MARE-306 Lab Test 2
One major advantage of a separately-excited shunt motor is that the motor can be operated __________ its rated nameplate speed.
above
Anytime a motor can be operated on different voltages, it is better to select the high voltage confi guration because the motor will draw less ________.
amperage
Three-phase induction motors ________ (are/are not) the most effi cient type of electric motors available next to synchronous motors.
are
The __________ windings have much less resistance than the field windings.
armature (one)
The only sure method to reverse the direction of rotation on a cumulative compound motor is to reverse the __________ connections.
armature (three)
The direction of rotation on a DC shunt motor can be reversed by either reversing the field connections or the ___________ connections.
armature (two)
The maximum speed of a self-excited shunt motor is determined by the __________.
armature current
The process of reducing the field current of a separately-excited shunt motor is called __________.
field weakening
A three-phase induction motor has a _______ (high/low) power factor.
high (one)
If the phase halves are connected in series on a three-phase motor, the motor is confi gured for ______ (high/low) voltage operation.
high (two)
A DC compound motor provides ________ (higher/lower) starting torque than a shunt motor.
higher (three)
The windings on a three-phase motor are __________ (identical/different).
identical
When a DC motor is connected in the separately-excited configuration, as the field current is decreased, the motor speed ____________ (increases/decreases).
increases
The two most common categories of three-phase motors are synchronous and ____________.
induction (one)
About 95% of the motors used in industry are __________ motors.
induction (two)
If the winding halves of a dual-voltage delta motor are connected in parallel, the motor is wired for __________ operation.
low voltage
Some times, the three phases in a three-phase motor are divided in half to allow ______________ operation.
low/high voltage
Most _______________ use three-phase induction motors because of their effi ciency and easy speed control through gear of belt drive systems.
machine tools
In many cases, the switching of lines to reverse a three-phase motor is accomplished through two sets of _____________.
magnetic contacts
An advantage of a self-excited DC shunt motor is that it is able to ___________ its speed over a wide load range.
maintain
Devices used to switch the lines to a three-phase motor often include built-in safety __________ to prevent phase-to-phase shorts.
measures
How do you calculate Slip?
((Synchronous Speed RPM - Actual Speed RPM)/Synchronous Speed RPM)*100
How to calcualte kW (S.I units)
(Torque (N-m) *Speed (RPM))/ 9549
How to claculate Hp (U.S units)
(Torque (ft-lb) *Speed (RPM))/ 5252
A DC compound motor provides better _______ control than a series motor.
speed
Large conveyor systems rely on the good _______________ of the three-phase induction motor to provide constant speed even if the load changes.
speed regulation
Two common types of induction motors are ______________ and wound rotor.
squirrel cage
The square root of 3 is __________.
1.73 (one)
For a 3-phase circuit, the product of the line voltage and current must be multiplied by __________.
1.73 (two)
A three-phase motor usually has a service life of _____ years or better.
10
Each phase in a 3-phase circuit is __________ electrical degrees apart.
120
By switching ______ of the supply lines to a three-phase motor you can reverse the direction of rotation.
2
The average range of slip for squirrel-cage induction motors is 2% to ____%.
6%
How to calculate efficiency
Efficiency = (Power Out/ True Power) *100
The industry standard method for reversing a three-phase motor is to switch lines L1 and ___.
L3
How do you calculate Apparent Power in 3-phase circuit?
P(a) = V(line) * I(line) *1.73
How do you calculate Power Factor?
Power Factor = True Power / Apparent Power
A DC __________ motor is a motor with a field connected in both series and in shunt with the armature.
compound
If the series and shunt windings in a compound motor are connected so that their magnetic fields have the same polarity, the motor is configured as a __________ compound motor.
cumulative
In a ________ confi gured three-phase motor, the phase windings are connected end-to-end to form a closed loop.
delta
The __________ compound motor has very few applications and is avoided for the most part.
differential
A DC shunt motor ________ (does/does not) provide high starting torque.
does not
A DC shunt motor has its fi eld windings connected in ________ with the armature.
parallel
The two sets of contacts used to reverse a three-phase motor are often controlled using __________, one for forward and one for reverse.
pushbuttons
A DC shunt motor will not __________ if there is no load connected to it, unlike a DC series motor.
run away
When the shunt field is connected to the same power supply as the armature, it is called a _______________ shunt field.
self-excited
When a separate power supply is used for the shunt field, it is called a _____________ shunt field.
separately-excited
The input current on each line to a three-phase motor should be ___________ (the same/different).
the same
The _______ three-phase distribution system is the safest of the two systems.
wye (one)
Two wiring confi gurations for a three-phase motor are the _____ and delta confi gurations.
wye (two)