Delmar's Standard Textbook Of Electricity
7th Edition
ISBN: 9781337900348
Author: Stephen L. Herman
Publisher: Cengage Learning
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You are working as a plant electrician. You are told that a large DC motor was returned from the rewind shop and was installed on the previous shift. The motor seemed to operate properly until load was added. The motor then stopped, reversed direction, and began to run at high speed. What is the probable cause of the trouble, and what would you do to correct the problem? Explain your answer.
23. When the circuit breaker is always tripping, most likely
There is an overloading
c. The supply line are open
a.
b.
There is an over current
d. The load is removed
24. The synchronous motor is not inherently self- starting because
the rotating magnetic field does not have enough poles
b. the rotating magnetic field is produced by only 50 HZ frequency currents
the force required to accelerate the rotor is to the synchronous speed in an instant is
d. the starting devices to accelerate the rotor to near synchronous speed is absent
25. Synchronous motor has speed
a. slight drop in speed on full load
b.high speed at low torque
а.
с.
c. constant speed
d. low speed at high -
L1. It common practice to provide access to the interpole windings on machines designed to be used as motors or generators. a) is b) is not c) neither "a" nor "b" L2. The direction of rotation of a DC motor is referenced from the commutator end of the motor. a) true b) false L3. How may the direction of rotation of a DC motor be reversed? a) by reversing the direction of current flow in the armature conductors b) by reversing the polarity of the magnetic field poles c) either "a" or "b" d) neither "a" nor "b"
Chapter 30 Solutions
Delmar's Standard Textbook Of Electricity
Ch. 30 - Prob. 1RQCh. 30 - Prob. 2RQCh. 30 - Prob. 3RQCh. 30 - Prob. 4RQCh. 30 - What type of motor is known as a constant-speed...Ch. 30 - What is CEMF?Ch. 30 - Prob. 7RQCh. 30 - Prob. 8RQCh. 30 - Prob. 9RQCh. 30 - What type of motor should never be operated at no...
Ch. 30 - Prob. 11RQCh. 30 - What is the most common way of changing the...Ch. 30 - Prob. 13RQCh. 30 - Prob. 14RQCh. 30 - What device is used to disconnect power to the...Ch. 30 - Prob. 16RQCh. 30 - Who was the first person to establish a...Ch. 30 - One horsepower is equal to how many W?Ch. 30 - A motor is operating a load that requires a torque...Ch. 30 - The motor in Question 19 is connected to a 250-VDC...Ch. 30 - Prob. 1PA
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- What is the name of the voltage when the field current is zero of the open circuit of the DC generator? a. rated voltage b. Generated EMF c. Back emf d. Residual voltage Clear my choicearrow_forwardAppliances in home that use DC motor and briefly explain why it works as reverse DC generatorarrow_forwardQ2: b- Explain how does the three- phase induction motor work? *arrow_forward
- Q choose the correct answer: 1-Brushless excitation system consisting of.... a- Stator field winding and power diodes b-stator and rotor field winding and capacitor c- stator and rotor field winding and capacitor d- Everything mentioned in the options 2- Voltage generated per phase in an alternator is proportional to a- Flux per pole b- Number of turns in armature c-Winding factors d- Everything mentioned in the options e- Frequency of waveform 3- If input mech. Power of SG constant, the functionality of AVR is a- Control flux of rotor b-Control terminal voltage c- Control flux and terminal voltage d-Control Load anglearrow_forwardQ3/ Chose the correct answer for the following 1. Synchronous motors are generally not self-starting because (a) the direction of rotation is not fixed (b) the direction of instantaneous torque reverses after half cycle (c) startes cannot be used on these machines (d) starting winding is not provided on the machines 2. The power developed by a synchronous motor will be maximum when the load angle is (a) Zero (b) 45° (c) 90° (d) 120° 3. An over-excited synchronous motor takes (a) leading current (b) lagging current (c) both (a) and (b) (d) none of the above 4. In a synchronous motor, the magnitude of stator back e.m.f. £& depends on (a) d.c. excitation only (b) speed of the motor (c) load on the motor (d) both the speed and rotor flux 5. A pony motor is basically a (a) small induction motor (c) D.C. shunt motor (b) D.C. series motor (d) double winding A.C./D.C. motorarrow_forwardANSWER ALL THE QUESTIONS: A.) Calculate the voltage induced in the armature winding of a 4 pole, wave-wound, dc machine having 728 active conductors and running at 1800rpm. The flux per pole is 30mWb. 1310.4V 468.2 V 720.4 V 236.4 V B.) The direction of rotation of a DC motor is reversed by reversing armature connections adding resistance to the field circuit interchanging the armature and field connection reversing supply connectionarrow_forward
- Two DC generators are running in parallel. One of the generators may run as a motor, what is the main reason such conditions occur? Explain your answer with the use of a calculation.arrow_forwardA. The DC motor in Figure 3 on Worksheet 8 is aa) cumulatively connected short-shunt compound DC motor b) cumulatively connected long-shunt compound DC motor c) differentially connected short-shunt compound DC motor d) shunt DC motorB. Is the DC motor in Figure 1 on Worksheet 8 turning in the same direction as that in Figure 3?a) yes b) noarrow_forwardThe factors effecting the speed of dc motor are The flux p and the voltage across the armature the voltage across the armature and the applied voltage V The applied voltage V, flux p and the voltage across the armature none of the aboye Indicate whether the following statement are true or false * True False The distance between the beginnings of each cascaded two coils is called commutator Pitcharrow_forward
- (B)-ndicate whether the following statements are true or false and correct the faise statements. -When a series d.c. motor is operate without load, the armature will not run. The strength of magnetic field in d.c. shunt generator can be varied by varying the polarity of the field poles The main disadvantage of series generators is Output voltage varies as the Toad varies There is no output from the transformer under short-circuit conditionsarrow_forwardDEGREE: ELECTRICAL ENGINEERING SUBJECT/COURSE: AC MACHINES Answer the following questions (A, B and C) depending on the topic. 1. SYNCHRONOUS MOTORS A. What is necessary to start a synchronous motor to rotate from standstill? Describe the process. B. What is meant by synchronous condenser? C. Why is it possible for synchronous motors be used as a power factor correction device and what applications do synchronous motors commonly used? Describe the operation.arrow_forwardWhich is the device in DC generators that converts AC into DC? stator brushes commutator armature This type of armature winding delivers high e.m.f. and low current. dummy or idle coils lap winding O frog-leg winding wave windingarrow_forward
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