CONFIDENTIAL
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
TEST 1
(ONLINE ASSESSMENT)
SEMESTER II
SESSION 2020/2021
COURSE NAME : INDUSTRIAL POWER SYSTEMS
COURSE CODE : MEK 10203
PROGRAMME CODE : MEE
EXAMINATION DATE : 27th APRIL 2021
DURATION : 2 HOURS
INSTRUCTION : ANSWER ALL QUESTIONS
THIS QUESTION PAPER CONSISTS OF FIVE (5) PAGES
CONFIDENTIAL
CONFIDENTIAL MEK 10203
Q1 (a) A new factory is planning to get electricity supply from the local utility company. The
proper supply voltage for this factory is supposedly 33 kV. Unfortunately, due to
incorrect maximum demand estimation by the appointed electrical consultant, the
installed supply voltage is 11 kV. Discuss two (2) main consequences of this problem.
(4 marks)
(b) A distribution transformer (Tx) is to be installed in a factory to serve the loadings as
depicted in Figure Q1(b). The transformer will be connected to the grid system.
(i) Decide the initial transformer sizing based on maximum demand criteria. The initial
decision made should be based on the requirements as given in Appendix. The
sizing should be stated the primary kV/ secondary kV, standard kVA rating and
impedance % (minimum % should be considered at this stage).
(7 marks)
(ii) Investigate the voltage variation (in percentage) during the motor starting.
(3 marks)
(iii) Recommend the proper impedance % of the transformer if the voltage variation
during the motor starting is to be limited to a maximum value of 8%.
(3 marks)
(iv) If the annual growth rate of the load demand is taken as 2%, analyse the maximum
period (in year) that the standard kVA as selected in Q1(b)(i) is valid based on the
maximum demand criteria.
(3 marks)
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Q2 (a) A new glue manufacturer is decided to have an adhesive mixer machine. Describe in
brief the suitable motor for this application with appropriate justification. Sketch the
torque-speed characteristics curve for this load.
(5 marks)
(b) A 440 V, two-pole, 50 Hz, Y-connected induction motor is used as a pump in an
industrial plant. It has an inductive reactance of 3 Ω and a stator resistance of 0.4 Ω. The
rotor resistance referred to the stator is 0.25 Ω. The motor is driving a constant-torque
load of 80 Nm at operating slip of 3.25%. The braking system of this motor is utilising
the Fixed Width Modulation based dynamic braking technique. The duty ratio is taken
as 20%. The motor is driven by a six-step converter with DC link voltage of 250 VDC.
(i) If the motor speed is controlled via frequency, point out the motor current at rated
frequency and at the maximum frequency.
(6 marks)
(ii) Analyse the motor speed at rated frequency and at the maximum frequency for the
case in Q2(b)(i).
(2 marks)
(iii) Determine the braking current required for this motor.
(2 marks)
(iv) Analyse the starting current of this motor at rated frequency and at the maximum
frequency.
(2 marks)
(v) Propose a better method so that the starting current is remained at minimum value.
Demonstrate the method.
(3 marks)
– END OF QUESTIONS –
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CONFIDENTIAL MEK 10203
TEST 1
SEMESTER/SESSION : II/ 2020/ 2021 PROGRAMME CODE : MEE
COURSE NAME : INDUSTRIAL POWER SYSTEMS COURSE CODE : MEK 10203
Grid system
Tx
Lump Load, L1 Lump Load, L3
650 kW + 820 kVAr 950 kVAr
PF = 0.76 lagging
M
Lump Load, L2
500 kW 1250 hp
PF = 0.82 lagging Starting current = 6.5 X
PF = 0.85 lagging,
Efficiency = 96%
Figure Q1(b)
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CONFIDENTIAL MEK 10203
TEST 1
SEMESTER/SESSION : II/ 2020/ 2021 PROGRAMME CODE : MEE
COURSE NAME : INDUSTRIAL POWER SYSTEMS COURSE CODE : MEK 10203
Appendix A
Table A1
Supply
M.D ranges of individual consumer Minimum supply scheme
voltage
Up to 12 kVA 230 V Single phase overhead or underground services from existing LV network.
Three phase overhead or underground cable service from existing LV
> 12 kVA to 100 kVA (Non Domestic) 400 V
network subject to system availability study by TNB.
Three phase overhead or underground cable service from existing LV
Up to 100 kVA (Domestic) 400 V
network subject to system capability study by TNB.
Underground cable service from feeder pillar or a new/ existing substation,
> 100 kVA to 350 kVA 400 V
subject to system availability study by TNB.
> 350 kVA to < 1000 kVA 400 V Direct underground cable service from new substation.
Directly fed through TNB 11 kV switching station. An additional PPU
1,000 kVA up to < 5,000 kVA 11 kV
land may need to be allocated subject to system capability study by TNB.
Directly fed through TNB 22 kV switching station. An additional PPU
1,000 kVA up to 10,000 kVA 22 kV
land may need to be allocated subject to system capability study by TNB.
Directly fed through TNB 33 kV switching station. An additional PMU
5,000 kVA to 25,000 kVA 33 kV
land may need to be allocated subject to system capability study by TNB.
Directly fed through TNB 132 kV or 275 kV substation respectively. TNB
132 kV, shall reserve the absolute right to provide alternative arrangements after
25,000 kVA to < 100,000 kVA
275 kV taking into consideration the location, economic and system security
factor.
Directly fed through TNB 275 kV substation. TNB shall reserve the
100,000 kVA and above 275 kV absolute right to provide alternative arrangements after taking into
consideration the location, economic and system security factor
Table A2
Secondary Impedance range
Primary (kV) Rating (kVA) Construction Type
(kV) (%)
380 – 440 150, 250, 300, 400, 500, 630, 750, 1,000, 1,250, Oil-filled and Dry-
3 – 33 3–7
V 1,600, 2,000, 2,500 type
10 – 12 3 – 7.2 4,000, 5,000, 6,300, 7,500, 10,000 Oil-filled 5 – 10
20 – 24 3 – 12 4,000, 5,000, 6,300, 7,500, 10,000 Oil-filled 5 – 10
33 – 36 3 – 12 4,000, 5,000, 6,300, 7,500, 10,000 Oil-filled 5 – 10
66 3 – 36 4,000, 5,000, 6,300, 7,500, 10,000, 16,000 Oil-filled 5 – 15
4,000, 5,000, 6,300, 7,500, 10,000, 16,000, 25,000,
132 3 – 110 Oil-filled 5 – 20
40,000, 50,000
10 – 33 3 – 11 4,000, 5,000, 6,300, 7,500, 10,000, 16,000, 20,000 Dry-type 5 – 10
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