Dumb question regarding short circuit test equivalent resistance

In summary, the transformer short circuit test is used to find Req by shorting the secondary and measuring the power and current. The formula for Req is Rpri + Rsec*(Npri/Nsec)^2, where N is the number of turns. This allows us to find the reflected secondary resistance. We can also use this test to find the primary and secondary resistances by measuring with a multimeter. However, we still need either the primary or secondary coil resistance to accurately know all parameters of the transformer.
  • #1
tim9000
867
17
Hi,
Silly little question about the transformer short circuit test.
When I perform it with the secondary shorted and I get Req = Power / current2

is this Req = Rpri + Rsec?
If I measured Rpri and Rsec with a multimeter?

Thanks
 
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  • #2
tim9000 said:
is this Req = Rpri + Rsec?
It is Rpri+Rsec*(Npri/Nsec)2.
The second term on the RHS is the reflected secondary resistance or the secondary resistance "seen" by primary.
 
  • #3
cnh1995 said:
It is Rpri+Rsec*(Npri/Nsec)2.
The second term on the RHS is the reflected secondary resistance or the secondary resistance "seen" by primary.
Can we move this a = (Npri/Nsec)2 term to get the primary and secondary resistances as seen by themselves?
So if I measure Rpri and Rsec with a multi meter then will the value of Rpri I get on the meter be
Rpri = Req - Rsec*(Npri/Nsec)2

Where Rsec is the value of the secondary from the meter?
 
  • #4
tim9000 said:
Can we move this a = (Npri/Nsec)2 term to get the primary and secondary resistances as seen by themselves?
So if I measure Rpri and Rsec with a multi meter then will the value of Rpri I get on the meter be
Rpri = Req - Rsec*(Npri/Nsec)2

Where Rsec is the value of the secondary from the meter?
Yes (provided the test is performed with secondary shorted).
 
  • #5
cnh1995 said:
Yes (provided the test is performed with secondary shorted).
Just to be 100% clear: When you say the test I presume you mean the Short Circuit test in finding Req, and not measuring the coils resistance with the multimeter? (because I can't see how it would make any difference to that)
So bottom line is that other than the values I can derive from Short Circuit and Open Circuit tests, I still need either the Primary coil resistance, or the Secondary coil resistance (via multimeter) to accurately and specifically know every individual parameter of the transformer? (i.e. to separate the primary and secondary resistance values out from Req)
Thanks again
 
  • #6
tim9000 said:
Just to be 100% clear: When you say the test I presume you mean the Short Circuit test in finding Req, and not measuring the coils resistance with the multimeter? (because I can't see how it would make any difference to that)
So bottom line is that other than the values I can derive from Short Circuit and Open Circuit tests, I still need either the Primary coil resistance, or the Secondary coil resistance (via multimeter) to accurately and specifically know every individual parameter of the transformer? (i.e. to separate the primary and secondary resistance values out from Req)
Thanks again
Yes to all.
 
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Likes tim9000
  • #7
cnh1995 said:
Yes to all.
Thank you
 

FAQ: Dumb question regarding short circuit test equivalent resistance

What is the purpose of a short circuit test for equivalent resistance?

The short circuit test for equivalent resistance is used to determine the resistance of a circuit when a short circuit is present. This can help in analyzing the overall stability and efficiency of the circuit.

How is the equivalent resistance calculated in a short circuit test?

In a short circuit test, the equivalent resistance is calculated by measuring the voltage and current in the circuit when a short circuit is present. The equivalent resistance is then calculated using Ohm's law (R=V/I).

Can the equivalent resistance be different in a short circuit test compared to a normal circuit?

Yes, the equivalent resistance can be different in a short circuit test compared to a normal circuit. This is because a short circuit causes a significant increase in current, which can lead to changes in the overall resistance of the circuit.

What factors can affect the equivalent resistance in a short circuit test?

Some of the factors that can affect the equivalent resistance in a short circuit test include the type and quality of the components used in the circuit, the length and thickness of the wires, and the temperature of the circuit.

How can the results of a short circuit test be used in circuit analysis?

The results of a short circuit test can be used to determine the overall stability and efficiency of the circuit. They can also be used to identify any potential issues or faults in the circuit that may need to be addressed. Additionally, the equivalent resistance can be used in further calculations and analysis of the circuit.

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