transformer secondary voltage question

[teepee]

Hello,

If I got a mains transformer with dual secondary windings how can I get a constant uninterruptible voltage from the other winding even if the other winding is shorted?

Does both secondaries go to 0 volts if one of them is shorted (both have same number of turns)? If they do how can I overcome this problem?

-k

 

[A.Anand Srinivasan]

no both of the secondaries wont go to zero volt.... since it is shorted the voltage across that coil becomes zero (very small voltages result but they r dissipated by the resistance in the wire).... the shorting of one coil doesn't affect the other coil and hence you can expect constant uninterrupted supply from it....

 

[Kral]

teepee,
Shorting one secondary produces a load on the primary. This load is approximately equal to the following:
. (2PifXl + Rdc) (N^2)
. where Xl is the leakage inductance of the shorted secondary
. Rds is the DC resistance of the shorted secondary.
. N is the turns ratio of the primary wrt the shorted secondary
. f is the frequency
This load will cause a voltage drop across the primary which will cause the voltage on the unshorted secondary to drop. However, the voltage won't go to zero until the transformer burns up
Regards,
Kral

 

[dfullmer]

Yeah, he's right ...what Kral said:|


Regards

dfullmer

 

[nguyennam]

What happens depending how much your transformer's power is.

In case of low power transformer, where the resistance of the winding is rather high, even shorted secondary winding doesn't make the transformer burned out. So in this case, the 2nd secondary winding voltage would be low, but not zero.

In case of high power transformer, where the resistance of the winding is rather low, so shorting the secondary winding may quickly make transformer burnt out. While shorting circuit, the magnetic core becomes saturated, the current in primary winding increases suddently, very little power will be transferred to the secondary winding and its voltage will be dropped down to almost zero.

You should make some experiments and you will understand.

nguyennam

 

[AndrzejM]

First you should define more precisely what kind of the secondary short circuit you have in mind.
1. Is it a situation when the transformer output terminals are shorted
or
2. The short circuit appears inside transformer (because the coil isolation breaks).

In the second case you can do nothing.

In the first case you can protect one voltage by using resistors in series with the secondary to limit the short circuit current and optionally a fuse (it is worthy to consider a polymer self recovery type). Also the transformer should be oversized (by power and output voltage) because of the power loses and voltage drop in series resistors.

In case of short circuit in one winding a small voltage drop down appear on the second winding and the voltage will go to be higher from the moment the fuse protecting the first winding will do the job.