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4. The power taken by a 3-phase, 400-V motor is measured by the two wattmeter method and the readings of the two wattmeters are 460 and 780 watts respectively. Estimate the power factor of the motor and the line current. [0.913, 1.96 A] (City & Guilds, London)

4. The power taken by a 3-phase, 400-V motor is measured by the two wattmeter method and the readings of the two wattmeters are 460 and 780 watts respectively. Estimate the power factor of the motor and the line current. [0.913, 1.96 A] (City & Guilds, London)

Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
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1. Two wattmeters connected to measure the input to a balanced three-phase circuit indicate 2500 W and 500 W respectively. Find the power factor of the circuit (a) when both readings are positive and (b) when the latter reading is obtained after reversing the connections to the current coil of one instrument. |(a) 0.655 (b) 0.3591] (City & Guilds, London) 2. A 400-V, 3-phase induction motor load takes 900 kVA at a power factor of 0.707. Calculate the kVA rating of the capacitor bank to raise the resultant power factor of the installation of 0.866 lagging. Find also the resultant power factor when the capacitors are in circuit and the motor load has fallen to 300 kVA at 0.5 power factor. 3. Two wattmeters measure the total power in three-phase circuits and are correctly connected. One reads 4,800 W while other reads backwards. On reversing the latter, it reads 400 W. What is the total power absorbed by the circuit and the power factor? 4. The power taken by a 3-phase, 400-V motor is measured by the two wattmeter method and the readings of the two wattmeters are 460 and 780 watts respectively. Estimate the power factor of the motor and the line current. |296 kVA, 0.998 leading] (City & Guilds, London) [4400 W; 0.49| (Sheffield Univ. U.K.) [0.913, 1.96 AJ (City & Guilds, London) 5. Two wattmeters, W, and W, connected to read the input to a three-phase induction motor running unloaded, indicate 3 kW and 1 kW respectively. On increasing the load, the reading on W, increases while that on W, decreases and eventually reverses. Explain the above phenomenon and find the unloaded power and power factor of the motor. 12 kW, 0.287 lag] (London Univ.) 6. The power flowing in a 3-0, 3-wire, balanced-load system is measured by the two wattmeter method. The reading on wattmeter A is 5,000 W and on wattmeter B is – 1,000 W (a) What is the power factor of the system? (b) If the voltage of the circuit is 440, what is the value of capacitance which must be introduced into each phase to cause the whole of the power measured to appear on wattmeter A? 10.359; 5.43 (Meters and Meas. Insts. A.M.I.E.E. London) inn 1. -L-
Transcribed Image Text:1. Two wattmeters connected to measure the input to a balanced three-phase circuit indicate 2500 W and 500 W respectively. Find the power factor of the circuit (a) when both readings are positive and (b) when the latter reading is obtained after reversing the connections to the current coil of one instrument. |(a) 0.655 (b) 0.3591] (City & Guilds, London) 2. A 400-V, 3-phase induction motor load takes 900 kVA at a power factor of 0.707. Calculate the kVA rating of the capacitor bank to raise the resultant power factor of the installation of 0.866 lagging. Find also the resultant power factor when the capacitors are in circuit and the motor load has fallen to 300 kVA at 0.5 power factor. 3. Two wattmeters measure the total power in three-phase circuits and are correctly connected. One reads 4,800 W while other reads backwards. On reversing the latter, it reads 400 W. What is the total power absorbed by the circuit and the power factor? 4. The power taken by a 3-phase, 400-V motor is measured by the two wattmeter method and the readings of the two wattmeters are 460 and 780 watts respectively. Estimate the power factor of the motor and the line current. |296 kVA, 0.998 leading] (City & Guilds, London) [4400 W; 0.49| (Sheffield Univ. U.K.) [0.913, 1.96 AJ (City & Guilds, London) 5. Two wattmeters, W, and W, connected to read the input to a three-phase induction motor running unloaded, indicate 3 kW and 1 kW respectively. On increasing the load, the reading on W, increases while that on W, decreases and eventually reverses. Explain the above phenomenon and find the unloaded power and power factor of the motor. 12 kW, 0.287 lag] (London Univ.) 6. The power flowing in a 3-0, 3-wire, balanced-load system is measured by the two wattmeter method. The reading on wattmeter A is 5,000 W and on wattmeter B is – 1,000 W (a) What is the power factor of the system? (b) If the voltage of the circuit is 440, what is the value of capacitance which must be introduced into each phase to cause the whole of the power measured to appear on wattmeter A? 10.359; 5.43 (Meters and Meas. Insts. A.M.I.E.E. London) inn 1. -L-
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