Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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Number 9

2.
to
The only drawback of PM motors is the rela-
uvely high cost of the magnets and the inability to
obtain higher speeds by field weakening.
b. The m
A separat
1200 r/m
12
to a 115
voltage r
1500 r/m
Questions and Problems
Practical Level
The follo
13
Name three types of dc motors and make a
250 hp, 2
sketch of the connections.
nominal
Explain what is meant by the generator ef-
insulatio
fect in a motor.
weight: 3
What determines the magnitude and polarity
cdocu
Couzed
3.
of the counter-emf in a dc motor?
external
4.
The counter-emf of a motor is always ed
slightly less than the applied armature volt-
length of
a. Calcu
at full
b. Calcu
age. Explain.
5.
Name two methods that are used to vary the
speed of a dc motor.
exciti
9.
Explain why the armature current of a shunt
motor decreases as the motor accelerates.
20 pe
c. Calcu
resist
7 Why is a starting resistor needed to bring a
motor up to speed?
know
at ful
d. If we
8 Show one way to reverse the direction of ro-
tation of a compound motor.
what
A 230 V shunt motor has a nominal arma-
curre:
6.
ture current of 60 A. If the armature resist-
14
We wish
ance is 0.15 N, calculate the following:
a. The counter-emf [V]
b. The power supplied to the armature [W]
c. The mechanical power developed by the
motor, [kW] and [hp]
10 a. In Problem 9 calculate the initial starting
current if the motor is directly connected
across the 230 V line.
b. Calculate the value of the starting resistor
needed to limit the initial current to 115 A.
motor b"
shown in
current i
a. The v
want
curre
b. The b
O r/m
Intermediate level
15
a. The r
11 The compound motor of Fig. 12 has 1200
by us
turns on the shunt winding and 0
Transcribed Image Text:2. to The only drawback of PM motors is the rela- uvely high cost of the magnets and the inability to obtain higher speeds by field weakening. b. The m A separat 1200 r/m 12 to a 115 voltage r 1500 r/m Questions and Problems Practical Level The follo 13 Name three types of dc motors and make a 250 hp, 2 sketch of the connections. nominal Explain what is meant by the generator ef- insulatio fect in a motor. weight: 3 What determines the magnitude and polarity cdocu Couzed 3. of the counter-emf in a dc motor? external 4. The counter-emf of a motor is always ed slightly less than the applied armature volt- length of a. Calcu at full b. Calcu age. Explain. 5. Name two methods that are used to vary the speed of a dc motor. exciti 9. Explain why the armature current of a shunt motor decreases as the motor accelerates. 20 pe c. Calcu resist 7 Why is a starting resistor needed to bring a motor up to speed? know at ful d. If we 8 Show one way to reverse the direction of ro- tation of a compound motor. what A 230 V shunt motor has a nominal arma- curre: 6. ture current of 60 A. If the armature resist- 14 We wish ance is 0.15 N, calculate the following: a. The counter-emf [V] b. The power supplied to the armature [W] c. The mechanical power developed by the motor, [kW] and [hp] 10 a. In Problem 9 calculate the initial starting current if the motor is directly connected across the 230 V line. b. Calculate the value of the starting resistor needed to limit the initial current to 115 A. motor b" shown in current i a. The v want curre b. The b O r/m Intermediate level 15 a. The r 11 The compound motor of Fig. 12 has 1200 by us turns on the shunt winding and 0
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