# Impedance in a Transformer

#### E-student

Joined Apr 9, 2024
2
I'm having trouble finding any information on a question that I am working on please refer to below.
for V2 I calculated 0.33kV using the Peak voltage formula. V2/V1=N2/N1

When V1=6.6kV N1=20 N2=1

I will post the question, but I don't need the question answered as such, because I won't learn anything, I just need some help with formulas to use and definitions.

• For the system indicated overleaf determine the following:
• The voltage V2
• The impedance (The resultant resistance) of the circuit on the V2 side of the circuit
• The current I2
• The true power (or real power) on the low winding side of the transformer kW
• The reactive power kVAR
• The apparent power kVA
• The power factor.
• The Current I1

In the figure, J = Xc is reactance, opposition of capacitor and inductor to sinusoidal current in ohms

#### Ian0

Joined Aug 7, 2020
10,085
Knowing V2, can you now calculate I2 and Z2?
As the transformer is "perfect" you can just replace it and V1 by a voltage source of the same frequency and equal to V1*N2/N1

#### crutschow

Joined Mar 14, 2008
34,718
All those questions can be answered from the fundamental transformer relation for voltage being Vs/Vp = Ns/Np and the current being Is/Ip = Np/Ns.
The primary and secondary currents and impedance follow from those simple relationships.
Thus, for example, for a 2:1 secondary to primary turns ratio, the secondary voltage is twice the primary, and the secondary current is 1/2 the primary (remember that the secondary power must ideally always equal the primary power).

Last edited:

#### E-student

Joined Apr 9, 2024
2
All those questions can be answered from the fundamental transformer relation for voltage being Vs/Vp = Ns/Np and the current being Is/Ip = Np/Ns.
The primary and secondary currents and impedance follow from those simple relationships.
Thus, for example, for a 2:1 secondary to primary turns ratio, the secondary voltage is twice the primary, and the secondary current is 1/2 the primary (remember that the secondary power must ideally always equal the primary power).
so what formula do i use to calc the current either primary or secondary

#### Ian0

Joined Aug 7, 2020
10,085
Kirchhoff tells you that the current in the secondary equals the current in the load.
So the current in the primary is related to the current in the secondary by the turns ratio.

#### crutschow

Joined Mar 14, 2008
34,718
so what formula do i use to calc the current either primary or secondary
The simple equations I posted are sufficient to calculate that.
You just need to think about what is happening in the transformer base on those equations.
Using a formula we give you doesn't help your understanding, which you stated is your goal.

#### MrAl

Joined Jun 17, 2014
11,593
I'm having trouble finding any information on a question that I am working on please refer to below.
for V2 I calculated 0.33kV using the Peak voltage formula. V2/V1=N2/N1

When V1=6.6kV N1=20 N2=1

I will post the question, but I don't need the question answered as such, because I won't learn anything, I just need some help with formulas to use and definitions.

• For the system indicated overleaf determine the following:
• The voltage V2
• The impedance (The resultant resistance) of the circuit on the V2 side of the circuit
• The current I2
• The true power (or real power) on the low winding side of the transformer kW
• The reactive power kVAR
• The apparent power kVA
• The power factor.
• The Current I1

View attachment 319614

In the figure, J = Xc is reactance, opposition of capacitor and inductor to sinusoidal current in ohms
Hi,

Get rid of that inductor first by shorting it or removing it and replacing it with a short (0 Ohms).
Then, figure out how the transformer works by applying a voltage V1 and noting the output voltage is as according to the turns ratio. Then, calculate the current in the resistor R and go from there.
If you want to understand how the impedance reflects to the primary, put a different resistor in series with V1 and short R, then try to solve for that new resistor that gives you the same current in the output winding with R shorted out. Note what the new resistor value comes out to and relate it to the original R and the turns ratio. That will show you how the impedance reflects from one winding to another.

When you include an inductance, you either have to use complex numbers or a ready made formula that is used for reactive loads. I'm not sure what you did in the past so I can't recommend any procedure unless you can tell me that information. There are also simple transformer models you can use to help solve these kinds of problems, but I have to know what you have done in the past first.