Electrical Test Flashcards
1
Q
Are single phase motors more efficient than three phase motors of comparable horsepowers?
A
No
2
Q
Most single phase motors fall in to what horsepower range?
A
1/4hp to 20hp
3
Q
Single phase split phase induction motors are classified by
A
the way the stator windings are used to starting and running
4
Q
What are the main components of the resistance split-phase motor? (4)
A
- frame, rotor, stator, end bells
5
Q
What does a centrifugal switch disconnect?
A
the start windings
6
Q
When does a centrifugal switch open?
A
at approximately 75% to 80% of the rated speed
7
Q
In order for the motor to start, the current in the start start winding must be
A
out of phases with the current in the main winding
8
Q
The two winding of an RSIR motor are electrically out of phases by
A
90 degrees for a two pole motor
9
Q
The RSIR motor centrifugal switch is connected
A
in series with the start winding
10
Q
The resistance split-phase induction motor has
A
low starting torque and high starting current
11
Q
A resistance split phase motor is reversible if
A
- the connections to the start winding are brought out of the connection box
12
Q
A CSIR motor has a _________ capacitor in __________ with the ___________ winding
A
start; series; start
13
Q
The starting torque of a capacitor-start motor compared to a resistance split-phase motor is
A
higher
14
Q
In a motor, the run capacitor improves
A
power factor
15
Q
In a motor, the start capacitor impoves
A
torque
16
Q
The starting current of a CSIR motor compared to a resistance split-phase motor is
A
lower
17
Q
How is the direction of rotation changed in a RSIR motor?
A
interchange the run winding leads OR interchange the the start winding leads but NOT BOTH
18
Q
The capacitor of a CSIR motor is rated for
A
short time duty and is connected in series with the start winding
19
Q
The phase displacement between the current of the start and main windings of a CSIR motor_______than that of a resistance split-phase motor
A
greater
20
Q
On the low-voltage connection of a split-phase, single-phase motor, the main windings are connected in
A
parallel
21
Q
A PSC motor utilizes a
A
low capacitance oil filled capacitor
22
Q
Can permanent-split capacitor motor have more than one speed?
A
yes
23
Q
A permanent-split capacitor motor
A
energizes the start and run winding when operating
24
Q
What additional components does a two-value capacitor motor have that a permanent-split capacitor motor does not have?
A
a start capacitor and a centrifugal switch
25
What are common names for a two-value capacitor motor?
Capacitor Start Capacitor Run and Dual Value Capacitor Motor
26
Is a two-value capacitor motor reversible?
yes
27
The two-value capacitor motor has ________ starting torque
high
28
The centrifugal switch used in a two-value capacitor motor
Disconnects the start capacitor
29
A dual voltage motor connected for high voltage would have which terminals connected?
T2 and T3 connected together
30
A CSCR compressor requires a
potential relay
31
A current relay has
N.O. contacts
32
A potential relay includes
high impedance coil
33
A potential relay includes a
high capacitance coil
34
Resistance is determined by
- material of device
- size of the device
- size of the wire
35
A resistive circuit phase angle and phase relationship is
0 degrees and peak at the same time
36
The SI unit for Torque is
Newton Meters
37
In a RSIR motor, the start winding is disconnected at
Approximately 75% of rated speed
38
A CSIR motor has________ capacitance than other motors
greater
39
A starting capacitor has greater capacitance than
the run capacitor
40
The horsepower rating of a motor is determined by
the speed and torque (HP=torque x speed divided by 7121)
41
In a PSC motor, the ________ is connected continuously
run capacitor
42
A shaded pole motor a _________ coil and ______ winding(s)
shading; 1
43
A capacitor is rated in
(micro) farads
44
The proper method to discharge a capacitor is to
connect a 20K ohm and 5 watt resistor across the terminals
45
To change the rotation direction in an RSIR motor
change only the run or the start terminals (NOT BOTH)
46
The run winding's are mounted deep into the
stator slots
47
One benefit of skewered rotor bars is
quieter operation
48
The purpose of the end bells is to (3)
- seal the motor
- hold the bearings
- support the shaft
49
The centrifugal switch has
N.C contacts and is mounted on the shaft
50
A dual voltage motor is connected for high voltage run winding connected
- in series
51
A dual voltage motor is connected for low voltage run windings connected in
parallel
52
On a CSCR motor, the potential relay disconnects the
start capacitor and start windings
53
On a dual voltage RSIR motor connected for low voltage, the start winding would be connected
in parellel
54
A current relay contains what type of contacts?
Normally Open contacts
55
A potential relay contains what type of contacts?
Normally Closed contacts
56
To change the state of the contacts, a current relay relies on
In rush current
57
What is the definition of Power Factor?
the ratio of comparing true power in watts and the apparent power in VA
58
The capacitance of a capacitor is determined by
the size of the conducting plates and the space between them
59
A CSIR motor has a ___ capacitor connected temporarily and a _____ switch connected in ______ with the ______ winding
start; centrifugal; series; start
60
A capacitor is connected in _____ with the ___ winding
series; start
61
Dual voltage start winding terminals are labeled
T5 T6 T7 and T8
62
What are the four types of split-phase motors
- CSIR
-RSIR
- PSC
- CSCR
63
What are the two main components of the a split-phase motor?
stator and the rotor
64
What are the three main components of a start or run capacitor?
- two conductor plates
- dielectric material
- container to hold the plates and dielectric material
65
What is the purpose of a shading coil in a shaded-pole motor?
delay the development of magnetic flux in the shaded part of the pole so that a rotating magnetic field is created
66
What are the three switches that remove the start winding from the electrical circuit once a split-phases motor has started
- centrifugal switch
- potential relay
- current relay
67
What is the difference between an RSIR motor and a shaded-pole motor?
- RSIS motor uses an electrical switch and shaded-pole has a shading coil on half of each pole
- shaded pole has a lower starting torque than the RSIR
- the shaded-pole motor uses and electrical switch to remove the start winding from the circuit once motor achieved its running speed
68
What are the advantages of a PSC motor? (2)
good speed control and low running current
69
What is the stator constructed of in all single-phase motors
quantity of stacked and laminated iron plates
70
Which motor uses a potential relay?
CSCR motor
71
Which motor uses a current relay?
RSIR and CSIR motors
72
How long does the start capacitor stay in the electrical circuit when the motor is initially energized?
2 to 3 seconds
73
Which motor has a rotor made of permanent magnets?
ECM rotor
74
What is a microfarad?
Unit of measurement for capacitance
75
What kind of a capacitor is typically rated at less than 50 microfarads?
the run capacitor
76
Which motor circuit is constantly energized?
ECM motor circuit
77
What type of current is applied to the control module of the ECM?
Alternating Current (AC)
78
Are the windings of an ECM constructed as a three-phase winding? (T/F)
true
79
What is the voltage rating of a potential relay coil?
the voltage rating is the peak of the measured cemf that is between the start and the common winding as the motor starts
80
Name three components in the electrical circuit of an RSIR motor
- start winding
- run winding
- centrifugal switch or current relay
81
Name four components in the electrical circuit of a CSIR motor
- start winding
- run winding
- start capacitor
- centrifugal switch or current relay
82
Name five components in the electrical circuit of a CSCR motor
- start winding
- run winding
- start capacitor
- run capacitor
- potential relay
83
Name three components in the electrical circuit of a PSC motor
- start winding
- run winding
- run capacitor
84
What are motor starters and compressor relays?
they are devices used to switch on and off electrical power necessary for the motor or compressor to operate
85
What is a manual starter?
a switch that requires human power to open and close the electrical switch
86
List the six components of a contractor?
- core
- coil or electromagnet
- contact springs
- contacts
- armature
- armature springs
87
What does a relay use to change the position of the switch contacts?
an electromagnet to change the position of the switch contacts
88
What happens to a magnetic coil when the coil voltage is too high?
the insulation on the coil wire breaks down because of the heat produced by the high current
89
Explain what happens to a magnetic coil when the coil voltage is too low
- the coil draws higher than rated current and can burn out
- contact positions do not change
- chattering of the contact can occur, cause arc damage to the contacts
90
What are the four basic types of relays
- plug in relays
- industrial control relays
- power relays
- enclosed control relays
91
What are the two basic components of a magnetic starter
- contactor
- overloads
92
What do seal-in or holding contactors do?
keep the operating coil energized after the momentary contact start button is released
93
What is a short circuit?
when the current of the circuit takes a path of lesser impedance than the circuit design
94
What is an overload?
a current that is somewhat above the normal rated value for that circuit
95
Name four types of overload protectors
- solder pot
- electronic overload
- magnetic overload
- bimetal (thermal) overloads
96
What does the armature do in a contractor?
- moveable metal component that is attracted to the magnetized core
- it provides mechanical action that changes the position of the contacts attached to it
97
Who approves electrical components in Canada?
Canadian Standards Association (CSA)
98
What is the importance of the term "service factor" to a motor?
its a rating system that indicates the degree to which the motor can withstand periods of overload without damage
99
Where is the internal thermal protection installed on a compressor
- used on hermetic and semi-hermetic compressors to protect the motor from overheating
- located and imbedded in or near the windings of the motor
100
What are two types of thermal overload protectors?
- solder pot/ melting alloy
- bimetallic strip
101
Are fuses overload protection devises?
no; they are over current protection devices
102
What are two types of plug or cartridge fuses available?
- instantaneous (non-time delay)
- time delay
103
Opposition to current flow
Resistance
104
Resistance is determined by (3)
- material of the device
- size of the device (cross sectional area or diameter)
- length of the wire
105
What is the phase angle and phase relationship in a resistive circuit?
0 degrees; current and voltage are in phase
106
What is the type of power converted in a resistive circuit?
true or real power
107
What is the symbol and unit for true or real power
p; watts
108
What is the power factor in a resistive circuit?
pf = 1
109
What is the physical properties of an inductive circuit?
a coiled wire develops a new property called Inductance
110
What is the symbol and unit for Inductance?
L; Henry (h)
111
What is Inductance determined by? (3)
- material of the core
- size of the core
- number of turns
112
What are the 3 oppositions to current flow in an inductive circuit?
- resistance
- inductive reactance
- impedance
113
What is the symbol and unit for inductive reactance? What is inductive reactance determined by?
xL; ohms; xL = 2𝝅FL
114
What is impedance, its symbol and unit?
impedance is total opposition to current flow; symbol is "z" and unit is ohms
115
Impedance is a combination of
resistance and inductive reactance
116
What is the phase angle and relationship for impedance?
1 to 89 degrees; current lags the voltage
117
For impedance, what is the type of power converted, its symbol and unit?
True or real power; P; watts
118
For impedance, what is the type of power not converted, its symbol and unit?
Reactive power (wasted power); qxL; var (volt reactive)
119
For impedance, what is the total power, its symbol and unit?
Apparent power (total power consumed); S; volt amps
120
What is the the power factor for Impedance?
true power ÷ apparent power (p÷s)
121
Power triangle ***think Pythagoras***
Apparent power (s) - hypotenuse side
true or real power (p) - horizontal side
reactive power (qxL) - vertical side
122
Impedance triangle ***think Pythagoras)
Impedance (z) - hypotenuse side
Resistance (r) - horizontal side
Inductive reactance (xL) - vertical side
123
How to find angle theta?
horizontal side ÷ hypotenuse + shift + COS Sign
124
How is the phase angle and torque related
the lower the phase angle, the more torque a motor will have
125
What is ohms law
Current is directly proportional to voltage and indirectly proportional to resistance
126
What is kirchoff's voltage law
voltage drop across a load must equal source voltage
127
What is electron theory
Current flow through the load is negative to positive and through the source is positive to negative
128
What is American WIre Gauge?
a sizing metric for copper wire; larger the # the smaller the diameter of the conductor
129
What is voltage
- electromotive force and is measured across two terminals
- comparison of amount of electron flow between two terminals
- voltage across a closed switch = 0volts
130
What is Kirchoff's Current Law
Current leaving a point must equal current entering that point
