Motors / Transformers Flashcards
Which type of breaking is used to bring a motor to a quick stop by phase reversal
Plugging
What does a rectifier do in a circuit
Converts Ac to Dc
What type of waveform is produced by half- wave rectifier
Pulsating DC
What would be done prior to opening the primary disconnect switch of a high voltage distribution transformer
Unload the secondary
How does a Triac dim an incandescent lamp?
Changing the circuit impedance
Which AC motor would be installed, if a motor with good variable speed qualities is required?
Wound rotor
How must a synchronous motor be started?
As an induction motor
Which device serves the same function as a synchronous condenser?
A bank of capacitors
Which device is used to test for short circuited coils in a motor?
Ohmmeter (key word test)
When does the blower fan operate during normal heating operation of a forced air gas furnace?
The fan comes on last and shuts off last
What best describes the comparison between a split phase resistance start motor and a capacitor start motor of the same size?
Different starting torque and the same running torque
What type of DC motor would be used for an application requiring extremely high starting torque if good speed regulation was not important?
Series
What is the function of a an automatic compensator used with a 3 phase motor?
Lowers the starting current
What is the function of the grease in the bearings of an electric motor?
Reduce heat from the mechanical friction
What type of single phase motor is used with domestic refrigerators?
Capacitor start
What is another term for Root mean square?
Effective value
What is the phase relationship between current and voltage in pure capacitive circuit?
Voltage lags current by 90 degrees
When an AC installation requires a motor having variable speed characteristics, what type of motor should be used?
Wound rotor induction motor
What conditions would cause a motor to burn out?
Excessive heat due to an overload
What is the main reason for lubricating bearings in a motor?
Reduce heating
What is the proper procedure to follow when energizing an oil filled transformer for the first time?
Open the secondary and energize the primary
What would you use to clean DC motor brushes?
Fine sandpaper
What does a megohmmeter measure?
Resistance
How is the primary of a current transformer connected?
Series with the load
What is a plugging switch?
Zero speed switch
What function do electrical interlocks provide for a reversing starter?
Prevent more than one coil from energizing at the same time
What is required for a single phase motor to operate on two voltages?
Two run windings
How does motor current compare, when dual voltage AC motor is operated on the higher voltage?
Decreases from lower voltage
What part of an AC to DC power supply keeps the output voltage constant with changing load?
Voltage regulator
Which switch type can only be used to separate the circuit from its source of supply but neither establish nor interrupt the flow of current
Isolating switch
Where are the overload relays for a size 1 magnetic starter physically placed?
At the contractor
Which of the following motor control circuits would provide low voltage release?
Two wire circuit with switch connected in series with the coil
What must be done when removing the meter from a metering circuit that uses a current transformer?
Short the secondary winding
What test instrument is used to determine the speed of rotating equipment?
Tachometer
How would an ammeter indicate that a motor had shorted coils in one phase?
Higher then normal current in one phase
How would an ammeter indicate that a motor had an overloaded condition
Higher than normal current in all three phases
An ungrounded 3 phase system has a ground detection lights installed. How would the ground detection lights indicate that none of the phases are grounded?
All three lights are on
What is the standard direction of rotation of a DC motor
Counterclockwise from the commutator end
Which DC motor should be directly coupled to its load
Series
How is the direction of any DC motor reversed?
Reverse polarity of armature field
Which DC motor must contain field loss protection?
Shunt
What is the maximum speed that the rotor of an induction motor will turn?
Rotates at synchronous speed minus slip
How do you reverse a shaded pole motor?
Take the motor apart and rotate the rotor shaft end from end
When asked to bump the motor what will the test indicate?
The direction of rotation
Which of the following is one disadvantage of an auto transformer?
There is no primary - secondary electrical isolation
What is the main purpose of bonding a motor frame to ground?
Limit the Voltage to ground
Which of the following factors influences the voltage regulation of an AC alternator?
Load and power factor
What is the term mechanical degrees referring to in a generator?
The revolution of the armature conductor
What is the purpose of reduced voltage starting for a motor?
Reduce the inrush current
What are the purpose of the auxiliary contacts on a motor starter?
They seal the coil in the energized state when the start button is pressed
Which of the following pairs of motor data determines the nema size starter for a motor?
Horse power and voltage
What does a VFD insert into the stator of an AC induction motor in order to achieve electric frictionless braking?
Direct current
What is the purpose of overload protection in a motor control circuit?
Protect the windings of the motor
Where should the overload protection device be installed in a motor branch circuit?
Between the motor control contractor and the motor
How is the direction of a single phase AC capacitor start induction - run motor reversed?
Reverse the connection of the start windings
When connecting two generators in parallel to supply an electrical system, what items must be synchronized?
Voltage and frequency
A DC motor obtains its supply from a bridge rectifier and a solid state starter. If one diode of the bridge rectifier opens, what happens to the motor if running under full load?
Motor would stall
What is the speed of the rotating magnetic field of an induction motor?
Synchronous speed
How would the shunt field windings of a cumulative compound motor be described?
Many turns of small wire
What can be used to correct armature reaction in a DC motor with varying load
Using interposes of the same polarity connected in series with the armature
The load requirements of a DC motor is do an extremely high starting torque. If speed regulation is not important, what type of motor should be used?
Series motor
Which device is used to test for unbalanced current in a feeder installation?
Ammeter
Which device is used to test for unbalanced current in a feeder installation?
Ammeter
What device is used to help prevent tracking and flashover in high voltage cables?
Skirts
How is the range of an analog ammeter increased?
Install a shunt in parallel
How is the range of an analog ammeter increased?
Install a shunt in parallel
What is the speed of the rotating magnetic field of an induction motor?
Synchronous speed
What two conditions could cause higher than normal nameplate full load current in a squirrel cage induction motor?
Low system voltage and excessive mechanical load
How will moisture in the oil of a liquid filled transformer affect it?
Bad dielectric
Which of the following DC motors would not be used for belt drive applications?
Series
What is the purpose of the shading coil in AC contractors?
Prevent chatter and AC hum
How are magnetic blow out coils connected in large DC starters?
In series with the load
How do you safely dry out a damp air cooled transformer?
Apply a small amount of voltage to primary under no load
What is the condition of a capacitor that has a reading of zero when tested with an ohmmeter?
Short circuited
What condition is indicated by an ohmmeter that registers infinity when testing across an overload heater?
Open
Which diagram shows the complete electrical distribution layout?
Single line diagram
What is the purpose of the shunt field relay in the DC motor control circuit?
Prevent dangerous acceleration
What will be the result if the contacts of the centrifugal switch in a single phase motor do not close due to malfunction of accumulation of dirt?
The run winding will be energized but the motor will not start
Which type of voltage are generally indicated by AC voltmeters?
RMS
Which of the following is not a common method of starting a polyphase squirrel cage induction motor?
Capacitive starting
Which of the following characteristics best describes a wound rotor motor?
High stating torque and low starting current
How is the range of a voltmeter increased?
Connecting a multiplier in series
What type of motor is considered a general purpose 3 phase AC motor?
Squirrel Cage
