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1004 ⏐⏐⏐ POLYPHASE SYSTEMS<br />

Using determinants, we have<br />

� E AB Z 2 �<br />

� E BC �(Z 2 � Z 3)�<br />

I an � ––––––––––––––––––––––<br />

�Z 1 � Z 2 Z 2 �<br />

� �Z 2 �(Z 2 � Z 3)�<br />

�<br />

�(Z 2 � Z 3)E AB � E BCZ 2<br />

����<br />

�Z 1Z 2 � Z 1Z 3 � Z 2Z 3 � Z 2 2 � Z 2 2<br />

�Z2(EAB � EBC) � Z3EAB Ian ����<br />

�Z1Z2 � Z1Z3 � Z2Z3 Applying Kirchhoff’s voltage law to the line voltages:<br />

E AB � E CA � E BC � 0 or E AB � E BC ��E CA<br />

Substituting for (E AB � E CB) in the above equation for I an:<br />

I an �<br />

�Z 2(�E CA) � Z 3E AB<br />

���<br />

�Z 1Z 2 � Z 1Z 3 � Z 2Z 3<br />

E ABZ 3 � E CAZ 2<br />

and Ian � ���<br />

(22.38)<br />

Z1Z2 � Z1Z3 � Z2Z3 In the same manner, it can be shown that<br />

E CAZ 2 � E BCZ 1<br />

Icn � ���<br />

(22.39)<br />

Z1Z2 � Z1Z3 � Z2Z3 Substituting Eq. (22.39) for I cn in the right-hand side of Eq. (22.37b),<br />

we obtain<br />

E BCZ 1 � E ABZ 3<br />

Ibn � ���<br />

(22.40)<br />

Z1Z2 � Z1Z3 � Z2Z3 EXAMPLE 22.9 A phase-sequence indicator is an instrument that can<br />

display the phase sequence of a polyphase circuit. A network that will<br />

perform this function appears in Fig. 22.37. The applied phase sequence<br />

is ABC. The bulb corresponding to this phase sequence will burn more<br />

brightly than the bulb indicating the ACB sequence because a greater<br />

current is passing through the ABC bulb. Calculating the phase currents<br />

will demonstrate that this situation does in fact exist:<br />

1<br />

Z1 � XC � ���� �166 �<br />

(377 rad/s)(16 � 10<br />

By Eq. (22.39),<br />

�6 1<br />

�<br />

qC<br />

F)<br />

Icn �<br />

(200 V �120°)(200 � �0°) � (200 V ��120°)(166 � ��90°)<br />

�����������<br />

(166 � ��90°)(200 � �0°) � (166 � ��90°)(200 � �0°) � (200 � �0°)(200 � �0°)<br />

Icn �<br />

ECAZ2 � EBCZ1 ���<br />

Z1Z2 � Z1Z3 � Z2Z3

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