Dc Motors Test
What 3 things do a Brushless DC motor NOT contain?
A wound armature, commutator or brushes
used more than any other type of DC motor in industry
Compound Motor
opposite polarity voltage induced into armature as it spins through magnetic fields of pole pieces.
Counter-electromotive
Series aiding magnetic field windings
Cumulative Compound Motor
What is the principle of operation of a dc motor?
Dc motors opperate on the principle of attraction and repulsion of magnetism
The compound motor connection that should generally be avoided is the _____.
Differential
Permanent magnet motors have _____ efficiency than conventional field-wound motors.
Higher
Pushing or turning force
Torque
The pushing or turning force created by the magnetic field of the pole pieces and the magnetic field of the loop or armature is called
Torque
Very good speed characteristics
Shunt Motor
Referred to as constant speed motors
Shunt Motor
Dc series motors are generally used where
A constant torque was needed
The speed regulation of a DC motor is proportional to the _____.
Armature Resistance
In a compound DC motor control circuit, the field loss relay will disconnect the _____ if power is lost to the _____.
Armature, Shunt field
The motor that does not contain a wound armature, commutator, or brushes is the _____ motor.
Brushless Dc
does not contain a wound armature
Brushless Dc Motor
When a DC machine is used as a motor, the _______________ performs the function of a rotatory switch and maintains the correct direction of current flow through the armature windings.
Commutator
Uses both series and shunt field windings
Compound Motor
Series opposing magnetic field windings
Differential Compound
In general, what type of compound motor connection should be avoided?
Differential compound connection
A device that converts electrical energy into mechanical energy is called a(n)
Motor
Device used to convert electrical energy into mechanical energy
Motor
Does not need shunt fields or series field windings
Permanent Magnet Motor
pole pieces of motor need no excitation to become magnets
Permanent Magnet Motor
Dc compound motors are used to drive machines that require a
Relatively constant speed under varying loads
What is the most common way of changing the direction of rotation of a compound motor?
Reverse the connection of the armature leads
Speed is controlled by the amount of load connected to the armature
Series Motor
The best torque characteristics
Series Motor
What type of motor should never operate with no load?
Series Motor
The amount by which the speed decrease as load increases
Speed regulation
What 3 factors determine the amount of Cemf produced in the armature?
The speed of the armature The number of turns of wire in the armature The strength of the magnetic field of the pole pieces
What 2 factors determine the amount of torque developed by a DC motor?
The strength of the magnetic field in the pole pieces The strength of the magnetic field in the armature
When does a motor operate at base speed?
When full voltage is applied to both the armature and shunt field
How can a DC motor be made to operate above base speed?
When full voltage is applied to the armature and reduced voltage is applied to the shunt field
What limits the amount of current flow through the armature when power is first applied to the motor?
Wire resistance in the windings of the armature
Dc shunt motors should never be operated...
With the field circuit open
no natural speed limits and never operated with no load condition
Series Motor
Functions to disconnect power to the armature if shunt field current decreases below a certain level
Field-Loss Relay
Field windings are connected in parallel with armature windings and are the only set of windings
Shunt Motor
When a motor is connected differential compound, the _____ determines the direction of rotation of the motor at no load or light load.
Shunt field
Counter-electromotive force (CEMF) and back-EMF are names for the voltage induced into the armature of a DC motor.
True
A compound motor has _____ field windings.
Series and Shunt
Small permanent magnet motors that have lightweight rotors are often used as _____.
Servomotors
A series motor may be operated with no load connected.
False
The DC motor, known as a "constant speed motor," is the _____ motor.
Shunt
When the field winding of a DC motor is connected in parallel with the armature, the motor is called a _____ motor.
Shunt