resistance of flash-over path + Resistance of iron tower + Tower footing Resistance.</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">In case of asphalt surfaces (hilly areas), the tower footing resistance (or soil resistivity) would be quite large resulting in Z<sub>f</sub> equal to 20 ohms (or in worst case even 50 ohms). Thus, fault current magnitude can be even less than normal full load current. Hence, the setting range of ground relays is available as 5-20 %, 10-40 % and 20-80 % of relay rating (in seven equal steps).</span></p>

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

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16261743801626174380.jpg" style="height:494px; width:800px" /></span></p>

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

<ol start="3" style="list-style-type:lower-alpha">
	<li style="text-align:justify">
	<p><span style="font-size:14px">If there is a delta-wye transformer between two successive relays (usually in power system, the delta-wye transformers are there between two successive relays as voltage is required to be generally stepped down to meet with economic voltage of transmission unless the substation is just a switching substation), a ground fault on star connected secondary is not reflected on delta connected primary side. L-g fault on star connected secondary side will be seen as L-L fault on primary side. Hence, ground relay on primary side cannot sense the fault (refer figure 7.14). Two successive relays are, then, independent and need not be coordinated. The demerit, because of this fact is that the relay on source side will not give back-up to a relay on load side. A ground relay connected across neutral CT as shown in figure 7.13(a) will give back-up to a ground relay connected in residual circuit of three line CTs.</span></p>
	</li>
</ol>

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

<p style="margin-left:48px; text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16292788101629278810.jpg" style="height:489px; width:800px" /></p>

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

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">Because of this fact, referring to figure 7.5,</span></p>

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px"><span class="math-tex">\(P.S.of\hspace{0.2cm} ground\hspace{0.2cm} relay\hspace{0.2cm} R_2 \)</span></span></p>

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px"><span class="math-tex">\(&gt;\frac{1.3}{1.05}\times P.S. of\hspace{0.2cm}ground\hspace{0.2cm}relay\hspace{0.2cm}R_3\)</span></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">only if there is no delta-wye transformer intervening between relays R<sub>2</sub> and R<sub>3</sub>. Also ground relay R<sub>2</sub> is to be made to reach up to bus D only if there is no delta-wye transformer between relay R<sub>2</sub> and bus D. Relay R<sub>2</sub> can be set independent of relay R<sub>3</sub> and TMS of R<sub>2</sub> can be less than that of R<sub>3</sub>. Relay R<sub>2</sub> can be set to operate even instantaneously if need be. All these arguments hold for coordination between relays R<sub>1</sub> and R<sub>2</sub> also.</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">As delta-wye transformer is usually there between two successive relays, the requirements to satisfy rule 2 and 3 of phase relays do not hold good for ground relays. Moreover, for time setting, the time of operation of R<sub>2</sub> = time of operation of R<sub>3</sub> + 0.25, only if there is no transformer intervening between relays R<sub>2</sub> and R<sub>3</sub>.</span></p>

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

<ol start="4" style="list-style-type:lower-alpha">
	<li style="text-align:justify">
	<p><span style="font-size:14px">The fourth consideration is with reference to excitation current of CTs. While calculating plug-setting, we were referring all calculations in terms of CT primary. This means that if plug-setting of a relay is 100 % (of 1 amp), it is 1 amp. If the relay is connected across secondary of 100/1 amp CT, the plug-setting is 100 amp in primary terms. But this statement is not fully correct as 100 amp in primary is not transformed as 1 amp. Because of excitation current (let us assume a realistic value of 0.05 amp) of CT, 100 amp is transformed as 0.95 (1.0 &ndash; 0.05) amp. Therefore, when we say 100 % plug-setting means 100 amp in primary, there is an error of approximately 5 %. In this case, 100 % mean 105 amp in primary and not 100 amp. This error was ignored in all earlier calculations as the error is quite small.</span></p>
	</li>
</ol>

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

<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">With ground relays this error is quite large. If there is an L-g fault, the current in secondary of CT due to this fault will have to feed excitation current requirement of all the three line CTs plus the current juice for operation of a ground relay. For 100/1 CT, if 25 amp is the magnitude of fault current for L-g fault, it will be reflected as 0.25 amp out of which 0.15 (3 times 0.05) amp will be required to excite the cores of the CTs and remnant 0.1 amp (which means 10 % of 1 amp) will flow through the ground relay. Thus, if 10 % is the plug setting of a ground relay, it means 25 amp in primary of a CT (which means 25 % of 100 amp rating). The effect of excitation current of CTs on sensitivity of a ground relay is demonstrated in table 7.4 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:47px; width:900px">
	<caption>
	<p><strong><span style="font-size:18px">Table 7.4: Effect of Excitation Current of CTs on Sensitivity of a Ground Relay</span></strong></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:59px">
			<div style="text-align:center"><strong><span style="font-size:28px">P. S. of Ground Relay</span></strong></div>

			<div style="text-align:center"><strong><span style="font-size:28px">%</span></strong></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:82px">
			<div style="text-align:center"><strong><span style="font-size:28px">P. S. of Ground Relay in Amp </span></strong></div>

			<div style="text-align:center"><strong><span style="font-size:28px">CT sec = 1 Amp</span></strong></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:80px">
			<div style="text-align:center"><strong><span style="font-size:28px">3 I<sub>e</sub> =</span></strong></div>

			<div style="text-align:center"><strong><span style="font-size:28px">3 &times;&nbsp;0.05 = 0.15 Amp</span></strong></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:85px">
			<div style="text-align:center"><strong><span style="font-size:28px">CT Secondary Current in Amp</span></strong></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:83px">
			<div style="text-align:center"><strong><span style="font-size:28px">CT Primary Current (100/1 CT)</span></strong></div>

			<div style="text-align:center"><strong><span style="font-size:28px">Amp</span></strong></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:84px">
			<div style="text-align:center"><strong><span style="font-size:28px">Sensitivity of a Relay in CT Primary Terms</span></strong></div>

			<div style="text-align:center"><strong><span style="font-size:28px">%</span></strong></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:81px">
			<div style="text-align:center"><strong><span style="font-size:28px">% Error</span></strong></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:59px">
			<div style="text-align:center"><span style="font-size:28px">Q</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:82px">
			<div style="text-align:center"><span style="font-size:28px">X</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:80px">
			<div style="text-align:center"><span style="font-size:28px">Y</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:85px">
			<div style="text-align:center"><span style="font-size:28px">X + Y</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:83px">
			<div style="text-align:center">&nbsp;</div>
			</td>
			<td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:84px">
			<div style="text-align:center"><span style="font-size:28px">P</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:81px">
			<div>&nbsp;</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:59px">
			<div style="text-align:center"><span style="font-size:28px">5</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:82px">
			<div style="text-align:center"><span style="font-size:28px">0.05</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:80px">
			<div style="text-align:center"><span style="font-size:28px">0.15</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:85px">
			<div style="text-align:center"><span style="font-size:28px">0.2</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:83px">
			<div style="text-align:center"><span style="font-size:28px">20</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:84px">
			<div style="text-align:center"><span style="font-size:28px">20</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:81px">
			<div style="text-align:center"><span style="font-size:28px">300</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:59px">
			<div style="text-align:center"><span style="font-size:28px">10</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:82px">
			<div style="text-align:center"><span style="font-size:28px">0.10</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:80px">
			<div style="text-align:center"><span style="font-size:28px">0.15</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:85px">
			<div style="text-align:center"><span style="font-size:28px">0.25</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:83px">
			<div style="text-align:center"><span style="font-size:28px">25</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:84px">
			<div style="text-align:center"><span style="font-size:28px">25</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:81px">
			<div style="text-align:center"><span style="font-size:28px">150</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:59px">
			<div style="text-align:center"><span style="font-size:28px">20</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:82px">
			<div style="text-align:center"><span style="font-size:28px">0.2</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:80px">
			<div style="text-align:center"><span style="font-size:28px">0.15</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:85px">
			<div style="text-align:center"><span style="font-size:28px">0.35</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:83px">
			<div style="text-align:center"><span style="font-size:28px">35</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:84px">
			<div style="text-align:center"><span style="font-size:28px">35</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:81px">
			<div style="text-align:center"><span style="font-size:28px">75</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:59px">
			<div style="text-align:center"><span style="font-size:28px">40</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:82px">
			<div style="text-align:center"><span style="font-size:28px">0.4</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:80px">
			<div style="text-align:center"><span style="font-size:28px">0.15</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:85px">
			<div style="text-align:center"><span style="font-size:28px">0.55</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:83px">
			<div style="text-align:center"><span style="font-size:28px">55</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:84px">
			<div style="text-align:center"><span style="font-size:28px">55</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:81px">
			<div style="text-align:center"><span style="font-size:28px">37.5</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:59px">
			<div style="text-align:center"><span style="font-size:28px">80</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:82px">
			<div style="text-align:center"><span style="font-size:28px">0.8</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:80px">
			<div style="text-align:center"><span style="font-size:28px">0.15</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:85px">
			<div style="text-align:center"><span style="font-size:28px">0.95</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:83px">
			<div style="text-align:center"><span style="font-size:28px">95</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:84px">
			<div style="text-align:center"><span style="font-size:28px">95</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:81px">
			<div style="text-align:center"><span style="font-size:28px">18.75</span></div>
			</td>
		</tr>
	</tbody>
</table>

<p>&nbsp;</p>

<p>&nbsp;</p>

<p style="text-align:justify"><span style="font-size:14px">In table as above, last column is calculated as, % Error&nbsp;<span class="math-tex">\(=\frac{P-Q}{Q}\times 100.\)</span></span></p>

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

<p style="text-align:justify"><span style="font-size:14px">This means that too sensitive (say 5 %) setting of a ground relay does not provide that nice sensitivity when referred to primary terms. Hence, higher sensitivity should be selected when it is really required. If the ground relay is connected as shown in figure 7.13(a) or 7.13(b), the error in sensitivity will reduce as there is only one CT core. The multiplying factor, in this case, will be 1 instead of 3.</span></p>