# Problem 8.1



## Wolverine (Oct 20, 2006)

A 3000KVA, 150V machine has p.u. impedance of .1 + j.6. Determine the actual impedance of the machine.


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## Art (Oct 20, 2006)

> A 3000KVA, 150V machine has p.u. impedance of .1 + j.6. Determine the actual impedance of the machine.


0.00075 + 0.0045 j


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## singlespeed (Oct 20, 2006)

4.56 &lt;80.5o mohm


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## benbo (Oct 20, 2006)

Is that 150V or 150KV ?


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## Art (Oct 20, 2006)

> Is that 150V or 150KV ?


if 150 kv

the pu base changes by a factor of 1,000,000 (edited from 1000)

750 + 4500 j ohms


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## benbo (Oct 20, 2006)

Don't you square the voltage to get the base impedance?

Wouldn't that be a factor of a million?

I passed the exam but I hate pu. And I know this is about as easy as it gets.

It just seemed like a small impedance for so much current, that's why I questioned the 150 V.


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## Art (Oct 20, 2006)

> Don't you square the voltage to get the base impedance?
> Wouldn't that be a factor of a million?
> 
> I passed the exam but I hate pu.? And I know this is about as easy as it gets.
> ...


yep would be 1,000,000:

I base = 3,000,000 VA/150 V = 20,000 A

Z base = 150 V/20,000 A (I base) = 150 V ^2/3,000,000 VA = 0.0075 ohm

I base = 3,000,000 VA/150,000 V = 20 A

Z base = 150,000 V/20 A (I base) = 150,000 V ^2/3,000,000 VA = 7500 ohm

7500/0.0075 = 1,000,000

either way it does not make much sense for a real world machine...

w/150 kV

750 + 4500 j ohms


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