# Got Brain Freeze....Need help

Discussion in 'Homework Help' started by Mascha, Jan 26, 2009.

1. ### Mascha Thread Starter New Member

Jan 24, 2009
1
0
From the following info can anyone tell me how to work this out:

A balanced load draws a total power of 90 kw from a 400v three-phase system at unity power factor.
The load is supplied from a 11kv to 400v step-down transformer which has a delta primary & star secondary.
Calculate the line voltage, phase voltage, line current & phase current for both primary & secondary.

Any assistance greatly appreciated.

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Calculate the line current drawn by the load by using this formula:

IL=P/[sqrt(3)*VL*pf]

IL= line current
VL=line voltage
pf=power factor

Thus, you know the line current through the secondary of the transformer. Each secondary winding corresponds to a primary winding and they are related (voltage and current) by the turns ratio. You know the voltage and current on the secondary and thus you can calculate them on the primary by using the turns ratio.

3. ### Skeebopstop Active Member

Jan 9, 2009
358
3
What about phase voltage and current? Would these just be the phasors, and given power factor of one, the same as the line voltage and currents?