Transformer short circuit secondary

[Jk1996]

Hi I’m trying to understand the physics of a transformer with the secondary short circuited. When it’s shorted I’ve read something about the current decreasing in the secondary and rising in the primary what causes this?

 

[Gr8blu]

Jk1996: A transformer is one type of electric machine. All transformers are used to change energy from one type to another. The input (primary) is electrical energy in the form of current, which passes through a multi-turn conductor to create a magnetic field. The magnetic field then transfers the energy to the output (secondary) winding, which also has a multi-turn conductor. The magnetic field interacting with the secondary conductor produces an output energy in the form of electrical current. The amount of output current is related to the input current by the ratio of turns on each side. Since the "strength" of the magnetic filed remains constant, (AMP 1 * TURN 1) = (AMP 2 * TURN 2).

Another way to look at this is that the impedance of the conductor on each side is a combination of resistance (R) and inductance (L). Both are related to the length of the conductor, which is proportional to the number of turns. So instead of using "Turn 1" and "Turn 2" in the equation above, we could use (Amp 1)*(R1 + j*w*L1) = (Amp 2)*(R2 + j*w*L2). When we short the secondary ("2") side, the secondary impedance looks really low ... which means the secondary current gets really high (e.g., short-circuit current). On the primary ("1") side, the REFLECTED impedance looks huge ... which, when coupled with the high secondary current, causes the primary side current to increase. Note that the REFLECTED impedance is the impedance of the secondary seen from the primary side of the air gap.

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