Complex Imaginary Volume 3, Problem #68

[jcbabb]

I have a question regarding a given solution. Given the following parameters, can you show me the work to find the transformer's efficiency?

Given Tx:

20kVA

6.6/2.8 kV

Core Loss = 75 W

Copper Loss = 241 W

Is = 6.6<-22 A , where Is = secondary current

The formula I would use is:

Eff = Pout/(Pout + P losses)

Eff = (2.8 kV)(6.6 A)(cos(-22)/[((2.8 kV)(6.6 A)(cos(-22))+75+241] , where I get Pout = 18.479.28 kW

Eff = 98.3%

The closest answer is 98.2% (which is also marked as the correct answer), but the solution shows that Pout = 17.1 kW.

Has anyone else come across this difference?

 

[Wael]

check your math again:

2.4K * 6.6 * cos -22 = 17.1KW

 

[jcbabb]

It's never a bad time to make sure that your calculator is in degrees and not radians.

Amazing.

Thanks for checking the math!!!