<ol start="1">
	<li>
	<p style="text-align:justify"><span style="font-size:14px">Manufacturers usually specify the impedance values of the equipment in pu of the rating of the Equipment.</span></p>
	</li>
	<li>
	<p style="text-align:justify"><span style="font-size:14px">Per unit data representation yields important information about relative magnitudes.</span></p>
	</li>
	<li>
	<p style="text-align:justify"><span style="font-size:14px">In power system there are large number of transformers. The ohmic value of impedance as referred to secondary is different from the value as referred to primary. But the pu values on both the sides are same. This simplifies the calculation of fault currents.</span></p>
	</li>
</ol>

<p>&nbsp;</p>

<p style="text-align:justify"><span style="font-size:14px">Ohmic value of the equivalent impedance referred to primary of transformer = Z<sub>1</sub></span></p>

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

<p style="text-align:justify"><span style="font-size:14px">Ohmic value of the equivalent impedance referred to secondary of transformer = Z<sub>2</sub></span></p>

<p>&nbsp;</p>

<p style="text-align:justify"><span style="font-size:14px">We know that,</span></p>

<p style="text-align:justify"><span style="font-size:14px">Z<sub>2</sub> = Z<sub>1</sub>K<sup>2</sup></span></p>

<p style="text-align:justify"><span style="font-size:14px">Where&nbsp;&nbsp;<span class="math-tex">\(K=\frac{V_2}{V_1}\)</span></span></p>

<p style="text-align:justify"><span style="font-size:14px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;V<sub>1</sub> = Primary Voltage</span></p>

<p style="text-align:justify"><span style="font-size:14px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;V<sub>2</sub> = Secondary Voltage</span></p>

<p style="text-align:justify"><span style="font-size:14px">pu Z <span class="math-tex">\(=\frac{IZ}{V}\)</span>&nbsp;</span></p>

<p style="text-align:justify"><span style="font-size:14px">Where&nbsp; I = Full load rated current of the transformer.</span></p>

<p style="text-align:justify"><span style="font-size:14px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Z = Equivalent Impedance in ohms.</span></p>

<p style="text-align:justify"><span style="font-size:14px">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; V = Rated Voltage.</span></p>

<p>&nbsp;</p>

<p style="text-align:justify"><span style="font-size:14px">pu Z referred to secondary,</span></p>

<p style="text-align:justify"><span class="math-tex">\(=\frac{I_2Z_2}{V_2}=\frac{I_2Z_1K^2}{V_2}=\frac{Z_1\frac{V_2^2}{V_1^2}}{\frac{V_2}{I_2}}\)</span></p>

<p style="text-align:justify"><span class="math-tex">\(=\frac{Z_1V_2^2I_2}{V_2V_1^2}=\frac{Z_1V_2^2I_1V_1}{V_2V_1^2V_2} \\\)</span>&hellip;&hellip;&nbsp;As&nbsp;&nbsp;<span class="math-tex">\(\frac{V_2}{V_1}=\frac{I_1}{I_2}\)</span></p>

<p style="text-align:justify"><span class="math-tex">\(=\frac{I_1Z_1}{V_1}=\)</span>&nbsp;<span style="font-size:14px">pu Z referred to primary.</span></p>

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

<p style="text-align:justify"><span style="font-size:14px">Hence pu values are same on both sides of transformer.</span></p>