Delmar's Standard Textbook of Electricity (MindTap Course List)
6th Edition
ISBN: 9781285852706
Author: Stephen L. Herman
Publisher: Cengage Learning
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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
horsepower and in kilowatts.
Chapter 31 Solutions
Delmar's Standard Textbook of Electricity (MindTap Course List)
Ch. 31 - Prob. 1RQCh. 31 - Prob. 2RQCh. 31 - Prob. 3RQCh. 31 - Prob. 4RQCh. 31 - What type of motor is known as a constant-speed...Ch. 31 - What is CEMF?Ch. 31 - Prob. 7RQCh. 31 - Prob. 8RQCh. 31 - Prob. 9RQCh. 31 - What type of motor should never be operated at no...
Ch. 31 - Prob. 11RQCh. 31 - What is the most common way of changing the...Ch. 31 - Prob. 13RQCh. 31 - Prob. 14RQCh. 31 - What device is used to disconnect power to the...Ch. 31 - Prob. 16RQCh. 31 - Who was the first person to establish a...Ch. 31 - One horsepower is equal to how many W?Ch. 31 - A motor is operating a load that requires a torque...Ch. 31 - The motor in Question 19 is connected to a 250-VDC...Ch. 31 - Prob. 1PA
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- The efficiency of a motor is always low when it operates at 10 percent of its nominal power rating. Explain.arrow_forwardA dc motor connected to a 240 V line pro- duces a mechanical output of 160 hp. Knowing that the losses are 12 kW, calculate the input power and the line current.arrow_forwardA 115 V dc generator delivers 120 A to a load. If the generator has an efficiency of 81 percent, calculate the mechanical power needed to drive it [hp].arrow_forward
- A machine having class B insulation attains a temperature of 208°C (by resistance) in a torrid ambient temperature of 180°C. a. What is the temperature rise? b. Is the machine running too hot and, if so, by how much?arrow_forward1 Name the losses in a dc motor. 2 What causes iron losses and how can they be reduced? -3 Explain why the temperature of a machine increases as the load increases.arrow_forward20. A tractor weighing 14 kN with a wheel base of 3m carries an 8 kN load on its rear wheel. Compute the maximum bending moment and shear when crossing a 4.5 span. Consider the load only at the wheels.arrow_forward
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- Assignment #2 A 110-V, three-phase, Y-connected, 8 pole, 48-slot, 6000-rpm, double-layer wound, synchronous generator has 12 turns per coil. If one side of the coil is in slot 1, the other side is in slot 6. There are 4 parallel paths. When the generator delivers the rated load at a line voltage of 110 V, the voltage regulation is 5%. What is the flux per pole? Draw two consecutive phasegroups of one of the phase windings and connect them (a) in series and (b) in parallel showing the Start (S) and Finish (F) of both connections. (A separate drawing for each connection)arrow_forward3-4 Transmissiva Live of 120km has R= 0.2 ~2/15 X= 0.8 -2/km Y = 15H/6 5/km The line is supplies a load of 45 kV, SOMW, 0.8 lead p.f find sending voltage, Sending Current p.f. Sanding Voltage Regulation ⑨Voltage 5 Ⓒ charching coming! изу usy π cct लेarrow_forwardA (medium) single phase transmission line 100 km long has the following constants : Resistance/km = 0.25 Q; Susceptance/km = 14 × 10° siemen ; Reactance/km = 0.8 Receiving end line voltage = 66,000 V Assuming that the total capacitance of the line is localised at the receiving end alone, determine (i) the sending end current (ii) the sending end voltage (iii) regulation and (iv) supply power factor. The line is delivering 15,000 kW at 0.8 power factor Lead Draw the phasor diagram to illustrate your calculations.arrow_forward
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