Flashcards in ILT166 Deck (48):
What is the purpose of a commutator on a DC motor?
To maintain the proper direction of current flow to the armature conductors
What three things does an electric motor require?
External source voltage, a magnetic field, and a conductor
What is torque?
The turning force produced by a rotor
What are the two basic categories of electric motors?
AC and DC
An electric motor uses _____ and _____ to operate
Electric current, Magnetism
On a 3 phase AC motor, the stator windings are arranged to create _____
a rotating magnetic field
DC compound motors are used to operate loads that require _____
Low starting torque
A DC shunt motor should never be operated with _____
The field circuit open
What will happen if the field current of a shunt-type DC motor is held constant and the armature voltage is increased?
The speed of the motor will increase
The direction of rotation of a shunt wound DC motor is change by reversing the _____, not the _____
Current flow, Field
A shunt type DC motor is known to have a _____
High starting torque
The direction of rotation in a 3-phase induction motor is determined by the _____
What happens when a load is applied to a 3-phase squirrel cage induction motor?
The rotor speed will decrease slightly
What is the synchronous speed of an induction motor?
The speed of the rotating magnetic field
When dual-voltage, 9 lead wye-connected, 3-phase motor is connected for high voltage are the coils connected in series or parallel?
As the load on an induction motor increases the power factor will _____
How can the speed of a squirrel cage motor be varied?
By varying the supplied frequency
A variable A/C motor drive delivers _____ and _____
Fixed line voltage, variable frequency
A permanent capacity motor does not require a _____
Which motor has the highest starting torque of all the single phase motors?
A capacitor start/ capacitor run motor
A wound rotor induction motor is normally started with _____
DC voltage applied to the rotor
Current flow through the windings of a transformer can generate _____
What is impedance matching?
adjusting the impedance to produce the desired energy transfer
What happens to current in a step-up transformer?
It is stepped down
What is the turns ratio?
The ratio of the number of turns in the secondary winding to the number of turns in the primary winding
When a transformer is connected to a pure inductive-resistive-capacitive load, the circuit is purely _____
resistive at resonance
When is a transformer likely to overheat?
When the transformer is operating above its secondary voltage
What must be known to calculate the power rating of a transformer?
Voltage and current ratings
How can you reduce the cost of power lines?
Reducing current and increasing voltage
What are the two sets of windings in most transformers?
Primary and secondary
Why are induced currents bad in an iron core?
They produce heat and use power
Transformer efficiency is the ratio of _____ to _____
output current to input current
What determines a transformer's classification?
Its operating frequency
What is one advantage of an autotransformer?
Current flow through the windings is reduced
What do buck and boost transformers do?
Either raise or lower line voltage
In an AC transformer, currents lag their respective voltages by _____ degrees
What is an isolation transformer used for?
Electrically separating the source voltage and the load
What is a transformer?
An electrical device that uses magnetism to change voltage from one level to another or isolate one voltage from another
What is flux loss?
Power loss in a transformer caused by resistance of the copper windings
What is eddy current loss?
Power loss due to currents induced in the metal structure from the magnetic field
What is the standard frequency for power distribution in North America?
What is a core type transformer?
A transformer with windings placed around each leg of the core
What letter represents the secondary winding leads?
What unit are AC transformers rated with?
What is an autotransformer used for?
To raise and lower voltage as required by the circuit
Do current ratings specify the primary or secondary windings?
What is the turns ratio?
The number of flux lines linking the primary and secondary transformer windings