# 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
5
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.

3. ### WBahn Moderator

Mar 31, 2012
17,743
4,795
It looks like you tried to include a link to a third-party site for the image. It's strongly preferred that you not do that. First, a lot of those links don't work well (like this one) and, second, your post will be archived for years/decades. What are the chances that the image you have on the third-party site will still be accessible then? Furthermore, many of these sites require registration, most of them try to load dozens (yes, dozens, if not many dozens) of cookies onto your machine since they are almost always advertisement supported, some of them try to load application software onto your machine, and some of them are downright malicious and are nothing but fronts for getting malware onto peoples' machines.

The proper way to do it is to upload your images directly to the AAC server. You can do this by "Going Advanced" (if you aren't already) and using the Manage Attachments button in the "Additional Options" dialog.

The "end of the transmissions line" is out of context without the word before it: "sending end of the transmissions line". Your transmission lines connect generators to your loads. There are two ends. Which end is most reasonably described as the sending end?