Finding the supply voltage in a single phase transformer (Urgent)

Discussion in 'Homework Help' started by Oscar Vazquez, Feb 13, 2015.

1. Oscar Vazquez Thread Starter New Member

Feb 13, 2015
4
0
I have worked this out and compared to other colleagues and they are getting different answers that do not match up to the turn ratios, and I am getting tired of this problem.

A single-phase distribution transformer supplies four houses. The maximum load is 12 kW at a power factor of 0.78 (lagging). The load voltage is 235 V. The transformer rating is 20 kVA, with a primary voltage of 7.2 kV, a secondary voltage of 240 V, and a leakage reactance of 12%. Calculate the transformer supply voltage.

I've worked it out but I'm not sure its correct because you are given a leakage reactance in the problem, but it does not need to be used. 2. t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
Of course the leakage reactance must be used.

Feb 13, 2015
4
0

Feb 13, 2015
4
0
5. t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
You've lost me. Your original question states that the load voltage is 235V. Post the question exactly as asked, then it might be possible to answer intelligently.

6. Oscar Vazquez Thread Starter New Member

Feb 13, 2015
4
0
I apologize, I will restate the specs for this problem. The transformer is rated at 20kVA, with a primary winding of 7200V and secondary winding of 240V, with leakage reactance of 12%. The load voltage is 235V with a max load of 12kW. Find the voltage supplied by the transformer.

My approach is to find the load current which is the total current at the secondary winding. I then solve for the per unit reactance of the leakage reactance. This impedance is then used to find the voltage drop at the impedance by using the current at the secondary winding. Summing the load voltage and the voltage drop at the impedance is equivalent to the induced voltage at the secondary.

After this, use the turn ratios to solve for the primary induced voltage and were done.

Thank you in advance for helping me out.

7. t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
That's the correct approach. Your solution in post #4 looks reasonable.