<p style="text-align:justify"><span style="font-size:14px">There are more than one setting groups in modern numerical relays. As many as six groups are available in the relays manufactured by renowned relay manufacturers. This change in setting as per requirement makes the relay practically adaptive to dynamic nature of power system. Also, relaying system offers much better protection and more sensitive and faster protection. Some case studies are discussed as follows to understand the above statement.</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/16256301001625630100.jpg" style="height:816px; width:800px" /></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/16256301601625630160.jpg" style="height:523px; width:800px" /></span></p>

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	<p><span style="font-size:14px"><strong><u>Varying Generating Conditions:</u></strong> Power system is not static. It is dynamic. The normal power flow and fault currents are changing based on system conditions. The relay setting is required to adapt with this change in power system conditions. The conventional electromechanical or static relays were not capable to offer multiple groups of settings. Numerical relay offers these multiple groups of settings. One such dynamism of power system is varying generating conditions as shown in 7.30(a). Generating conditions vary based on variations of load as per load curve. If one or more generators are required to be tripped as per reduced load demand, the normal rated current flow through the transmission line varies. Also, the fault current is variable based on number of generators connected to the bus. Hence, plug-setting and time setting of overcurrent relay R are the functions of generating conditions. These can be changed accordingly as multiple sets are available in numerical relay. In earlier days, when this facility was not available, the plug-setting (only one setting value was available) was decided based on maximum possible power flow. Hence, during less power flow, say at night, the relay was less sensitive. Also, during day hours, when all generators are ON, Z<sub>s</sub>/Z<sub>l</sub> ratio is small because Z<sub>s</sub> is small. Therefore, relay R can be normal inverse overcurrent relay. But during night hours, when two (or probably 3) generators are tripped, Z<sub>s</sub> is large resulting in Z<sub>s</sub>/Z<sub>l</sub> ratio more than or equal to 2, necessitating relay R to be a very inverse relay. This dynamic change could not be done in earlier relays. But with the advent of numerical relays this is possible because in first setting group, it behaves as normal inverse relay and in second setting group, it will change its role as very inverse relay. This dynamic change can be automatic also through the binary input, if binary input is configured for change of setting group. As shown in figure 7.30(b), when any of the generator trips, the relevant breaker (say CB<sub>1</sub>) will trip. The NC auxiliary switch of that breaker can be wired in control circuit to extend 220 V D. C. to binary input to change the setting group. Thus, at different hours, the relay setting changes, increasing the relay sensitivity and faster protection. Thereby, the protection is better and more efficient. No doubt, this case study assumes that the generating plant is gas turbine plant or diesel power plant (or any other which can be switched OFF and ON fast). The thermal power plant or nuclear power plant cannot be switched OFF or ON fast.</span></p>
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</ul>

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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/16256302031625630203.jpg" style="height:495px; width:800px" /></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/16256302351625630235.jpg" style="height:340px; width:800px" /></span></p>

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	<p><span style="font-size:14px"><strong><u>Parallel Feeder Protection:</u></strong> We have already discussed that, in case of parallel feeder fed from one end, relays R<sub>3</sub> and R<sub>4</sub> are directional overcurrent relays with operative direction as shown by arrowheads in the figure 7.31(a). Plug-setting of relays R<sub>1</sub>/R<sub>2</sub> shall be based on one-line contingency, i.e., 100 % of 1 amp with the details given in figure 7.31(a). TMS is to be decided based on highest fault current, i.e., both the feeders in circuit. But when both the lines are in operation, the load current per line is 500 amp and hence, the relay sensitivity is less and as the PSM will be lower, time of operation of the relay will be more. This was the status when conventional relays were used. If numerical relays are installed and commissioned, the two sets of plug-setting can be set, one with both feeders ON and second with one of the feeders tripping due to fault. That means 50 % in first case and 100 % in second case. Consequently, there will be two sets of TMS as well. The setting of relays R<sub>3</sub>/R<sub>4</sub> will also be, accordingly, in two groups. The change in group can be automatic if the change is routed through binary input configuration as suggested by figure 7.31(b).</span></p>
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</ul>

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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/16256302781625630278.jpg" style="height:728px; width:800px" /></span></p>

<p style="text-align:justify"><span style="font-size:14px">???????</span></p>

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	<p><span style="font-size:14px"><u>S<strong>ingle Bus Scheme with Sectionalizing Breaker</strong>:</u> In this case, the settings of relays R<sub>1</sub>/R<sub>2</sub> are the functions of status of the sectionalizing breaker, i.e., whether it is ON or OFF. The normal current flow will be different in both cases and fault current will also be different as when the sectionalizing breaker is ON, two incomers I<sub>1</sub> and I<sub>2</sub> shown in figure 7.32 are in parallel, but with sectionalizing breaker OFF, they are not in parallel. The fault current in first case will be more than that in the other case. Hence, there will be two groups of settings (P. S. and TMS) for relays R<sub>1</sub>/R<sub>2</sub>.</span></p>
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<p style="text-align:justify"><span style="font-size:14px">???????</span></p>

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	<p><span style="font-size:14px"><strong><u>Application of Adaptive Relaying in Ring Network:</u></strong> </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/16256304321625630432.jpg" style="height:575px; width:800px" /></span></p>

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	<p><span style="font-size:14px">Referring to figure 7.33, there are four different conditions of the network:</span></p>
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			<p><span style="font-size:14px">Lines L<sub>1</sub>, L<sub>2</sub> and L<sub>3</sub> are in operation.</span></p>
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			<p><span style="font-size:14px">Line L<sub>1</sub> is out of operation due to forced outage. But lines L<sub>2</sub> and L<sub>3</sub> are in operation.</span></p>
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			<p><span style="font-size:14px">Similarly, L<sub>3</sub> is not in operation but L<sub>1</sub>-L<sub>2</sub> are in operation.</span></p>
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			<p><span style="font-size:14px">L<sub>2</sub> is tripped, L<sub>1</sub>-L<sub>3</sub> working.</span></p>
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		</ol>
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</ol>

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<p style="margin-left:48px; text-align:justify"><span style="font-size:14px">The power flow in all the three lines will be different in these four cases and hence, we shall use four groups of settings available in relays. We have yet not considered forced out ages of generators of the system. The system behaviour will be very dynamic and there will be many combinations of relay settings required. All relays R<sub>1</sub> to R<sub>6</sub> are required to be properly configured to be set for different setting groups as per requirement.</span></p>