Power System Analysis and Design (MindTap Course List)
6th Edition
ISBN: 9781305632134
Author: J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma
Publisher: Cengage Learning
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Chapter 9, Problem 9.13P
Consider the oneline diagram of a simple power system shown in Figure 9.20. System data in per-unit on a 100-MVA base are given as follows:
The neutral of each generator is grounded through a current-limiting reactor of 0.08333 per unit on a 100-MVA base. All transformer neutrals are solidly grounded. The generators are operating no-load at their rated voltages and rated frequency with their ENIFs in phase. Determine the fault current for a balanced three-phase fault at bus 3 through a fault impedance
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Q2. The single-line diagram of a simple three-bus power system
is shown in Figure-2. Each generator is represented by an emf
behind the sub-transient reactance. All impedances are
expressed in per unit on a common MVA base. All resistances
and shunt capacitances are neglected. The generators are
operating on no load at their rated voltage with their emfs in
phase. A three-phase fault occurs at bus 3 through a fault
impedance of Zf = j0.19 per unit.
(i) Using Th'evenin's theorem, obtain the impedance to the
point of fault and the fault current in
(ii) Determine the bus voltages
per
unit.
) j0.05
j0.075
j0.75
2
j0.30
j0.45
Figure-2: Single line diagram of the
power system network for Q2
3
Consider the three single-phase two-winding transformers shown in Figure. 3. The
high-voltage windings are connected in Y.
(a) For the low-voltage side, connect the windings in A, and label the terminals a,
b, and c in accordance with the American standard.
(b) Relabel the terminals a', b', and c' such that VAN is 90° out of phase with V₂'b'
for positive sequence.
DI
H₂
Figure. 3: Three-Winding Transformer
Three zones of a single-phase circuit are identified in the figure. The zones are connected by
transformers T₁ and T2, whose ratings are also shown. Using base values of 100 kVA and 240 volts in
zone 1, draw the per-unit circuit and determine the per-unit impedances and the per-unit source
voltage. Then calculate the load current both in per-unit and in amperes. Transformer winding
resistances and shunt admittance branches are neglected.
Zone 1
Zone 2
Vs = 220/0° volts
3---38
T,
30 KVA
240/480 volts
M 0.10 p.u.
Xoa
Xune = 2 fl
T
T₂
20 kVA
460/115 volts
Xeg = 0.10 p.u.
Zone 3
ww
Zload = 0.9 - 10.20
Chapter 9 Solutions
Power System Analysis and Design (MindTap Course List)
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