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Numbskull
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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 ##\Omega## and 0.057 ##\Omega## 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 m##\Omega##. Find the maximum winding resistance of the secondary winding if the transformer is to have 2% regulation at unity power factor.
Homework Equations
% Regulation = ## \frac {{VA}_{rating}} {V_1^2} ## x (R’p cos ##\theta## + X’p sin ##\theta##) x 100%
The Attempt at a Solution
(a)
##\frac {200 \times 10^3}{(415)^2}## x ((0.014 ##\times## 0.8) + (0.057 ##\times## ##\sqrt{1 - 0.8^2}))## x 100% = 5.272% regulation
(b)
Voltage regulation (%) ## \approx \frac {200 \times 10^3}{(415)^2} ## x R'p x 100%
Rearranging to make R'p the subject, I get 17.2225 m##\Omega## (as the primary reflected impedance), and this is only an approximation according to the formula provided in the textbook.
Trying to analyse this part in my head, I think that I need to get that primary impedance down to 10m##\Omega##. This means that I need to alter (calculate) the maximum current / voltage on the secondary side taking the 2% voltage drop, leakage reactance and 200kVA max power into consideration?
I'm keen to learn this as per the forum principles, but some gentle guidance would be welcome