<p style="text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16251290591625129059.jpg" style="height:499px; width:800px" /></p>

<p style="text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16251291051625129105.jpg" style="height:415px; width:800px" /></p>

<p style="text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16251291291625129129.jpg" style="height:1155px; width:800px" /></p>

<p style="text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16251291971625129197.jpg" style="height:353px; width:800px" /></p>

<p style="text-align:justify">&nbsp;</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">In directional relays, the phase angle between voltage and current vectors is to be compared. In phase comparator distance relays also, the phase angle between two electrical quantities is to be compared. Two-input phase comparator can be realized by static circuitry as shown in block diagram of figure 6.25. Two inputs A and B are first filtered to avoid harmonics as the distorted waveshape may lead to wrong zero crossing detection. A zero-crossing detector convers the sinusoidal wave into the square wave. The zero-crossing detector circuit is shown in figure 6.26. The zero-crossing detector is an op-amp comparing the input signal with earth as a reference. When the input is more than zero, the output is there, which is a square wave as shown in figure 6.27. The output of zero-crossing detector is differentiated and then rectified to clip off the negative spikes as shown in waveshapes of figure 6.27. Op-amp can be used as a differentiator or alternatively, a circuit shown in figure 6.28 can also be used. The output of the differentiator is fed to the monostable multivibrator, the band width of the square wave being adjusted to 5 milliseconds (90<sup>0</sup> in 50 Hz system). The output of the square wave for both the inputs are fed to an AND gate so that there will be output of the AND gate only if the phase difference between two quantities A and B is less than 90<sup>0</sup>. The output of the AND gate is fed to an output circuit consisting of thyristor via a differentiator. Tripping of a breaker will be established when the thyristor triggers.</span></p>