Engineering Pro Guides Question 32

[eatsleep]

Can anyone help me with the below question, it seems like such an easy concept but i can't quite wrap my mind around this one. 

 

[roy167]

I think their answer may be confusing you. The old transmission line impedance before the step up transformer was installed is 10< 30 on 13.2 KV

Now the transformer is installed so transmission line will see 132 KV 

You calculate new impedance using the new voltage

Z new = Z old X (old voltage /New Voltage) ^2 

The difference in impedance will be magnitude of (Z old - Z new) or vice versa. I think their answer showing some operation on Z old which was not needed. You keep Z old as it is, calculate Z new using the new voltage base.  Power base is same in old case and new case, so you can ignore that.  They got Z old and Z new little mixed up and confusing people. 

 

[eatsleep]

@roy167 yep thats it, thanks for the explanation.

 

[RadioBox]

I think their answer may be confusing you. The old transmission line impedance before the step up transformer was installed is 10< 30 on 13.2 KV

Now the transformer is installed so transmission line will see 132 KV 

You calculate new impedance using the new voltage

Z new = Z old X (old voltage /New Voltage) ^2 

The difference in impedance will be magnitude of (Z old - Z new) or vice versa. I think their answer showing some operation on Z old which was not needed. You keep Z old as it is, calculate Z new using the new voltage base.  Power base is same in old case and new case, so you can ignore that.  They got Z old and Z new little mixed up and confusing people. 

That's a great explanation. Makes sense. The technical guide's solution tripped me up at first too.