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A 2-bus system and corresponding zero sequence network are shown in the figure. The transformers T1 and T2 are connected as

A 2-bus system and corresponding zero sequence network are shown in the figure. The transformers T1 and T2 are connected as Correct Answer <img alt="Gate EE Power System Mobile Ques-72 Q-3" src="//storage.googleapis.com/tb-img/production/15/08/Gate%20EE_Power%20System_Mobile_Ques-72_Q-3.PNG" style="height:29px; width:120px">

Concept:

Zero sequence networks for different 3-phase loads are shown below.

[ alt="F1 Nakshatra Anil 24-06.21 D1" src="//storage.googleapis.com/tb-img/production/21/06/F1_Nakshatra_Anil_24-06.21_D1.png" style="width: 551px; height: 279px;">

The zero sequence equivalent circuits of 3-phase transformers can be drawn by using the following general circuit.

[ alt="F1 Nakshatra Anil 24-06.21 D2" src="//storage.googleapis.com/tb-img/production/21/06/F1_Nakshatra_Anil_24-06.21_D2.png" style="width: 301px; height: 117px;">

Z is the zero-sequence impedance of the windings of the transformer. These are two series and two shunt switches. One series and one shunt switches are for both sides(primary and secondary) separately.

The series switch of a particular side is closed if it is star grounded and the shunt switch is closed if that side is delta connected, otherwise, they are left open.

Application:

Given two bus system,

[ alt="Gate EE Power System Mobile Ques-72 Q-1" src="//storage.googleapis.com/tb-img/production/15/08/Gate%20EE_Power%20System_Mobile_Ques-72_Q-1.PNG" style="height: 296px; width: 473px;">

The zero-sequence network of the corresponding transformers will be 

[ alt="Gate EE Power System Mobile Ques-72 A-1" src="//storage.googleapis.com/tb-img/production/15/08/Gate%20EE_Power%20System_Mobile_Ques-72_A-1.PNG" style="height:66px; width:269px">

[ alt="Gate EE Power System Mobile Ques-72 A-2" src="//storage.googleapis.com/tb-img/production/15/08/Gate%20EE_Power%20System_Mobile_Ques-72_A-2.PNG" style="height:118px; width:311px">

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