Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Textbook Question
Chapter 20, Problem 1SQ
Using the schematic diagram in Figure 20–23, determine the number of control wires needed to control the three-phase motor. Use the terminal and wire identification shown in the schematic as well as proper power circuit identification.
FIG. 20–23
Expert Solution & Answer
To determine
Calculate the number of control wires required to control the three-phase motor in Figure 20–23.
Explanation of Solution
The 3 wires are connected to the externally operated disconnect switch, and the switch is connected to pull box through 3 wires. Four wires are used to connect stations 1 and 2. Four wires and three wires are used to connect station 2 and station 3 to pull box, respectively. The pull box is connected to motor starter using 6 wires, and finally, starter is connected to a three-phase motor using 3 wires. Redraw the given figure with the representation of the required control wires as shown in Figure 1.
Conclusion:
Thus, the number of control wires required to control the three-phase motor in Figure 20-23 is calculated.
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Students have asked these similar questions
Q2. Figure Q2 shows a block diagram with an input of C(s) and an output R(s).
a)
C(s)
K₁
R(s)
K2
1 + 5s
1+2s
Figure Q2. Block diagram of control system.
Simply the block diagram to get the transfer function of the system C(s)/R(s).
b)
What is the order of the system?
c)
What is the gain of the system?
d) Determine the values of K₁ and K₂ to obtain a natural frequency w of
0.5 rad/s and damping ratio of 0.4.
e) What is the rise time and overshoot of the system with a unit step input?
Q4.
a) A purely derivative controller (i.e. with a zero at the origin only) is defined
by an improper transfer function. Considering its asymptotic behaviour,
explain why a purely derivative controller is difficult to implement in
practice. Relate your explanation to the potential limitations on system
performance.
b) Discuss the potential issues faced by a control system with a large cut-off
frequency. Relate your discussion to the implications on system
performance.
c)
The transfer function of a lag compensator is given by
2
KPID(S) = 2.2++0.2s
S
By using the asymptotic approximation technique:
(i) Obtain the standard form and corner frequency for each individual
component of KPID(S).
(ii) Clearly describe the asymptotic behaviour of each individual
component of KPID(S).
Module Code: EN2058
Q1. a) List the advantages and disadvantages of a closed loop system compared to
an open loop system.
b)
c)
What is the procedure for designing a control system for a bread toaster?
An RC circuit is given in Figure Q1. vi(t) and v(t) are the input and output
voltages.
(i) Derive the transfer function of the circuit.
(ii) With a unit step change vi(t) applied to the circuit, derive and sketch the
time response of the circuit.
R1 R2
v₁(t)
R3 C1
vo(t)
R₁ =R2 = 10 k
R3 = 100 kn C₁ = 100 μF
Figure Q1. RC circuit.
(iii) Assuming zero initial conditions, obtain the impulse and ramp responses
of the circuit from the step response derived in (ii). Sketching is not
needed.
Chapter 20 Solutions
Electric Motor Control
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