Question

QUESTION

A power transtormer at a receiving substation has the following information on its name plate

Z= (2.5+j10) %;

120 MVA; 330/66 kV; 50 Hz;

ONAF;

Yd1;

A. Explain the meaning of each of the following terms on the name plate of the transtormer.

120 MVA

(1)330/66 kV

(1i)

50 Hz

(IV)

ONAF

Ydi

B. Sketch the phasor diagrams showing the orientation of the voltages on the high-votage side and

the low-voltage side of the transtormer with reference to the clock face; and trom the phasor

dlagrams SKetch thne connection diagrams tor the hign-vOltage side and loW-voltage SIae

respectively.

C.the core losses of the transformer are equal to 0.725 MW, what will be the efficiency of the

transtormer on full-load at a power factor of 0.80 lagging?

D. Calculate the voltage regulation of the transtormer on full-load at a power factor of 0.8 lagging

E.Under what conditions will the transformer's efficiency be maximum? Calculate the maximum

eliciency this transtormer ca operate at.

At what power factor will the voltage regulation be at its lowest? Calculate the voltage regulation

at this power factor.

To accommodate a higher load, a new transtormer rated 150 MVA 330/66 kV, 50 Hz, is to be installed

in parallel with the first transformer.

G. What conditions must be met before two or more transtormers are connected in parallel?

H. Determine the winding resiştance and leakage reactance of the second transtormer in ohms,

referred to the high-voltage side, which will result in the two transformers sharing the load

proportionaly to their apparent power ratings.

1Determine the load on each transtormer it they supPply a total load is 250 MVA at a power factor

of 0.85 lagging