Studydroid is shutting down on January 1st, 2019



keywords:
Bookmark and Share



Front Back
A short circuit having minimum resistance
dead short
The physical motion resulting from the forces of magnetic fields
motor action
What causes counter emf in a DC motor
generator action
A continuation of current flow within an electrical cell when there is no external load
local action
What is meant by back EMF
a voltage applied in the reverse direction
What motor characteristic is affected by counter emf
speed
Speed of dc motor is
inversely proportional to flux per pole
For 20% increase in current, the motor that will give the greatest increase in torque is __ motor
series
DC shunt motor speed can be controlled electronically by using a __ in series with the armature winding
thyristor
In controlling motor speed, the SCR\'s control the
firing angle
What determines the amount of slip in an induction motor
load
What is used to counteract armature reactions
interpoles
Low speed alternators are driven by
hydraulic turbine
High speed alternators are driven by
steam turbine
Generation opf voltage in a generator can only happen when
there is a relative motion between conducting wires and magnetic lines of force
Two essential parts in rotating generators
electro/permanent magnets and armature winding
In electrical machines, what type of voltage is generated at the armature winding
AC
An elementary generator consists of a single coil rotating in a magnetic field. Why is NO voltage induced in the coil as it passes through the neutral plane
Flux lines are too dense
This machine can create a charge buildup large enough to produce a spark several centimeters long
Van de graff generator
Electrical machines that converts ac voltage to dc voltage, or vice versa
rotary converter
What converter must be used if one wished to change DC-voltage into AC-voltage
inverter
Motors are used to convert electrical energy to mechanical energy. What type of motor that is best suited for heavy-load application
polyphase motors
In a compound generator, which field winding usually has a lower resistance
series field winding
Which winding in a DC-compound generator that is relatively made of fine wires
shunt field winding
If an AC generator is to be driven from a prime mover having variable speed, such as aircraft engine, a __ must be used
constant speed drive (CSD)
In electro-mechanical conversion devices like generators and motors, the reason why a small air gap is left between the rotor and stator is to
permit mechanical clearance
What makes the drum-type armature more efficient than the gramme-ring armature
The drum-type armature coils are fully exposed to the magnetic field, while the gramme-ring armature coils are only partially exposed to the magnetic field
To minimize arcing during starting of DC motors, a resistance should be added to limit the current in the
armature winding
One causes why the shaft torque is less than the developed armature torque of a DC motor
friction loss
The running speed of a dc series motor is greatly affected by what factor
load
The main drawback of a DC shunt generator is __
Terminal voltage drop considerably with load
In alternators, what is the purpose of damper windings
it prevents hunting
The alternators driven by __ do not have a tendency to hunt
steam turbines
Description used for generators trying to self-adjust its parameters before paralleling with on line generators
jogging
The purpose of the excited in an alternator is to
provide DC field excitation
What are the two basic types of alternators
rotating field and rotating armature
The synchronous reactance of an alternator is due to
armature reaction
In alternators with low-speed prime movers, only what type of rotor may be used
salient-pole
The brush voltage drop in a dc machine is about
2 V
A 4-pole DC machine has __ magnetic circuits
4
The real working part of a DC machine is the
armature winding
In a DC motor, it can be accomplished by reversing the field connections or by reversing the armature connections
motor reversal
Intermittent sparking at the brushes of DC motors may be caused due to
an open armature coil
Why are carbon brushes preferable compared to copper brushes
they reduce sparking
A yoke of a DC machine is made of
cast steel
Series motors are also called
universal motors
Which of the following types of motors is widely used to power small appliances
universal motors
Which is the most suitable for punch presses
commutatively compounded motor
A small AC or DC generator, sometimes referred to as a rate generator, which converts its shaft speed into an electrical output. It is frequently used in servo systems to sense the velocity of a load
Tachometer
An instrument that allows viewing of rating or reciprocating objects by producing the optical effect of a slowing down or stopping motion
stroboscope
x of y cards Next > >|