Electrical Supply and Distribution Systems

Job Title: Electrical Supply and Distribution Systems
Job Category: Academic
Word Count: 1200
Job Price: 18
Deadline: 2018/02/17 12:00
Job Description: 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.
2. (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.
(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.
3.  From the operating chart shown in FIGURE 15 of lesson ESD – 2 – 2,
determine the following performance limitations for a generator:
(a) where the power limit and the MVA limit coincide;
(i) the power factor
(ii) the load angle
(iii) the MVAr output
(b) where the power limit and the stability margin coincide;
(i) the p.u. excitation
(ii) the MVA output.
4.  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

Quantity Value
Synchronised Reactance 2.0. p.u.
Excitation Limit 2.8 p.u.
Maximum Margin 570 MVA
Turbine Power Limit 500 MW
Stability Margin 10% Full Load Power