Transformer Short Circuit Test
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- Опубликовано: 5 фев 2025
- In this video i discuss finding the impedance voltage on a transformer using a short circuit test for academic purposes. This video is intended to supplement lecture material delivered in class, but please feel free to ask questions in the comments below.
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I'm happy it was helpful. Thanks for watching and commenting.
what is the rated current of each phase on a 3 phase transformer? what are the methods to use if u have only single phase variac and you want to test 3 phase transformer?
Will will be the %impedance of the same rating in bank configuration (3-1phase)?
Thanks for a clear explanation on how we find impedance percentage. Why is it important to have impedance percentage on the transformer name plate? I'm having trouble finding a clear answer. I would appreciate any help.
The most important reason is that it is used in the formula to determine available fault currents in the system in the event of a short circuit so we can properly size the interrupting ratings of our overcurrent devices.
Also can determine voltage drop in transformer at given load. Troubleshooting low voltage complaints.
insight giver🙂🙂
Thank you very good video!!
Happy it helped. Thanks for watching and commenting!
Dear Schulerruler, please clear my confusion: if I have a 240VAC supply, if I connect the Live and Neutral wires with a copper cable, that is very DANGEROUS, it is a Short Circuit! With very small resistance between L and N, a very large current flows in the circuit , within fraction of second, the main circuit breaker would trip to prevent the cable from catching fire!!!!
BUT if I connect the L& N wire from the above supply to a transformer, (ie the primary of the transformer , which is essentially coil of pure copper wire with very low resistance) , it is OK, no tripping at the main circuit board - meaning: the primary coil is NOT short circuited.
Question: why is that so? please explain. TQ so much.
We will start with the question about the primary. When you connect a supply to a coil, the reason it does not short is because of the amount of inductive reactance that the coil has due to the changing frequency of the AC supply. If you connected the coil in DC, however it would be a MASSIVE amount of current as there is no changing frequency that causes the opposition in the circuit. It would only be the resistance of the physical copper at that point which is not much.
The secondary is ONLY short circuited when performing a short circuit test. The primary would have a variable voltage applied starting at zero, and SLOWLY increase to an account that causes rated secondary current to flow when secondary is short circuited. As you have pointed out, the secondary would have very little impedance in a short circuit condition, so it would not take a lot of primary voltage to cause rated current to flow.
You helped me understand...you're good
Why do we wanna hit the secondary current and not the primary current?
Because of mutual induction
You would be increasing the voltage on the HV side to possible hazardous voltages. When the ratio of transformer is close 2 to1 or 3 to 1 it wouldn’t matter . When you get to higher ratios like 50:1 for example 12,000v / 240v with a 5% impedance your amp clamp would see 2.08 amps and voltage in that closed loop would be 600v. While you would apply only 12v of the 120v max of your supply voltage. If you didn’t control that and you accidentally were set full 120v you would have 6000v on HV side. Applying full voltage by accident in reverse hookup your voltage on HV would be 120v and voltage on LV would be 2.4v.
Thaanku so much