Single phase motors and Transformers Flashcards
The motor that has a rotor that spins at the same speed as the magnetic field is the:
Shaded pole
Resistance split-phase induction
Synchronous
Permanent-split capacitor
Synchronous
The motor with the greatest starting torque is the:
Shaded pole
Resistance split-phase induction
Capacitor-start Induction
Permanent-split capacitor
Capacitor-start Induction
On a motor name plate, frame type refers to;
the manufacturers specifications & dimensions of this motor
model & serial number of the motor
the number of poles in the stator windings
this is a psychoanalytic term & does not refer to motors
the manufacturers specifications & dimensions of this motor
Why are motor rotors made of thin sheets of metal laminated together?
Lower manufacturing costs
Lighter weight
Better heat dissipation
It increases efficiency, by reducing Eddy Currents
It increases efficiency, by reducing Eddy Currents
Why do the maximum voltage ratings on capacitors rarely correspond with common line voltage? (ex. 340-volt rating for a 240-vac motor)
A safety factor is added in
To compensate for line loss
Capacitors are rated for peak voltage
Capacitors have no voltage rating
Capacitors are rated for peak voltage
How can you reverse the rotation of a shaded pole motor?
Remove the motor, and reinsert it into the stator at 180 degrees
Reverse the main electrical connections
Reverse the start capacitor
It can’t be done
Remove the motor, and reinsert it into the stator at 180 degrees
A primary resistance starter starts a motor with a resistance __ _____ with the main motor windings.
in parallel
in conjunction
in proximity
in series
in parallel
The term “Class 2 Transformer” is defined in;
Section 16 of the Canadian Electrical Code
Modern Refrigeration
Book of the Dead
ASHRAE
Section 16 of the Canadian Electrical Code
Of the motors listed, which has the largest horsepower rating?
Capacitor-start Induction
Resistance Split-phase Induction
Universal
Shaded pole
Capacitor-start Induction
NEMA is an acronym for……
National Electronic Manufacturers Association
Nashville Election Makers Affiliation
Neutered and Emasculated Mammals Action Committee
National Electrical Manufacturers Association
National Electrical Manufacturers Association
What are the two types of bearings used in most motors?
Slip bearings and ball bearings
Needle bearings and roller bearings
Sleeve bearings and ball bearings
Roller bearings and slip bearings
Sleeve bearings and ball bearings
How many electrical degrees apart are the start and run windings on a permanent-split capacitor motor?
15-45 degrees
25-75 degrees
30-40 degrees
80-90 degrees
80-90 degrees
From the list below, select the motor with the greatest starting torque:
Shaded pole
Universal
Resistance Split-phase Induction
Permanent-split Capacitor
Universal
On a capacitor-start induction motor the angular phase displacement is created by:
The Run Capacitor
Centrifugal Switch
The Start Capacitor
Resistor in series with the windings
The Start Capacitor
A centrifugal starting switch is designed to open at approximately _______ of full load current.
65-70%
70-75%
85-90%
95-100%
70-75%
How are the start windings connected on a 120/240-volt single phase motor, when the motor is connected to lower voltage?
Series / parallel
Parallel
Series
None of the Above
Parallel
How is the direction of rotation of a motor determined?
Viewing the motor from the front
Viewing the motor from the back
Viewing the motor from lead end
Viewing the motor from opposite sides
Viewing the motor from lead end
How is the rotation of a resistance-start induction motor normally reversed?
Reverse the start winding connections.
Reverse the run winding connections.
Physically flip the motor 180 degrees.
Switch the connections on the start capacitor.
Reverse the start winding connections.
Which document describes the rules by which a gasfitter may do work?
B149.1
B149.2
B149.3
All the above
All of the above
What would the total capacitance be for three 30 µF capacitors connected in parallel?
10 µF
30 µF
90 µF
You can’t do that!!!!
90 µF
What type of single-phase motor does not require a starting switch?
None do
Permanent-split capacitor
Resistance split-phase induction
Universal
Capacitor-start induction
Permanent-split capacitor
The name plate on a 60 Hz single phase motor is 850 rpm. The motor must have:
two poles
four poles
six poles
eight poles
eight poles
Which of the following is most likely a start capacitor?
145 µF, electrolytic (oil filled)
90 µF, dielectric (dry)
25 µF, dielectric (dry)
7.5 µF, electrolytic (oil filled)
90 µF, dielectric (dry)
A motor can be installed in an explosive atmosphere as long as it is of a fully enclosed type.
True False
False
On a motor name plate, ID number refers to;
Frame Type of motor
Model & Serial Number of the motor
The number of poles in the stator windings
This is a psychoanalytic term & does not refer to motors
Model & Serial Number of the motor
What is the purpose of the Safety Codes Act?
To protect the occupants and users of a building.
To provide public safety
It makes it mandatory to pull a permit on every job
It states that a gasfitter can work on equipment over 400,000 BTU’s
To provide public safety
What amount of current causes ventricular fibrillation of the heart?
100 to 200 mA
15 A
15 to 20 mA
over 200 mA
100 to 200 mA
The capacitor of a capacitor-start motor is rated for:
short-time duty and is connected in series with the auxiliary winding
continuous duty and is connected in parallel with the auxiliary winding
continuous duty and is connected in series with the auxiliary winding
short-time duty and is connected in parallel with the auxiliary winding
short-time duty and is connected in series with the auxiliary winding
When there is a comparable motor size and load, what is the starting torque of a capacitor-start motor compared to a resistance split-phase motor?
higher
lower
the same
dependent upon the load
higher
Single-phase motors are more efficient than three-phase motors of comparable horsepower.
True False
False
Which testing device listed below is used to verify the motor insulation integrity?
Amp meter
Megger
Ohm meter
Frogger
Megger
What are two ways a transformer may be short circuited?
overheating, overloading
accidental contact of terminals, overuse
cycling of controls, using wires which are too large
wiring heating controls in improper sequence, short circuiting a gas valve to check its operation
overheating, overloading
What do manufacturers recommend as a maximum loading factor of the devices that are connected to the secondary side of a dry transformer used for controls?
100 %
48 VA
2 amps
80 %
80 %
What is the purpose of laminating the core of a dry transformer?
It allows smaller sections of material to be used.
It makes the transformer less expensive to manufacture.
It keeps eddy losses to a minimum.
It strengthens the core.
It keeps eddy losses to a minimum.
How are the laminations of a transformer core kept electrically separate from each other?
varnishing each section or place paper between the layers and varnish the sections.
place plastic strips between them.
laminations are not electrically separated.
place laminate between the individual core sections.
varnishing each section or place paper between the layers and varnish the sections.
Which of the following conditions is most likely to be the cause of primary windings opening in a step-down transformer?
high current flow in the secondary windings
high voltage supplied to the primary windings
AC transformer is connected to DC supply source
transformer rated as type F is used in a type A heat environment
high current flow in the secondary windings
A 14 AWG stranded wire can carry more current than a 14 AWG solid wire.
True False
False
The voltage supplied to a circuit is 24 volts, what is the amperage if the resistance draw of the circuit is 80 ohms?
0.03 amps
0.3 amps
3 amps
3.33 amps
0.3 amps
A=v/r
What do manufacturers recommend as a maximum loading factor of the devices that are connected to the secondary side of a dry transformer used for controls?
100 %
48 VA
2 amps
80 %
80%
Assume a high limit is connected to line voltage. If the limit opens, what voltage will be read ACROSS the control?
24 VAC
120 VAC
12 VDC
0 VAC
120 VAC
A Transformers maybe AC or DC!
True if rated for 30 volts or less.
True if rated for 24 volts or less.
Yes it may be DC
AC only
AC only
Why is it important to zero an analog meter each time you are going to make a resistance reading?
This procedure ensures the meter will be starting from zero for each resistance scale.
This check establishes the condition of the meter’s internal batteries.
This check establishes zero electrical flow in the circuit.
Zeroing the meter allows you to ensure the meter is working properly.
This check establishes the condition of the meter’s internal batteries.
Static charges accumulate on insulator material!
True False
True
What is the maximum voltage unbalance allowable?
2%
5%
10%
12%
10%
What is reactive power in relation to the output of a transformer?
The transformer reacts to the power load placed on it.
The transformer reacts to the thermostat.
Power is used to create an electromagnetic field
Power causes a direct reaction such as turning on a switch starts an electric motor.
Power is used to create an electromagnetic field
According to the law of Repulsion and Attraction;
Unlike poles repel and like poles attract.
Like poles repel and unlike pole attract.
Like poles repel and unlike pole attract.
What is the maximum permissible amperage draw of the secondary side of a transformer with 24-volt output and a 80 VA rating?
0.133 A
1.33 A
0.33 A
3.33 A
3.33 A
AD = VA / V
Determine the load voltage if the primary coil has 120 Volts with 240 turns and the secondary has 1200 turns?
24 Volts
120 Volts
1200 Volts
600 Volts
600 volts
When looking at a transformer from the low-voltage side, the standard H1 terminal position is located at:
the upper right-hand corner
the lower right-hand corner
the upper left-hand corner
the lower left-hand corner
the upper left-hand corner
What are control transformers sized to?
supply voltage
load voltage
load current
VA/kVA rating
VA/kVA rating
What design feature of a current limiting transformer prevents any increase in secondary current when core saturation is near its peak?
High resistance secondary coil
Air gap
Laminated core
None of the above
Air gap
Which of the transformer designs listed below has the least amount of flux leakage?
Core Type
H Type
Shell type
U type
H type
