POWER FACTOR CORRECTIONS Problem 827:EE Board October

A 132kV line three-phase system delivers 70.7 MVA of a balanced delta load of power factor 70.7% lagging. Determine the reactance necessary to attain unity power factor.

A. Xc = 1,092  B. Xc = 965  C. Xc = 1,142  D. Xc = 1,045 

Problem 828:EE Board October 1990

A single-phase inductive load takes 50 kVA at 0.60 power factor lagging. Solve for the kVAR of a capacitor required to improve the power factor to 1.0.

A. 30 kVAR B. 20 kVAR C. 22.5 kVAR D. 40 kVAR

Problem 829:

A single-phase load on 220 V takes 5 kW at 0.6 lagging power factor. Find the kVAR size of capacitor, which maybe connected in parallel with this motor to bring the resultant power factor to 1.0.

A. 6.67 B. 7.32 C. 8.66 D. 6.26

Problem 830:

A 5 hp, 220 V, 60 Hz, single-phase induction motor operates at an efficiency and power factor of 0.88 and 0.8 respectively. What capacitance should be connected across the motor in order for the feeder supplying this motor to operate at unity power factor?

A. 201.55 F B. 183.52 F C. 174.22 F D. 212.56 F Problem 831:EE Board October 1987

Installed in one of the customer of CEPALCO are two single phase transformers each rated 75 kVA are connected V or open delta to serve a 3-phase load of 120 kW at 0.8 pf lagging. To prevent the overloading of the transformers, determine the size of the capacitor in kVAR.

A. 40 B. 41 C. 39 D. 42

Problem 832:

Three transformers each rated 100 kVA are connected delta supplying a load of 160 kW at 0.8 pf lagging. One of the transformers is taken for repair and the rest are connected open delta. What kVAR (minimum) of capacitor must be connected with the load so that the load of the remaining transformers will be 95% of their combined rated capacities.

A. 85.32 B. 81.62 C. 87.58 D. 80.92

Problem 833:EE Board October 1993

Three single- phase transformers each rated 75 kVA are banked in delta and supplying a 3- phase load drawing 160 kVA at 0.8 lagging power factor. If one transformer is removed for repairs, solve for the minimum amount in kVAR of capacitor needed to prevent overloading of the remaining units.

A. 70.32 B. 73.64 C. 72.46 D. 73.28

Problem 834

Two single- phase transformer each rated 150 kVA are connected open delta supplying a three- phase induction motor rated 250 hp, 0.7 pf and 80% efficiency. Determine the minimum size in kVAR of a capacitor needed to prevent overloading the transformers.

A. 135 B. 126 C. 120 D. 123

Problem 835: EE Board October 1982

Two single- phase transformers are each rated 75 kVA are connected in V or open delta to serve a 3- phase load of 120 kW at 0.80 power factor lagging. Determine the size in kVAR of the capacitor needed to prevent overloading of the transformers.

A. 40.25 B. 41.28 C. 45.24 D. 43.50

Problem 836: EE Board April 1984

A plant has a load of 290 kilowatt with an average power factor of 70%. The owner requests you to correct the power factor to reduce its power consumption. How much capacitor kVAR is required to increase the power factor to 90%?

A. 152.46 B. 155.39 C. 150.34 D. 154.58

Problem 837: EE Board October 1982

A 150-kVA-transformer bank will serve a load expected to draw 135 kW at 0.80 lagging power factor. Solve for the size of the capacitor bank needed to be added in order to prevent overloading of the transformer bank.

A. 32.506 kVAR B. 35.866 kVAR C. 40.391 kVAR D. 28.266 kVAR Problem 838: EE Board October 1981

A 3- phase generator has the following 3- phase loads: an inductive load drawing 400 kVA at 0.60 power factor and a resistive load drawing 80 kVA at 1.00 power factor. Solve for the size in kVAR of the capacitor bank needed to improve the power factor of the combined loads to 0.85 lagging.

A. 120.58 kVAR B. 121.68 kVAR C. 124.54 kVAR D. 122.82 kVAR Problem 839: EE Board April 1997

A load of 10,000 kVA, 80% pf lagging is connected to a 13,200 volts line. How much capacitive reactive power is needed to correct the power factor to 0.97 lagging?

A. 5,156 kVAR B. 3,138 kVAR C. 2,547 kVAR D. 4,395 kVAR Problem 840: EE Board April 1986

A short, 3- phase, 3- wire transmission line has a receiving end voltage of 4160 V phase to neutral an serving a balanced 3- phase load of 998,400 volt amperes at 0.82 pf lagging. At the receiving end the voltage is 4600 V phase to neutral and the pf is 0.77 lagging. Solve for the size in kVAR of the capacitor needed to improve the receiving end pf to 0.9 lagging maintaining 4160 V.

A. 181 B. 175 C. 172 D. 178

Problem 841:

A short, 3- phase, 3- wire transmission line has an impedance per wire of 3 + j7 ohms, the receiving end load is 1950 kW, 0.65 pf lagging with the line voltage of 13,200 V. determine the kVAR of the capacitor to be connected at the receiving end to make the pf at that end to 0.8 lagging.

A. 824.56 B. 871.45C. 803.88 D. 817.32

Problem 842: EE Board October 1980

A balanced, 500 kVA, 3- phase, 440 volt, 60 Hz inductive load operates at a pf of 75%. Determine the total capacitor kVAR required improving the pf to 95%.

A. 207.46 B. 176.42 C. 210.75 D. 192.21

Problem 843: EE Board March 1998

A single- phase induction motor is rated 5 hp, 75% power factor and 220 volts. What approximate size of the capacitor size is necessary to raise the power factor to about 95%?

A. 3 kVARB. 2 kVARC. 2.5 kVAR D. 3.5 kVAR

Problem 844: EE Board October 1984

A balanced 3-phase load draws 150 A phase current at 7.5 kV phase to neutral, 0.891 power factor lagging. It is desired to raise the power factor to 0.96 leading. Solve for the amount of capacitor kVAR needed to achieve such pf.

A. 2273 kVAR B. 2409 kVAR C. 2509 kVAR D. 2365 kAVR Problem 845:EE Board April 1981

A 3-phase, 3-wire, short transmission line has a resistance of 3 ohms and a reactance of 8 ohms per wire. At the receiving end, a balanced 3-phase load draws a line current of 60 A, at 13,500 V, solve the size in kVAR of capacitors needed to raise the power factor at the receiving end to 0.95 leading.

A. 1043.5 B. 1154.2 C. 1026.5 D. 1232.2

Problem 846:

The input to an induction motor from a 13 kV, 60 Hz line is 1000 kVA, at 0.8 pf lagging. A capacitor is placed in parallel with the motor to improve the pf. Calculate the capacitance required raising the power factor to 0.9 leading.

A. 62 F B. 50 F C. 43 F D. 56 F

Problem 847:EE Board April 1981

A three-phase balanced load draws a line current of 80 A at 0.90 lagging power factor. Solve the minimum size in kVAR of the capacitor bank needed to raise the power factor to 0.95 leading, if the line to line voltage is 13,200 volts.

A. 1310.15 B. 1338.25 C. 1247.54 D. 1430.12

Problem 848:EE Board October 1990

Two Y-connected, 50 rise induction motors are fed by a 4160 V, line to line, 3-phase 60 Hz motor-control center 20 feet away. Motor #1 drives a 600-hp compressor. The efficiency of this motor is 90% and its power factor is 0.5. Instruments of motor #2 indicate 1730 kW, 277 amperes. Determine the capacity in microfarads per phase of a wye-connected bank that is required to correct the power factor of the total load to 0.966 lagging.

A. 172.4 F B. 193.8 F C. 167.2 F D. 182.1 F Problem 849:

A 2.3 kV three-phase system supplies a 120-kW, 0.6 pf lagging balanced load. Determine the capacitance in each phase of a wye-connected capacitor bank to adjust the power to 0.90 lagging.

A. 51.1 F B. 52.2 F C. 62.5 F D. 78.2 F Problem 850:EE Board October 1996

A single-phase, 60 Hz, 5 hp squirrel cage induction motor draws a current of 53 A at 117 V. If it has a 78.5% electrical to mechanical conversion efficiency, what capacitance should be connected at the terminals of the motor in order to increase the power factor of the load combination to 92%?

A. 480 F B. 380 F C. 320 F D. 420 F Problem 851:EE Board April 1989

A three-phase, 60 Hz, 2200 volts induction motor develops 500 HP, 0.8 lagging pf and efficiency of 94%. The power factor is raised to 0.90 lagging by connecting a bank of condensers in delta across the lines. If each of the capacitance unit is built up of four similar 550 V condensers, calculate the capacitance of each condenser.

A. 77.04 F B. 75.42 F C. 76.12 F D. 72.30 F Problem 852:EE Board April 1993

A star-connected 400 Hp (metric), 2000 V, 50 c/s motor works at a power factor of 0.7 lagging. A bank of mesh-connected condensers are used to raise the power factor to 0.93 lagging. Calculate the capacitance of each unit required if each is rated 500 V, 50 c/s. The motor efficiency is 85%.

A. 194 F B. 225 F C. 302 F D. 233 F Problem 853:

A factory draws a lagging load of 2000 kW at a power factor of 60% from a 6 kV bus line. A synchronous capacitor is installed to raise the overall power factor to unity. Assuming the synchronous capacitor losses are 275 kW, calculate the operating power factor of the synchronous capacitor.

A. 0.201 leading B. 0.103 leading C. 0.302 leading D. 0.113 leading Problem 854:

A 400-V three-phase balanced load takes 40 A at a lagging power of 0.8. An over- excited synchronous motor is connected to raise the power factor to unity. If the mechanical output of the motor is 15 hp and its efficiency is 85%, find the kVA input to the motor.

A. 24.2 kVA B. 18.7 kVA C. 20.3 kVA D. 21.2 kVA Problem 855:

A three-phase load of 100 kVA operates at 0.707-pf lagging. Solve for the operating power factor of a synchronous condenser necessary to raise the system power factor to 0.866 lagging, and so arrange that the system apparent power is the same as before the correction.

A. 0.632 leading B. 0.882 leading C. 0.705 leading D. 0.609 leading Problem 856:

An industrial plant has an electrical load of 5000 kW at 80% pf lagging. It has been decided to replace a 500-hp induction that drives a pump. This motor operates at an efficiency of 90% and a pf of 0.9 lagging. If a synchronous motor is purchased as a replacement, which is capable of operating at 0.80 pf leading. What will be the new plant pf. Assume the synchronous motor to have the same efficiency.

A. 0.863 B. 0.823 C. 0.837 D. 0.852 Problem 857:

A synchronous motor is drawing 60 kW is connected in parallel with a load drawing 250 kW at a lagging power of 0.8. If the combined load has a power factor of 0.9, at what power factor is the synchronous motor operating?

A. 0.862 leading B. 0.849 leading C. 0.868 leading D. 0.874 leading Problem 858:EE Board October 1985

An inductive load consumes 10 kW at 0.75 pf lagging. A synchronous motor with a pf of 0.9 leading is connected in parallel with the inductive load. What is the minimum required kW size of the synchronous motor so that the combined load will have a pf of 0.8 lagging.

A. 1.068 kW B. 1.203 kW C. 1.075 kW D. 1.109 kW Problem 859:EE Board April 1980, EE Board April 1992

An industrial plant draws 500 kW at 0.6 power factor from a three-phase system. In order to raise the power factor to 0.866 lagging and to supply needed additional power, a synchronous motor is added . This motor draws 300 kW, bringing the new total plant load to 800 kW. Neglecting the losses of the synchronous motor, calculate the exact required kVA rating.

A. 363.24 Kva B. 345.34 kVA C. 393.34 kVA D. 307.35 kVA Problem 860:

An induction motor load of 1500 kW consists of several units in parallel, operating at an average power factor of 0.80 lagging. In order to improve the power factor, a portion of the induction motor loads is to be replaced by a synchronous motor, operating at the same efficiency as the induction motors and at a power factor of 0.70 leading. Find the kVA rating of the synchronous motor required bringing the power factor of the total load to 0.90 lagging. Assume the induction motor load, which has to be replaced, operates at the same pf as the induction motor group.

A. 332 kVA B. 325 kVA C. 300 kVA D. 322 kVA

Problem 861:

An alternator rated 530-kVA, is operating at 0.60 pf lagging. A synchronous condenser is in parallel to improve the pf to 90% lagging. Determine the operating power factor of the synchronous condenser. Assume the alternator is not supposed to be overloaded.

A. 0.546 leading B. 0.447 leading C. 0.643 leading D. 0.593 leading Problem 862:

An over-excited synchronous motor is connected across a 150 kVA, 0.70 lagging power factor load. The motor takes 12 kW while running on no-load. Calculate the kVA rating of the motor required in order to bring the overall pf of the motor-inductive load combination to unity.

A. 106.22 B. 107.78 C. 110.20 D. 105.58

Problem 863:

An industrial load takes 250 kW at 60% pf from a 600 V, 60 Hz, 3-phase feeder. It is desired to raise the pf of the entire feeder to 90% by means of a synchronous motor, which at the same time is to drive a dc compound generator, requiring that the synchronous motor takes 70 kW from the line. Determine the required current rating of the synchronous motor.

A. 175.53 A B. 184.37 A C. 192.65 A D. 188.44 A Problem 864:EE Board April 1998

An existing industrial plant has an average load of 900 kW at 0.6 pf lagging. To raise the overall power factor to 0.92, a synchronous motor driving a DC generator is to be installed. If the input of the synchronous motor will be 250 kW, calculate its kVA input rating.

A. 753 kVA B. 788 kVA C. 723 kVA D. 715 kVA

TEST 24 – FAULTS ON ELECTRICAL SYSTEM