- #1

- 6

- 1

- Homework Statement
- A 415V to 11 kV transformer has a rating of 200 kVA. The winding resistance

and leakage reactance when referred to the primary are 0.014 Ω and 0.057 Ω

respectively.

(a) Determine the % regulation of the transformer at 0.8 power factor lagging.

(b) In designing a particular 415V to 11 kV, 200 kVA transformer, the primary

winding resistance is to be 10 mΩ. Find the maximum winding resistance of the

secondary winding if the transformer is to have 2% regulation at unity power

factor.

- Relevant Equations
- %Reg = 100% * (I(R * cosθ ± X * sinθ))/E

So I've done part a)

Primary current = 200000/415=481.9

Cos θ = -0.8

Sin θ = 0.6

Reg=(481.9 ( 0.014*-0.8 + 0.057*0.6))/415

= 0.0267

Reg% = 2.67%

Part b I simply used the same equation but for secondary:

@ unity p.f., cos θ =1, sin θ = 0

secondary current = 200000/11000 = 18.18

18.18(R*cosθ)/11000=0.02

solved for R gives R=12.1Ω

However, this hasn't utilised the 10mΩ given in the question so I assume it can't be as simple as that. I've seen a couple of threads with this question in from a few years ago but the explanations just didn't make sense to me

Primary current = 200000/415=481.9

Cos θ = -0.8

Sin θ = 0.6

Reg=(481.9 ( 0.014*-0.8 + 0.057*0.6))/415

= 0.0267

Reg% = 2.67%

Part b I simply used the same equation but for secondary:

@ unity p.f., cos θ =1, sin θ = 0

secondary current = 200000/11000 = 18.18

18.18(R*cosθ)/11000=0.02

solved for R gives R=12.1Ω

However, this hasn't utilised the 10mΩ given in the question so I assume it can't be as simple as that. I've seen a couple of threads with this question in from a few years ago but the explanations just didn't make sense to me