Motor Controllers Flashcards
What are the two general methods of starting motors electromagnetically
Manually and automatically
By what means are the contractors of a magnetic controller operated
Electromechanical devices
Remote control master switch
By a locally controlled master switch
What type of controller is used to start a 1/4hp-dc motor
A dc across the line motor controller
What type of controller is used to insert resistance in the secondary circuit of a wound rotor motor
An ac secondary resistor
What is the major advantage of the closed transition transformer I’ve r the open transition transformer
The motor can’t slip out of phase during the transition phase
Which of the following is a disadvantage of an open transition compensator
The motor may slip out of phase during transition, causing an overload
By what means is the designation of a magnetic controller shown?
Numerically, according to the max horsepower rating of the connected load
What type of controller enclosure provides the least amount of ventilation to the internal components
Submersible
If a master switch is mounted in the controller it is classified as what type of switch
Local
What is the purpose of arcing contacts
To reduce the amount of arcing at the main contacts when opening or closing
What method of any should you use to keep arcing contacts clean
None; they are self cleaning
By what means do magnetic blowout coils quench the arc across contacts
By providing a magnetic flux that blows out the arc
When the energized contacts in an ac contractor are opened, what method is used to quench the arc that is created
An air gal dissipates the arc
What factor allows ac contractor coils to be smaller than dc coils rated for the same voltage
Inductive reactance causes counter emf to limit current flow in an ac coil
A controller protecting a motor is able to disconnect it from the power supply, keep it disconnected, and then restart it automatically when conditions return to normal. Which of the following forms of protection is the controller providing
Low-voltage release
Shunt contractors will handle ul to what (a) current at what (b) voltage
600A
230V
What material is used to construct the arcing contacts of a dc controller
Copper with a heavy coating of cadmium
What is the major difference between an LVR and an LVRE controller
The LVRE does not use a coil in its circuit to operate the contacts
You are installing a new 450-volt, three phase motor controller according to a ship alteration. If the motor is rated at 15hp, you should use what size controller?
2
What means is used to determine the speed of ac squirrel cage induction motors?
The speed of the rotating magnetic field
What means should you use to change the speed of an ac motor through the controller?
Chang edge connections to the motor
One type of a motor speed controller controls the speed of the ac motor by performing which of the following actions?
Switching from one set of stator windings to another
What means is used to determine the speed of dc motors
The amount of current flowing through
A reversing type of controller protects a three phase induction motor again ash low voltage and overload by causing the motor to stop running due to line voltage failure. After line voltage is restored, what action, if any, should you perform to restart the motor?
Press the forward or reverse bush buttons
What is the most common method used to reverse the direction of rotation of a dc motor through a controller?
Reversing the connection of the armature with respect to the field
Three phase auto transformers are used to start three-phase induction motors and synchronous motors because they have the ability to perform what function?
Furnish variable voltage
By tapping an auto transformer, it is possible to obtain a voltage higher than the source voltage
False
What is the most common application of logic controllers aboard ship?
Elevator control
Logic devices and controller have what advantage over standard electrical components?
They have a quicker response.
They don’t have any moving parts
They consume less power
In a magnetic circuit breaker, what circuit is opened by an overlay relay
The operating coil of the main contractor
What is a coarse adjustment to the thermal overload relay?
Changing the heater element
The tripling current of magnetic overload relays must be set higher than the starting current of the motor they serve
True
What is not considered a thermal overload relay
Dashpot
A heat sensitive element that lengthens when heated to open the contacts is used in what type of thermal overload relay
Single metal
What type of thermal overload relay is manufactures for exclusive use in ac circuits
Induction
In relation to the starting current of the motor they serve, the tripling current of the magnetic overload relay must be set in what way
Higher then the starting current
In the instantaneous and time-delay magnetic overload relays, you should use what method to adjust the current settings?
Change the distance between the induction coil and the tube
Which of the following types of overload relays require a time delay before it is reset
Solder pot
Symptom:
Over head contact tips
Insufficient tip pressure
Symptom:
Short contact life
Excessive jogging
Symptom:
Coil failure (not overheated)
Mechanically damaged
