UNIVERSITY OF MAURITIUS
Faculty of Engineering
RESIT EXAMINATIONS
August 2019
PROGRAMME
BEng (Hons) Electrical and Electronic Engineering
BEng (Hons) Electronic and Communication Engineering
MODULE NAME
DATE
Power Systems 1
Wednesday
MODULE CODE
ELEC 2109(3)
07 August 2019
TIME
NO. OF
QUESTIONS SET
09.30 – 12.30 hrs
6
INSTRUCTIONS TO CANDIDATES
Answer ANY FIVE (5) questions.
All questions carry equal marks.
DURATION
NO. OF QUESTIONS
TO BE ATTEMPTED
3 hours
5
POWER SYSTEMS 1 – ELEC 2109(3)
Answer ANY FIVE (5) questions
Question 1 (20 Marks)
(a)
A generating station has a connected load of 450 MW and a maximum demand
of 250 MW. The units generated being 6.15 × 108 kWh per annum. Calculate:
(i)
the demand factor
(ii)
the load factor
[4 marks]
[4 marks]
(b)
The capital cost of a hydro-power station of 100 MW capacity is Rs.1000 per kW.
The annual depreciation charges are 15% of the capital cost. A royalty of Rs.2 per
kW per year and Rs.0.03 per kWh generated is to be paid for using the river
water for generation of power. The maximum demand on the power station is
70 MW and the annual load factor is 60%. Annual cost of salaries, maintenance
charges, etc. is Rs.1,000,000. If 20% of this expense is also chargeable as fixed
charges, calculate the generation cost in two part form.
[12 marks]
Question 2 (20 Marks)
(a)
Derive an expression for the most economical power factor when the kVA
demand is constant.
[10 marks]
(b)
A system is working at its maximum kVA capacity with a lagging power factor
of 0.707. An anticipated increase of load could be met by (i) raising the power
factor of the system to 0.866 by installing power factor correction equipment, or
(ii) installing extra generating plant to meet the increased power demand. If the
total cost of the generating plant is Rs.8,000 per kVA, estimate the limiting cost
per kVAr of the power factor correction equipment which would justify its
installation.
[10 marks]
1
POWER SYSTEMS 1 – ELEC 2109(3)
Question 3 (20 Marks)
(a)
Find the inductive reactance per phase in Ω/m for a three phase line that has
equilaterally spaced conductors of ACSR ‘Dove’. The distance between lines of
various phases is 3.048m and the operating frequency is 60 Hz. From standard
table, Dove GMR = 0.00954024 m, Diameter of Conductor = 0.02354 m.
[10 marks]
(b)
Each conductor of the bundled conductor line shown in Figure 3(b) is ACSR,
’Pheasant’.
Find the capacitive reactance to neutral of the line in
ohm/km/phase. From standard table, GMR=0.014204 m, outside diameter of
each conductor is 0.0351028 m and system frequency=60 Hz.
[10 marks]
0.45 m
a
a'
b'
b
8m
8m
c'
c
Figure Qu. 3(b)
Question 4
A 3-phase, 50 Hz overhead transmission line 100 km long has the following constants:
Resistance/km/phase = 0.1 Ω
Inductive reactance/km/phase = 0.2 Ω
Capacitive susceptance/km/phase = 0:04 x 10-4 S
Determine
(i)
the sending end current
[5 marks]
(ii)
sending end voltage
(iii)
sending end power factor and
[5 marks]
[5 marks]
(iv)
transmission efficiency
[5 marks]
when supplying a balanced load of 10,000 kW at 66 kV, pf. 0.8 lagging. Use nominal T
method.
2
POWER SYSTEMS 1 – ELEC 2109(3)
Question 5 (20 Marks)
A 30 MVA, 11 kV generator has Z+ = Z- = j0.2 pu, Z0 = j0.05 pu. A line to ground fault
occurs on the generator terminals. Find the fault current and line to line voltages
during fault conditions. Assume that the generator neutral is solidly grounded and that
the generator is operating at no load and at rated voltage at the occurrence of the fault.
Question 6 (20 Marks)
(a)
(b)
(c)
(d)
With the help of a diagram, explain the operation of a vacuum circuit breaker.
[6 marks]
List four advantages and four disadvantages of air blast circuit breakers.
[4 marks]
With the help of a diagram, explain the operating principle of a differential relay.
[5 marks]
List the five classes of protective relays based on their logical functions.
[5 marks]
____________________________________________________________
END OF QUESTION PAPER
3