Motor Controls Final Exam
True
If the current flow through the shunt field is interrupted, a compound wound, DC motor will become a series motor and race to high speeds.
False
If the load is added to a motor, the motor speed increases.
True
Many autotransformer starters contains taps that can be set for 50, 65, or 80 percent of the line voltage.
False
Mechanical type brakes cannot hold a suspended load.
False
Open transition starting means that the motor is connected to the power line during the transition from wye to delta.
True
Synchronous motors are able to operate at the speed of the rotating magnetic field because they are not induction motors.
True
If the winding is such that the series delta gives the low speed and the parallel wye gives the high speed, the torque will be the same for both speeds.
False
In a resistive circuit, the current will take some time to reach its full Ohm's law value.
False
In a wye connection, the line current and phase current are not the same.
True
In an inductive circuit, the current must rise at an exponential rate.
True
In order to produce a rotating magnetic field, there must be more than one phase.
True
In part winding starting, neither of the two windings is individually capable of withstanding the starting current for more than a few seconds.
True
Inverter rated motors are specifically designed to be operated by variable frequency drives.
False
It is possible to troubleshoot a circuit without a working knowledge of schematics.
True
Most autotransformer starters use two transformers to reduce the voltage applied to the motor during the period of acceleration.
True
Most motor circuits are protected by dual-element time delay fuses or inverse time circuit breakers.
True
Motors that used a centrifugal switch to disconnect the start windings cannot be used with variable voltage control.
False
Multiple speeds are obtained by connecting inductance in parallel with the main run winding.
True
One method of providing plugging control is with the use of an automatic timed circuit.
True
One of the factors that must be taken into consideration when determining the conductor size is the temperature rating of the devices and terminals.
True
One way of determining when to shunt the resistors out of the circuit is by sensing the motor current.
True
Overload relays are intended to disconnect the motor from the power line in the event that the current draw becomes excessive.
True
Part winding starters provide closed transition starting.
True
Part winding starting is typically used for motors that supply the moving force for centrifugal pumps, fans, and blowers.
False
Plugging is used with direct current motors more than with three phase squirrel cage motors.
False
Plunger type voltage testers can be used to test control systems that operate on low voltage, such as 24 volt systems.
True
Ramping permits the motor to bring the load up to speed slowly as opposed to simply connecting the motor directly to the line.
True
Resistors connected in series with the motor limit the amount of in-rush current.
False
Series field windings are marked F1 and F2 in the terminal connection box.
True
Shaded pole motors are used in applications where it is necessary to reverse the direction of rotation of the motor.
True
Shunt field windings exhibit a much higher resistance than the series field windings.
True
Small wound rotor motors are often controlled manually by a three-pole make-before-break rotary switch.
True
Starting circuits generally employ resistors of a lower wattage value than circuits that are intended for speed control.
False
Table 430.250 is used to determine the full load current of two phase motors
False
The Insulated Gate Biolar Transistor (IGBT) is a current controlled device, not a voltage controlled device.
True
The NEC tables list the amount of the current that the motor is expected to draw under a full load condition.
False
The amortisseur winding provides good starting torque and a relatively high starting current.
False
The armature of a large DC motor has high resistance.
True
The excitation current should be connected to the rotor only after it has accelerated to a speed that is close to synchronous speed.
True
The hot-wire relay functions as both a starting relay and an overload relay.
True
The magnetic field travels through the same number of poles during each complete cycle.
False
The problem with eddy current clutch circuits is that they lack a speed sensing device that automatically increases or decreases the DC excitation current when the load is added or removed.
True
The shunt field power supply is generally designed to remain turned on even when the main (armature) power supply is turned off.
True
The type of bars used to construct the rotor has a great effect on the operating characteristics of the motor.
False
The values listed in Table 430.248 are for motors that operate under high speeds and torques.
True
The wound rotor motor can be started in multiple steps to provide smooth acceleration from 0 RPM to maximum RPM.
False
The wound rotor motor has a lower starting torque per amp of starting current than any other type of three phase motor.
True
Three-speed consequent pole motors can be wound to produce constant horsepower, constant torque, or variable torque.
True
When deenergizing or energizing a control cabinet of motor control center module, the electrician should be dressed in flame retardant clothing while wearing safety glasses, a face shield, and hard hat.
False
When dual voltage motors are used, the motor must be operated on the high voltage setting of the motor.
False
When using an ohmmeter, make certain that the power is connected to the circuit.
False
Wound rotor type motors and synchronous motors generally use autotransformer starters.
False
Capacitive reactance is proportional to the rotor frequency.
False
Centrifugal switches can be used on all types of split phase motors.
True
Changing frequency causes a corresponding change in the inductive reactance of the windings.
True
Closed transition starting does not disconnect the motor from the power line.
False
Clutches cannot provide a smooth start for loads that can be damaged by sudden starting, or for high inertia loads such as centrifuges or flywheels.
True
Compound motors contain both a series and shunt field.
True
Compound motors generally employ a field loss relay (FLR) that is intended to disconnect the motor from the power line in the event that shunt field current should be interrupted or drop below an acceptable level.
True
Contactors intended to connect direct current motors to the line often have arc suppression and magnetic blowout coils.
False
Delta connected dual voltage motors are acceptable for part winding starting.
False
Direct current motors depend on inductive reactance to limit current flow.
True
Double-face clutches have both the armature and field discs mounted on the same hub.
True
Dual voltage motors designed for wye-delta starting will supply all 12 T leads at the terminal connection box.
True
Dual voltage motors not intended for wye-delta connection will have certain terminals tied internally.
True
Dynamic braking for a DC motor is very effective, but the braking effect becomes weaker as the armature slows down.
False
For closed transition starting, four separate start contactors are used.
False
Frogleg wound armatures are most often used in small machines.
True
A DC motor is generally operated at or below normal speed.
False
A synchronous motor can not be made to produce a leading power factor.
True
A synchronous motor should never be started with excitation applied to the rotor.
False
A three phase, two-pole motor contains eight actual poles.
False
Across-the-line starting is only used for alternating current.
True
Across-the-line starting is the simplest of all starting methods.
False
Alternators are often used to control the speed of several induction motors that require different changes in speed.
True
Autotransformer starters provide greater starting torque per ampere drawn from the line than any other type of reduced voltage starter.
