ELECTRICITY FOR THE TRADES W/ACCESS
3rd Edition
ISBN: 9781264605309
Author: Petruzella
Publisher: MCG
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Chapter 7.2, Problem 14RQ
Calculate the unknown value for each circuit (a) through (c) listed in the following table.
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A dc compound motor having a rating of 10 kW,
1150 r/min, 230 V, 50 A, has the following losses at
full-load:
bearing friction loss
40 W
brush friction loss
==
50 W
windage loss
=
200 W
(1)
total mechanical losses
=
290 W
(2)
iron losses
=
420 W
(3)
copper loss in the shunt field
=
120 W
copper losses at full-load:
(4)
a. in the armature
b. in the series field
c. in the commutating winding
total copper loss in the
500 W
25 W
70 W
armature circuit at full-load
=
595 W
4 What determines the power rating of a ma-
chine?
-5 If we cover up the vents in a motor, its out-
put power must be reduced. Explain.
-6 If a motor operates in a cold environment,
may we load it above its rated power? Why?
An electric motor driving a skip hoist with-
draws 1.5 metric tons of minerals from a
trench 20 m deep every 30 seconds. If the
hoist has an overall efficiency of 94 percent,
calculate the power output of the motor in
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Chapter 7 Solutions
ELECTRICITY FOR THE TRADES W/ACCESS
Ch. 7.1 - What is the base unit and symbol used for...Ch. 7.1 - Write the metric prefix and symbol used to...Ch. 7.1 - Convert each of the following: a. 2,500 to...Ch. 7.2 - State Ohms law.Ch. 7.2 - List the three formulas associated with Ohms law.Ch. 7.2 - Calculate the unknown value for each circuit (a)...Ch. 7.2 - A pilot lamp with 12 volts applied to it draws a...Ch. 7.2 - A resistor has a resistance of 220 . The current...Ch. 7.2 - An electric soldering iron with a 40- heating...Ch. 7.2 - A baseboard heater draws a current of 8 A when...
Ch. 7.2 - A sensor module has an internal resistance of...Ch. 7.2 - The current through and the voltage drop across a...Ch. 7.2 - The heating element for an electric floor heating...Ch. 7.2 - How much power is lost in the form of heat when 25...Ch. 7.2 - The voltage drop across a 330- resistor is...Ch. 7.2 - A digital multimeter display indicates a reading...Ch. 7.2 - Calculate the unknown value for each circuit (a)...Ch. 7.2 - Assume that applying 120 volts to a resistive load...Ch. 7.2 - The voltage drop across a 10-W, 330- resistor is...Ch. 7.2 - The cold resistance of a tungsten lamp filament is...Ch. 7.2 - An electric baseboard heater is rated for 1200 W...Ch. 7.2 - A lamp dimmer switch is rated for 5 A at 120 V....Ch. 7.2 - A 400-W 4- public address speaker is to be fused...
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