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]

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]

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

ii. The short circuit current, Isc