Question about Medium Voltage Power Transmission

Thread Starter


Joined May 18, 2018
The High Voltage from the supply side is 22kV. It goes through a three-phase distribution transformer of 1000kVA. What can be said/calculated about the load that the transformer is supplying? What are the possible values of V1, V2, V3 and I1, I2, I3 on the high voltage side and secondary side respectively?
The three-phase voltage used here is 400V and the frequency is 50Hz
Note: No exact values are required. I am just trying to understand some basic concepts. Thank you.


Joined Oct 2, 2009
Welcome to AAC!

This sounds like Homework question to me. I know nothing about power transmission systems.

However, how many ways can you combine 400V three-phase voltage?
Given that the power rating of the transformer is 1000kVA, current = power / voltage.
How does the phase difference affect the current, voltage, and VA power calculation?


Joined Nov 18, 2016
First, I am tired of hearing this: "The three-phase voltage used here is 400V" !!!

This is an AC circuit which is completely different from a DC circuit.
You need to answer these questions to understand this standard last level transformer to house line.

1. Is the 400 volts, line or phase voltage? What is line and phase voltage?

2. How do transformers lower and make higher the voltage?

3. What is 3 phase and 1 phase voltage?

4. Is the motor powered by 3 phases or 1 phase.

5. What is effective and maximum value of voltage or current and why is it used?
it also seems like an assignment to me. what i should advice you to check and understand are basic concepts like line-to-line voltages an currents, line-to-phase voltages. try to identify what v1,v2,an v3 represent in the line an the required calculations involved.


Joined Jan 23, 2018
Normally, when we say "3 phase 480 volts, we mean line to line, delta connected. BUT NEVER!!! automaticly assume that anybody from outside that discussion means the same thing. SO, when asking a question always specify wye or delta and are you giving phase to phase voltage or phase to neutral voltage. Also, beware, because in some places one phase of the delta connection is grounded. THAT can cause problems for the unwary, big time.