Question 1. For a Yd1 transformer:
(a) draw the connection diagram
(b) show how the connections must be modified to allow parallel operation with a Yd11 transformer
(c) draw a phasor diagram for the modified connection.

Question 2. In your own words, state the three essential and two highly desirable conditions which must be fulfilled for two 3-phase transformers to operate satisfactorily in parallel.

State briefly what you think may be the possible consequences of not complying with these conditions.

Question 3. (a) Two single-phase transformers have the following impedances referred to the secondary side.
Unit A rated 250 kVA (0.09 + j2.7) Ω Unit B rated 400 kVA (0.04 + j1.6) Ω

Determine the load taken by each machine as a percentage of its rating when they share a common load of 500 kVA at 0.73 p.f. lag.

Question (b) Transformer A is rated at 300 kVA with an impedance of (0.09 + j0.18) Ω
Transformer B is rated at 200 kVA with an impedance of (0.09 + j0.23) Ω

If these transformers are connected in parallel to supply a common load, determine the percentage overload on B when A supplies its full load at p.f. 0.45 lag.

Question 4. From the operating chart shown determine the following performance limitations for a generator:

1. (a) where the power limit and the MVA limit coincide;
1. (i) the power factor
2. (ii) the load angle
3. (iii) theMVAr output

2. (b) where the power limit and the stability margin coincide;
1. (i) thep.u. excitation
2. (ii) the MVA output.

Question 5. A 3-phase synchronous generator rated at 570 MVA is connected to an infinite busbar.

Using the data given in the table below, plot the capacity chart of the generator.