QUESTION 1. [50 Marks]
A 3.3 kV, 50 Hz system supplies three 415V, 50 Hz balanced loads via an ideal Yy0 three phase transformer as shown as a single line diagram in Figure 1 below.

Screenshot from 2018-09-27 15-12-09

The three loads are as follows:
LOAD 1 (STAR): 35 kW at a power factor of 0.6 lagging;
LOAD 2 (DELTA): R = 22 Ω in series with C = 270 μF;
LOAD 3 (DELTA): 22 kVA at a power factor of 0.75 lagging
(i) the Power (kW), Reactive Power (kVAr) and Apparent Power (kVA) of the Delta connected Load 2;   [ 14 Marks]
(ii) the Total Power and Power Factor supplied from the 3.3kV system before Power Factor correction;   [ 14 Marks]
(iii) the Capacitance Reactive Power (kVAr) per phase required to correct the overall system power Factor to 0.87 lagging;   [ 12 Marks]
(iv) the three phase transformer primary phase current before and after Power Factor Correction.   [ 10 Marks]

QUESTION 2. [50 Marks]
A 135 kVA, 50 Hz transformer with a 440 V primary and a 6600 V secondary has a Secondary Output Voltage V 2 = 6600 V, when the secondary Load Impedance of: Z L = 267.8 + j180 Ω

Screenshot from 2018-09-27 15-12-54

For Transformer determine:
(i) The approximate equivalent circuit model with the parameters referred to the primary shown on the model;  [ 12 Marks]
(ii) The secondary Load Current I L & Power Factor PF L ;   [ 6 Marks]
(iii) The Voltage Regulation with the above secondary Load.    [ 6 Marks]
(iv) The input Supply Current I 1 & Power Factor PF 1 ;   [ 18 Marks]
(v) The efficiency of the transformer with the above secondary Load;    [ 8 Marks]

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