# Single Phase Transformer

1. Apr 3, 2011

### dvep

1. The problem statement, all variables and given/known data

Figure 1 shows the equivalent circuit of a single phase transformer and figure 2 shows the approximate equivalent circuit.

Reduce the circuit to approximate form and find:
rm, xm, R1, X1

Using the approximate equivalent circuit calculate-

With the transformer operating at no-load:

primary current , primary power factor, primary real power, secondary voltage.

I am given in the equivalent circuit:
r1, r2, rm, x1,x2,xm, turns ratio, V1

2. Relevant equations

R1 = r1' + r2'
X1 = x1 + x2' = x1 +x2(N2/N1)

3. The attempt at a solution

Using the equations above I have found R1 and X1
I now need to find rm and xm of the approximate equivalent circuit and primary current , primary power factor, primary real power, secondary voltage.

I am struggling with this, any help would be appreciated, thankyou.

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Last edited: Apr 3, 2011
2. Apr 7, 2011

### Samtheguy

To my knowledge, rm and xm do not change when converting to the approximate equivalent circuit.
To go about finding the primary current (Io) you will have to calculate the currents Ioa (active component) and Ior (reactive component). The formulae for finding these are:
Ioa = V1 / rm
Ior = V1 / xm
Then, to find Ioa, use the formula: Io = √((Ioa)^2 + (Ior)^2)
The primary power factor is found using: Ioa / Io
Primary real power is found by: Poc (which means Open circuit power) = (V1)^2 / rm
The secondary voltage is calculated using: V2 = V1 x N2/N1

Hope this helps.

3. Apr 11, 2011

### dvep

Now with a load impedance I now need to calculate:

primary current, secondary current, secondary apparent power, secondary reactive power, the effiency, primary power factor, secondary voltage, secondary real power, secondary power factor, and voltage regulation.

I have referred the load impedance to the primary and calculated ZL', I added this impedance to R1 and X1.
So I am now left with three impedances, I took the reciprocals of these and added them together, then took the reciprocal of this again, and this gives me the input impedance.

So to calculate the primary current I used V1/ZL, however it gives me a very big number, is this the correct method?

4. Apr 21, 2011

### Chalex4

I'm interested in knowing if anyone else can confirm this statement? I have a very similar problem to yours that I need to solve.