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Course : ET601-Power System Protection Lecturer : En. Muhd Halalluddin Abd. Rahim
Programme : DET 6 A/B/C/D/E Total marks : 20 marks
Assessment task : End of Chapter Duration :
Name : _______________________
Registration No : _______________________
TITLE : Fault Current and MVA Calculation Method
OUTCOMES : CLO1, LD1
Upon completion of this course, students should be able to:
i. Explain clearly the basic principle of various protection equipment used for
electrical protection scheme. (C2)
1. Define the meaning of per unit system. (CLO1:C1)
[3 marks]
2. Explain the advantages of using per unit in power system. (CLO1:C2)
[3 marks]
3. Calculate the Z p.u if S base = 15 kVA, I base = 1200 A and Z actual = 10 (CLO1:C3)
[3 marks]
4. Four sets of 12 kV generator were connected in parallel to a bus-bar having a rating of
25MVA, 0.07 p.u, 65MVA, 0.13 p.u, 48MVA, 0.32 p.u and 27MVA, 0.15 p.u
respectively. If fault occur at the bus bar (between G1 and G2), and by using 55MVA as a
base value, calculate:
i. The short circuit apparent power, Ssc
ii. The short circuit current, Isc (CLO1:C3)
[11 marks]
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Course : ET601-Power System Protection Lecturer : En. Muhd Halalluddin Abd. Rahim
Programme : DET 6 A/B/C/D/E Total marks : 20 marks
Assessment task : End of Chapter Duration :
Name : _______________________
Registration No : _______________________
TITLE : Fault Current and MVA Calculation Method
OUTCOMES : CLO1, LD1
Upon completion of this course, students should be able to:
i. Explain clearly the basic principle of various protection equipment used for electrical
protection scheme. (C2)
1. Define the meaning of per unit system. (CLO1:C1)
The per unit system is used to express values of voltages, currents, powers, and
impedances of various power equipment. It is mainly used for transformers and AC
machines. For a given quantity (voltage, current, power, impedance, torque, etc.) the per
unit value is the value related to a base quantity.
Generally the following two base values are chosen:
The base power = nominal power of the equipment
The base voltage = nominal voltage of the equipment
[3 marks]
2. Explain the advantages of using per unit in power system. (CLO1:C2)
When values are expressed in p.u, the comparison of electrical quantities with their
"normal" values is straightforward
The values of impedances expressed in p.u stay fairly constant whatever the power
and voltage ratings.
The calculations using the per unit system are simplified.
[3 marks]
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3. Calculate the Z p.u if S base = 15 kVA, I base = 1200 A and Z actual = 10 (CLO1:C3)
5. Four sets of 12 kV generator were connected in parallel to a bus-bar having a rating of
25MVA, 0.07 p.u, 65MVA, 0.13 p.u, 48MVA, 0.32 p.u and 27MVA, 0.15 p.u
respectively. If fault occur at the bus bar, and by using 55MVA as a base value,
calculate:
i. The short circuit apparent power, Ssc
G1 G2 G3 G4
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ii. The short circuit current, Isc
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