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