Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Textbook Question
Chapter 31, Problem 6SQ
When the high button is depressed in Figure 31–4, what prevents the high-speed starter from closing immediately?
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The current coil of a wattmeter is connected in the red
line of a three-phase system. The voltage circuit can be
connected between the red line and either the yellow
line or the blue line by means of a two-way switch.
Assuming the load to be balanced, show with the aid
of a phasor diagram that the sum of the wattmeter
indications obtained with the voltage circuit connected
to the yellow and the blue lines respectively gives the
total active power.
A wattmeter has its current coil connected in the yellow
line, and its voltage circuit is connected between the
red and blue lines. The line voltage is 400 V and the
balanced load takes a line current of 30 A at a power
factor of 0.7 lagging. Draw circuit and phasor diagrams
and derive an expression for the reading on the wattmeter
in terms of the line voltage and current and of the phase
difference between the phase voltage and current.
Calculate the value of the wattmeter indication.
ANS:
. Line amperes × line volts × sin φ = 8750 var
4. The circuit shown below shows an infinite impedance (open circuit) in phase B
of the Y-connected load. Find the phasor voltage VOB if the system is 208 V,
sequence ABC.
-j100 Q
100 Ω
B
5. Three identical impedances of Z = 15260°2 are connected in Y to a three-phase,
three-wire, 240 V, ABC system. The lines between the supply and the load have
impedances of 2 +j 1 Q2. Find the line voltage magnitudes at the load. Find the
new values when a set of capacitors with reactance of -j10 Q (Y-connection) is
connected in parallel with the load. Draw the vector diagram for the load current,
the capacitor current and the system line current.
Chapter 31 Solutions
Electric Motor Control
Ch. 31 - Excluding slip, at what speed (r/min) will an...Ch. 31 - What is meant by the description separate winding...Ch. 31 - Prob. 3SQCh. 31 - Prob. 4SQCh. 31 - In Figure 314, what does the broken line between...Ch. 31 - When the high button is depressed in Figure 314,...Ch. 31 - Which coils are energized immediately when the...Ch. 31 - At what speed can a four-pole, 240-volt, 5-hp,...Ch. 31 - What is meant by the compelling action produced by...Ch. 31 - Prob. 10SQ
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, electrical-engineering and related others by exploring similar questions and additional content below.Similar questions
- 1. A three-phase, three-wire, 240 V, ABC system supplies a delta-connected load in which ZAB = 25/90°, ZBC = 15230° and ZCA = 200°. a) Find the line currents and the total real and reactive powers supplied by the source. Draw the phasor diagram for the line voltages and phase and line currents. Vc VA AT VB ICT 1 CA ZAB | BT ZBC b) A 240 V, 2 HP, 0.95 efficiency, single-phase motor is connected as shown below. The motor is operating at 0.85 p.f. lagging. Repeat (a). Include the motor current in the phasor diagram VA AT ZAB Ꮓ ΑΒ V B CT 1BT M ZBC ZCAarrow_forward2. A three-phase, four-wire, 208 V, ABC system supplies a Y-connected load in which Zд = 100°N, Z = 15/30° and Zc = 104-30°. Find the line currents, the neutral current and total real and reactive powers. Draw the phasor diagram of the phase voltages and currents. ZA = 3. A three-phase, three-wire, 208 V, ABC system supplies a Y-connected load in which ZA 100°, ZB = 15230° and Zc = 10-30°. Find the line currents, the phase voltages across the load impedances, the total real and reactive powers and the voltage Von VA ZAarrow_forwardDon't use ai to answer I will report you answerarrow_forward
- Discuss the importance of power-factor correction in a.c. systems. A 400 V, 50 Hz, three-phase distribution system supplies a 20 kVA, three-phase induction motor load at a power factor of 0.8 lagging, and a star-connected set of impedances, each having a resistance of 10 Ω and an inductive reactance of 8 Ω. Calculate the capacitance of delta-connected capacitors required to improve the overall power factor to 0.95 lagging. ANS: 75 µF/pharrow_forwardA 3-phase, wye-connected generator induces 2400 V in each of its windings. Calculate the line voltage.arrow_forwardwhy Low Pass filter (LPF) R₁C=S V₁ R т Tc Voarrow_forward
- Don't use ai to answer I will report you answerarrow_forwardA 60hp,3-phase motor absorbs 50 kW from a 600 V,3-phase line. If the line current is 60 A, calculate the following: a. The efficiency of the motor b. The apparent power absorbed by the motor c. The reactive power absorbed by the motor and the power factor of the motorarrow_forwardThree 15Ω resistors and three 8Ω reactors are connected as shown in Fig. 18. If the line voltage is 530 V, calculate the following: a. The active, reactive, and apparent power supplied to the 3 -phase load b. The voltage across each resistorarrow_forward
- Three resistors are connected in delta. If the line voltage is 13.2kV and the line current is 1202 A, calculate the following: A) the current in and the voltage acroos each resistor B) The power supplied to each resistor and the 3 phase load C) The ohmic value of each resistorarrow_forwardWith the aid of a phasor diagram show that the active power and power factor of a balanced three-phase load can be measured by two wattmeters. For a certain load, one wattmeter indicated 20 kW and the other 5 kW after the voltage circuit of this wattmeter had been reversed. Calculate the active power and the power factor of the load. ANS: 15 kW, 0.327arrow_forwardState the advantages to be gained by raising the power factor of industrial loads. A 400 V, 50 Hz, three-phase motor takes a line current of 15.0 A when operating at a lagging power factor of 0.65. When a capacitor bank is connected across the motor terminals, the line current is reduced to 11.5 A. Calculate the rating (in kVA) and the capa citance per phase of the capacitor bank for: (a) star connection; (b) delta connection. Find also the new overall power factor. ANS: 3.81 kvar, 70.5 µF, 23.5 µF, 0.848 laggingarrow_forward
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