Transformer Question

Discussion in 'General Electronics Chat' started by Moriet, Feb 20, 2009.

  1. Moriet

    Thread Starter New Member

    Feb 20, 2009
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    Can someone please help me with a problem that I have?

    If the secondary winding on a transformer is partially shorted across some of the coils would the secondary side's voltage go down and current go up?

    Would the current drop on the secondary since the resistance stayed the same (Not sure if the winding's resistance would be enough to influence this) only the voltage went down?

    Also since power should equal power would this affect anything on the primary side?

    If someone could help me with this I would appreciate it. I am basically trying to figure out what would happen in that situation so if someone could give me a detailed answer I would appreciate it!
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    There would be heat, lots of it, because you have what is effectively a secondary of a center tapped transformer shorted out. I suspect it would be a runaway reaction, the short creating heat, which would ruin even more insulation, creating more shorts.
     
  3. b.shahvir

    Active Member

    Jan 6, 2009
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    :) Secondary voltage will go down since sec. side current will go up. Increased sec. current gives rise to increased voltage drop across secondary winding impedance (or resistance)…. this in turn will cause secondary side voltage to go down.

    Current increases since resistance decreases due to Sec. winding partially short-circuited, hence voltage has to come down as mentioned earlier.

    Power remaining the same, primary current will also increase in a fixed transformation ratio in proportion to compensate for the increased secondary current.

    Also, there would be an electro-thermal runaway as a result of the winding short circuit as mentioned by Bill.
    If you need more details please let me know.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    If it is a voltage transformer then the current through the secondary depends on the load unless the core of the transformer saturates.

    If the secondary partially shorts then the voltage across the load will decrease and thus the current through the load will decrease. Also, the current through the primary will decrease.

    If the secondary output wires are shorted together, a large current will flow through the windings, it will heat, the insulation will melt and the transformer will be destroyed. If there is a protection fuse the fuse will blow and protect the transformer.
     
  5. b.shahvir

    Active Member

    Jan 6, 2009
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    The current thru the sec. load will decrease, no doubt...... but the primary current will increase to compensate for the extra partial short ckt. current which appears in parallel with the load branch.
     
  6. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Thanks for the correction, you are right. It was a clever question.

    Also, the transformer may get hot depending on how many windings were shorted.
     
  7. b.shahvir

    Active Member

    Jan 6, 2009
    444
    0
    I agree completely, it will heat up!
     
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