Motor controls review Flashcards
(94 cards)
1
Q
Two dissimilar metals bonded together have?
A
different expansion rates
2
Q
If electrical contacts are permitted to open and close slowely
A
poor contacts are permitted to open
3
Q
A metal that remans in liquid state at room temperature.
A
Mercury
4
Q
An RTD is made out of
A
Platinum
5
Q
A bellows type thermostat works on change in
A
pressure principle
6
Q
A device that emplys the heating of two metals to produce a voltage is known as
A
thermocouple
7
Q
Two or more thermocouples connected in series
A
thermopile
8
Q
A device that works on principle of change in resistance with a change in heat is known as
A
Resistance temperature detector
9
Q
A hall generator is constructed as a
A
Integrated Circuit
10
Q
A hall sensor is used to sense the presense of a
A
Magnetic Field
11
Q
If a disk with magnetic poles around its circumferance is attatched to a rotating shaft , and a hall sensor is mounted near the disk
A
An AC voltage is produced
12
Q
Most proximity detectors will easily detect what type of metal?
A
IRON
13
Q
A proximity detector that can detect the presence of non-metallic devices usually operates on a change in
A
capacitance
14
Q
A photo conductive device changes
A
its resistance with light
15
Q
Magnetic control systerm usually operates on
A
120 volts
16
Q
A control transformer is often used to step
A
down 600v or 208v to 120v
17
Q
ANOTC contact must be connected
A
on-delay relay if its to be time delayed when closing
18
Q
Many electronic timers can be used as
A
DOE or DODE
19
Q
Pulse timers
A
continually turn off and on at regular intervals
20
Q
The most accurate way of plugging to stop a motor is with a
A
zero speed switch
21
Q
3 Main methods of braking
A
Mechanical - Dynamic - Plugging
22
Q
DOE stands for
A
delay on energization
23
Q
Typically , SCIM and their locked rotor currents cary from
A
2 1/2 to 10 times the FLA
24
Q
What kind of coupling is required for a Plugging switch
A
Direct Flexible
25
SCIM, 2 Pole @ 50 hz, ac scource will run at RPM
RPM = F x (120/ poles)
26
SCIM, 6 poles @ 60hz , ac source will run at
RPM = F x (120/ poles)
27
DOE Stands for
Delay on energization
28
the shaft of a plugging switch is most often
mechanically, connected to the shaft on the machine it controls
29
pluggin cotrol provides
rapid stop of motion
30
plugging switches are deigned to be added to control circuits
piolet device
31
Most machines in which plugging is done are driven by
SCIM
32
The rotating motion of a motor transmitted to plugging switch contacts either by a magnetic induction or by a
centrifugal mechanism
33
A plugging switch acts like a link between the motor and
reversing started
34
a starter used for a plugging switch will
interchange 2 of the 3 moter leads for a 3 phase motor
reverse direction of current through armature for a dc motor
35
when changing the direcion of motor rotation, the electrician should change connections at the scource of power or motor
scource of power or motor
36
squirrel cage induction motors are charcterized by
simplicity
reliabilty
ruggedness
37
With regard to SCM, the current
The current drops as motor speed increases
38
When a squirrel cage motor is connected directly to the plant distributionsystem at full voltage
either magnetic or manual
39
With a SCM, when voltage is reduced to start the motor the
current is also reduced and so is the machines torque
40
Which is the simplest of all starting methods
Across the line
41
Most popular motor
3 phase SCIM
42
initial inrush current is not comparable to
locked rotor current
43
With a reactr or primary resistor type starters, reactors, or resistors are
connected in series with a motor
44
It is desirable to limit the starting current of a motor if full voltage starting cause serious line disturbances on
lighting ccts
computer and electronics
fire alarm system
45
Large inrush current during starting of large motors may cause
Utility line disturbances
46
closed transition starting means the motos is
never disconnected from the line until the motor is operating at full voltage
47
Conditions where it is not acceptable to start a motor across the line due to excessive
starting current or torque
48
primary resistor starters consume
high energy and start with high power factor
49
Split phase motors will disconnect the start winding from the power line using a
centrifugal switch
50
If the motor is disconnected between the start and run stage, the starting method is refferd to as
open transition
51
Most large HP motors are started at
65%
52
some large motor circuits may use several starting because of
limitiations by the utility
torque limits of machine
length of acceleration time required
53
Autotransformers starters are considered
inductive loads
54
Some resistor and reacors starters use multiple steps of starting.
This is accomplished by tapping the resistor or reactor to provide different values of
resistanve and inductance reactance
55
autotransformers are generally employed to start what type of motor
SCIM
56
Motor started witha autotransformer reduced voltage starter
less current less torque
57
When an autotransformer is used as a voltage starter
an adjustable timer controls when the motor recieves full voltage
58
Another name for Star delta
wye-delta
59
with a star delta, if the starter used has the required number of properly wired controls the motor can be
started in wye delta
60
a star delta moto must be wound in such a manner that it iell run it
stator connected ran in delta
61
autotransformer used as a reduced vltage starter must have a minimum of
3 taps
62
with star delta motors
the full stator is used with no limiting devices
63
star delta motors are used on loads having
high inertia, short acceleration periods
64
the speed of a star delta depends on
frequency and number of poles
65
care shouldbe taken when connecting the stator windings of a star delta motor the the load, contacts will otherwisw
reverse directions when the windings are changed from wye to delta
66
the main reason to use a closed transtion starting method with a star-delta motor is to
Prevent line disturbances
67
If a set of normally closed and normally open contacts share a common terminal the contact configuration is refered to ass
single pole double throw
68
If a stator winding are connected in delta during the starting period , the starting current will be how many times greator than the current values if started in wye
3 times
69
when selecting a relay for a particular application, one must determine
coil voltage
#of contacts
contact rating
70
Most capacitive proximity detectors have a maximum sensing distance of
25 mm - 1inch
71
capacitive proximity detectors can sense the presence of
wood copper or brass
72
ultrasonic detectors emit a
high frequency sounds
73
Photodetectors with both transmitter and reciever require protection when unts are mounted in same housing
use reflector for operation
74
In canada, most 3 phase industrial motors operate on voltages ranging
208v or 600v
75
common control systems operate on
120 volts
76
conrol transformers are used to step down
600v or 208v down to 120v
77
when using a 240v/480v to 120v control transformer on a 240v line (lower voltage)
Both primary windings are connected in parrallel
78
when using a 240v/480v to 480v control transformer on a 240v line
(higher voltage)
Both primary windings are connected in series
79
which is not a methof of interlocking
thermal interlocking
80
A method by which starters are connected so that one cannot be started until the other is started is known as
sequence control
81
To protect people, machines and production processes a
lockable disconnect
82
which type of single phase induction motor cannot be used with a variable speed controller?
Motors with a centrifugal switch
83
Variable frequency motor controllers must have some method of
reducing the applied voltage to the stator as frequency is reduced
84
Most VFDs provide
low speeding torque
current limiting
automatic speed regulation
85
A device could be installed to input accurate current draw data to a VFD?
Current transformers
86
A device used to accuratley moniter the speed of a motor
Hall effect sensor
87
Ramping refers to
accelereation and deeceleration to control motor
88
In a VFD, the maximum speed of the motor is controlled by the
maximum hertz
89
In a addition to their primary function of providing speed control for c motors , most variable frequency drivees can also provide
low speed torque control
current limiting
automatic speed regulation
90
What device could be installed to input accurate current draw data to a vfd?
current transformers
91
a device that should be used to acccurately moniter the speed is
hall effect sensor
92
ramping refers to
acceleration and deacceleration control of a motor
93
Many transistor- controlled VFD now employ a special type of a transistor called
insulated bipolar transistor
94
Ina VFD, the -------- setiting controls the maximum speed of the motor
maximum hertz
