SECTION B-Choose any TWO (2) Questions from this Section Question 1 [25 Marks] (a) A commercial building has a power demand of 50 kW at a power factor of 85%. Determine (i) (ii) The annual penalty if the utility's minimum power factor is 95% and the cost of power is P10/kW/month (9) P The cost of capacitor, which when connected in parallel to the load will improve the power factor to 100%. (Assume the purchasing cost of capacitor is P30/kVAR) (10) (b) A 3-phase, 10 kVA load has a power factor of 0.342. The power is measured by two wattmeter method. Find the reading of each wattmeter. Q w Var Va = 10€ Va >= 10kVA pl: 0.36 2 (= Isine 5 3149 Question 2 [25 Marks] (a) A single-phase motor takes apparent power of 1909 VA at a power factor of 0.866 lagging when con- nected to a 230 V, 50 Hz supply. (i) Calculate current drawn from the supply (ii) (b) Draw a fully labelled equivalent circuit of a transformer Two similar capacitors are then connected in parallel with each other to form a capacitance bank. The capacitor bank is now connected in parallel with the motor to raise the power factor to 0.95. Calculate the capacitance of each capacitor.. (2) Cif (tune (14) (8) Question 3 [25 Marks] Quy (a) A cable is required to supply current from a 110 V a.c. source to a welding set. The welding set has a power factor of 0.6 lagging and taking a current of 200 A from the source. The only avail- able cable has a rating of 150 A, and it is decided to use this cable by installing a capacitor across the terminals of the welding set. (i) Calculate the capacitive current required to limit the cable current to 150 A. (i) Draw a fully labelled vector diagram showing all currents (8) (6) (b) A 3-phase, 400 V source is supplying power to a balanced 3-phase delta connected 12 kW load and the line current is 30 A. If the same load is connected in star find (i) Line current IL (ii) Power factor pl V (iii) Power consumed (4) (3) (4) Io I a lave = tan" Pelts (13 (PLA)) p=0.6 I 200 12kW I₁ = 30A Zp ACI 130L Star Page 3 of 3 Ic Si, Tou

SECTION B-Choose any TWO (2) Questions from this Section Question 1 [25 Marks] (a) A commercial building has a power demand of 50 kW at a power factor of 85%. Determine (i) (ii) The annual penalty if the utility's minimum power factor is 95% and the cost of power is P10/kW/month (9) P The cost of capacitor, which when connected in parallel to the load will improve the power factor to 100%. (Assume the purchasing cost of capacitor is P30/kVAR) (10) (b) A 3-phase, 10 kVA load has a power factor of 0.342. The power is measured by two wattmeter method. Find the reading of each wattmeter. Q w Var Va = 10€ Va >= 10kVA pl: 0.36 2 (= Isine 5 3149 Question 2 [25 Marks] (a) A single-phase motor takes apparent power of 1909 VA at a power factor of 0.866 lagging when con- nected to a 230 V, 50 Hz supply. (i) Calculate current drawn from the supply (ii) (b) Draw a fully labelled equivalent circuit of a transformer Two similar capacitors are then connected in parallel with each other to form a capacitance bank. The capacitor bank is now connected in parallel with the motor to raise the power factor to 0.95. Calculate the capacitance of each capacitor.. (2) Cif (tune (14) (8) Question 3 [25 Marks] Quy (a) A cable is required to supply current from a 110 V a.c. source to a welding set. The welding set has a power factor of 0.6 lagging and taking a current of 200 A from the source. The only avail- able cable has a rating of 150 A, and it is decided to use this cable by installing a capacitor across the terminals of the welding set. (i) Calculate the capacitive current required to limit the cable current to 150 A. (i) Draw a fully labelled vector diagram showing all currents (8) (6) (b) A 3-phase, 400 V source is supplying power to a balanced 3-phase delta connected 12 kW load and the line current is 30 A. If the same load is connected in star find (i) Line current IL (ii) Power factor pl V (iii) Power consumed (4) (3) (4) Io I a lave = tan" Pelts (13 (PLA)) p=0.6 I 200 12kW I₁ = 30A Zp ACI 130L Star Page 3 of 3 Ic Si, Tou

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.7MCQ: Consider Figure 3.5. Match the following, those on the left to those on the right. (i) Im (a)...

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