Motor control
If the service factor for a motor is not give, what should you assume the service factor to be?
1
Three phase power is transmitted in phases that are _____ degrees apart
120
Which of the following is not a common voltage supply by a wye-configured system?
240?
A hand-off automatic (HOA) circuit requires a selector switch with________ positions
3
What would be the volts per Hertz ratio of a motor with a voltage rating of 240 VAC and a base operating frequency of 60 Hz
4 V/H
The frequency of the sine wave available for power companies in the US is
60 Hz
What should be the minimum frequency setting be for a 2 pole motor with a 60 Hz rating?
75 Hz
Which of the following is not a disadvantage of starting a motor with an AC drive instead of line starting?
AC drives always require three phase motor
Which of the following is an advantage if starting a motor with an AC drive instead of line starting?
All of the Above
Which of the following is not a basic rule of electrical safety?
Always work by yourself
Which of the following is not an advantage of using an AC drive instead of a DC drive?
An AC drive and motor can provide better starting torque than an equivalent DC drive an motor
A grounded neutral wire can be used as an equipment ground
False
A motor starter is the same as a motor controller
False
A time delay fuse only has one element
False
A variable frequency AC drive requires extra external circuitry to produce the DC voltage for DC injection braking
False
An average 2 pole industrial motor can be safely operated up to 200 percent of its base speed
False
Bimetallic overloads do not allow you to adjust the trip point
False
Low speed boost changes the volts per hertz ratio at all frequencies
False
Many variable frequency AC drives provide low speed boost to increase the voltage at low frequencies
False
Most variable frequency AC drives will not allow you to use manual inputs to jog a motor
False
Most variable frequency drives do not allow you to skip frequencies that put stress on a motor
False
One application of interlocking is the cause of the forward and reverse coil of a reversing contractor to be energized at the same time
False
Reflected wave voltage reduces the voltage that the motor recieves
False
S-curve acceleration/deceleration allows a slower acceleration rate a faster deceleration rather than regular ramping
False
The ramp up time and the ramp down time for a variable frequency drive must always be the same
False
To avoid running separate lines to a machine for power devices and control devices, the higher voltage required by the power devices can be produced by using a control transformer to step up the control
False
To get a control voltage of 120 VAC from a control transmitter if the voltage is 240 VAC, the primaries must be connected in series
False
When a control transformer is used, NEC requires both sides of the secondary must be connected to earth ground
False
Which of the following is not a result of connecting a dual- voltage motor to operate on the higher-voltage?
Increase current draw
Which of the following is not a step to reduce the effects of reflected wave voltage
Increase the PWM frequency
Based on the wiring diagram shown, which of the following statements is true of a drum switch if the switch is placed in the reverse
L1-T2,L2-T2,L3-T1
The__________ is the accepted standard in the US for safety installing and maintaining electrical systems and equipment
NEC
Who should remove a lockout/tagout
Only the person who installed it
Many variable frequency AC drives produce________ output
Pulse Width Modulation(PWM)
Which of the following us a factor that must be considered when selecting overcurrent protection devices for a motor control circuit?
Rated full load current of the motor
Which of the following items on a motor's nameplate us used to determine how much output power a motor can safely produce above its rated output power?
Service Factor
A magnetic overload includes a dashpot which allows adjustments to the response line of the overload
True
A reversing magnetic motor starter provides a magnetic method of changing a motor's direction of rotation
True
Certain frequencies from a variable frequency drive can cause a motor to run rough or vibrate
True
DC injection causes the motor to come to an immediate stop
True
Fly wheels often require S-curve acceleration/deceleration instead of straight ramping
True
If you are driving a high inertia load, the load may continue to rotate even though the ramp down time has expired
True
Magnetic contractors open and close their contacts through the use of a magnetic coil
True
Many variable frequency AC drives can be programmed so that different speeds can be selected by changing certain inputs or parameters
True
Mechanical interlocking should be used in combination with one if the electrical methods so that the blocked coil cannot be energized
True
Most variable frequency AC drives will allow you to control the direction and speed of jogging, as well as how quickly the motor will stop when jogging is stopped
True
NEMA overloads often use melting alloy thermal overloads
True
One problem with pulse width modulation is that each pulse begins with a spike that is nearly double the base voltage of the motor
True
The NEC requires that for an input voltage higher than 50 VAC one side of a control transformer secondary to connected to ground or both sides of the secondary must be fused
True
To get a control voltage of 120 VAC from a control transformer if the line voltage is 480 VAC, the primaries must be connected in series
True
Transformers are related in units called Volts Amperes(VA)
True
You can reverse the rotation of any three phase motor by interchanging any two of the three power supply lines
True
Parts of an electrical system that should be connected to earth ground include
all of the above
When checking a transformer with an ohmmeter, which of the following can you check for?
all of the above
Which of the following is a basic requirement for a typical motor installation?
all of the above
Which of the following is a common device that an AC drive can receive input from?
all of the above
Which of the following is a component of a reversing magnetic motor starter
all of the above
Which of the following is a component of a typical three phase cage motor?
all of the above
Which of the following is a difference b/w a vector drive and an inverter drive
all of the above
Which of the following things should be considered when ramping a motor to a speed above its base speed?
all of the above
Which of the following statements is not true of an electrical schematic?
an electrical schematic never shows electrical parameters such as voltage, current, or resistance
Examine the circuit shown and determine which type(s) of interlocking is/are shown
auxiliary contact and mechanical interlocking
Which section of an inverter drive changes the incoming AC into DC?
converter
which of the following is not a component of a transformer?
electrical coupling
which of the following allows you to control when the current will flow in a circuit?
input device
The type of manual starter used for three phase motor is a
integral horsepower starter
Which of the following is not a type of overload?
manual overload
A transformer uses the principle_____________
mutual inductance
Which of the following is not a function of motor control
none of the above
Which of the following is not a part of a fusible disconnect?
none of the above
A ground fault occurs when
one of the phases becomes grounded
Accelerating and decelerating a motor at a fixed rate is called
ramping
A________is often use to allow an operator or technician to change a machine from automatic mode to manual mode
selector switch
Based on the circuit diagram shown, what will happen to the motor if the JOG pushbutton is pressed?
the motor will run until the JOG button is released
Some manual motor starters use a special sensing coil that verifies the presence of incoming voltage to the starter when the voltage is below a present level
true
The contacts of a manual starter will remain in the actuated position when power is lost
true
The output voltage of a transformer can be determined if you know the input voltage and the turns ratio
true
The relationship b/w the input voltage and output of a transformer is based on the
turns rotation
_________protection on a manual starter will prevent the automatic restart of a motor when recovering from a power from a power loss
under voltage
