# A Power System problem : 3 phase transformer AND two loads

Discussion in 'Homework Help' started by AboRoman, Dec 21, 2013.

1. ### AboRoman Thread Starter New Member

Dec 9, 2011
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0
I did my best with it and I do have an idea how to solve but at some point I got confused a bit, here is the problem:

A 2400/240-V two-winding transformer has the following parameters,

Req = 0.64 Ohm
Xeq = 0.66 Ohm

Both Req and Xeq are referred to the primary. The core resistance and the magnetization reactance are neglected.

Three of the above single phase transformers are connected as a 3-phase transformer bank. The high voltage side of the transformer bank is connected in Y and the power is supplied to the transformer bank through a transmission line with an impedance equal to ZTL = j 2 Ohm.

The transformer bank is supplying two different three-phase loads connected to the 240 V side of the transformer bank as follows,

Load 1: 100 kVA, 0.85 p.f lagging.
Load 2: 80 kW, 0.9 p.f leading.

a) Determine the rating of the transformer bank (KVA) to supply the above load.

b) Calculate the voltage and current of the sending end of the transmission line.

c) Calculate the p.f. at the sending end of the transmission lines.

d) Based on your calculation in (c), what is the kVAR rating of a three-phase capacitance (or inductance) load to be connected to the secondary side of the transformer to improve the p.f. in (c) to 0.95 lagging.

okay, that was the question, I started by the following:

the above is the approximated equivalent circuit with a = 2400/240=10
and then proceeded to draw the whole system .. I'm not sure if I did draw the system correctly !

for part (a) I think I know how to do it, I should find the current from load 1 by : I = S/(3x2400)
and for load 2 by : I = P/(3x2400x-0.9)

but for part (b) and (c) I was not able to understand how to do it, what does he mean by the end of transmission lines ?! how can achieve that ?

2. ### jegues Well-Known Member

Sep 13, 2010
735
43
Post your drawing and show complete calculations for part (a). Only then will we be able to help you.

Mar 31, 2012
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