I want to ask a question about transformers. Primary and secondary parts are isolated electrically and there is only a magnetic coupling. If there is a short circuit in the secondary part, is our primary current affected by this problem or not? Because there is not any electrical connection.

  • \$\begingroup\$ Of course it does, the coupling works both ways. Where do you think the power in secondary part is coming from? \$\endgroup\$
    – MightyPork
    Feb 4 '15 at 12:19
  • 1
    \$\begingroup\$ The impedance seen by the primary is a transformed version of the impedance in the secondary. If you short the secondary, you're also shorting this transformed impedance. \$\endgroup\$
    – Greg d'Eon
    Feb 4 '15 at 12:25
  • \$\begingroup\$ Why not try it? Do it outside, switch off the primary power if anything 'unusual' happens and keep a CO2/powder fire extinguisher handy. \$\endgroup\$ Feb 4 '15 at 16:39

It's not like a solar panel being shorted i.e. the sun stays the same brightness despite the short. A transformer converts electrical energy to magnetic energy and then back to electrical energy. It does it with pretty good efficiency (90%+ on most transformers). If you short the secondary, the primary takes a lot of current. It's the same with an electric motor - if you lock the armature, you take a lot of current/power/energy.


In a transformer, power is equal on both sides.

When short circuiting the secondary side, with V=IR, the current increases and thus with P=VI, the power increases on the secondary side.

This makes the power increase on the primary side as well. Assuming a constant voltage on the primary side, with P=VI, the current will increase as well, up to the limits of the components.


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