Determining voltage in transformers

[SGL18]

I don't even know where to start! anyone got any ideas?

A transformer having a 2:1 turns ratio is considered to have a primary resistance and reactance of 1ohm and 2ohm respectively, and a secondary resistance and inductance of 1ohm and 6.37mH respectively. Magnetising current for this transformer is negligible. A 50Hz supply is connected such that a primary current of 10A flows when a load of 60ohm is connected. Determine the primary referred total winding resistance and reactance, and the load and supply voltages. (Hint: Remember that the voltage angles will depend on what you take as your reference.) Determine the magnitude of the supply voltage required to establish the same load voltage if the transformer were regarded as ideal, and thereby determine the percentage increase in voltage supplied to account for the transformer losses.
[5ohm; 10ohm; 1.2kV/angle 0; 2.452kV /angle 2.34; 2.4kV; 2.2%]

 

[tiny-tim]

Hello again SGL18!

(have an ohm: Ω )

I don't even know where to start! anyone got any ideas?

Start questions like this by by drawing a diagram, and then writing out the given facts in equation form …

show us what you get. ​

 

[SGL18]

hey tiny tim! This is the problem sketched out, i think its correct!
sorry for my poor drawing skills!

 

[tiny-tim]

ok, now write out all the equations you can think of (particularly involving impedance voltage and current)

 

[SGL18]

V=IR I =V/R R=V/I P=VI ω=2∏f P=I²R P=V²/R

any of these?

 

[tiny-tim]

I meant equations using the actual values given in the question.

 

[SGL18]

This is what I have been able to work out so far, I think it's correct:

Impedance for primary side: Z = R+jX so Z = 1+j2 which in polar form gives 2.2/_63.4

Impedance for secondary side: Z = R+XL so XL = ωL = 2∏ x 50 x (6.37x10ˆ-3) = 2
so 2/_90 or in polar form 0+j2 than added this to the resistance gives 1+j2

Current for primary side:
V=IZ so V=10/_0 x 2.2/_63.4 = 22V

 

[gneill]

This is what I have been able to work out so far, I think it's correct:

Unfortunately, it doesn't agree with the given answers.

You're missing some fundamental concepts that relate to transformers. Such as how impedances from one side 'transform' to the other, how voltages and currents relate on either side, and so on.

 

[SGL18]

the question asks for the primary winding resistance and reactance, that's what I'm unsure how to solve, what i have done is just added the resistances and reactances given

 

[gneill]

the question asks for the primary winding resistance and reactance, that's what I'm unsure how to solve, what i have done is just added the resistances and reactances given

Not quite. The question asks for the "primary referred total winding resistance and reactance", which is not the same thing. The impedances in the secondary circuit will have a 'reflection' back to the primary. This comes about because of the way that the primary and secondary voltages and currents are interrelated. You should check your notes and text for this.

 

[tiny-tim]

SGL18, you don't seem to be using V₁/V₂ or I₁/I₂.

 

[SGL18]

Alright i'll give that a shot!

cheers :)