ELEC 212 Three-Phase Questions (1)

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San Joaquin Valley College, Temecula *

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212

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Electrical Engineering

Date

Apr 3, 2024

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docx

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San Joaquin Valley College ELEC 212 Three-Phase Questions Overview Provide answers to the questions below. Refer to this topic’s reading assignments for help with finding the answers. Questions 1. How many degrees out of phase with each other are the voltages of a three-phase system? 120 degrees 2. What are the two main types of three-phase connections? Delta and Wye 3. A wye-connected load has a voltage of 480 V applied to it. What is the voltage dropped across each phase? 1.28 277.136V 4. A wye-connected load has a phase current of 25 A. How much current is flowing through the lines supplying the load? 25A 5. A delta connection has a voltage of 560 V connected to it. How much voltage is dropped across each phase? 560V 6. List the three kinds of electrical loads that are connected to an AC circuit. Resistive, Inductive, and Capacitive 7. An electrician uses a clamp-on ammeter and a voltmeter to measure the current and voltage of a motor. If the two values are multiplied, is the product the true power or the apparent power? Then the two values are Apparent power What would you need to know to be able to calculate the other power value? Three-Phase Questions ELEC 212 Revised: 03.21 jh Academic Affairs Department

San Joaquin Valley College ELEC 212 Three-Phase Questions True power knowing the power factor of the motor 8. The ballast in some of the older florescent luminaires was said to have a low power factor. What device was added to the circuit to improve the power factor? To improve power factor, capacitor is added to the circuit. 9. What effect does the power factor of a motor have on the branch circuit supplying power to the motor Power losses go up as the square of the apparent power. A power factor of 0.7 means an apparent power of 1.4 times the true power, with nearly double the losses compared to a power factor of one. Higher capacity circuit breakers will be needed on the branch circuit where the motor is used. 10. Inductive reactance, resistance, and impedance are all measured in ohms. What is the common characteristic that makes this possible? Inductive reactance is the measure of opposition to the current flow by inductor. Resistance is the measure of opposition offered by a resistor and the impedance is the measure of opposition offered by the overall circuit. As all these quantities are used to measure the opposition offered to the flow they have same unit named as ohms Submission Submit your completed assignment to the appropriate dropbox Three-Phase Questions ELEC 212 Revised: 03.21 jh Academic Affairs Department

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