Motor Controls 31-33, 37, 41, 42

What electrical test instrument should be used to test a component for continuity? (Continuity means to determine if there is a complete circuit through the component.)

ohmmeter

Generally, with an AC three-phase wound rotor induction motor, resistance is introduced into the rotor circuit when the motor _____. a. accelerates b. reaches top speed c. a or b above d. neither a or b above

D. neither a or b above

When starting a synchronous motor, _______.

DC excitation current should not be connected to the rotor

A motor has tripped out on overload. What is the most logical first step in troubleshooting this problem?

Use an ammeter to measure the running current of the motor and compare that value to the nameplate full load current

Three-speed consequent pole motors can be wound to produce ______, _____, and _______.

constant horsepower, variable torque, and constant torque

The speed of a synchronous motor is determined primarily by the ______.

frequency of the connected power source and the number of poles the motor contains

If the number of poles in a squirrel cage motor is doubled, the speed of the motor _______.

is cut approx. in half

With a synchronous motor, an independent magnetic field is established by a _____.

rotor energized by direct current through slip rings mounted on the shaft

A characteristic of synchronous motors that is different than squirrel cage or wound rotor induction motors is ______.

they operate at the speed of the rotating magnetic field

Four-speed consequent pole motors have ________.

two windings, both of which are reconnectable

A synchronous motor is started by _______.

accelerating the motor to as high a speed as possible from the squirrel cage winding and then applying the DC field excitation

Consequent pole motors have _______.

a single winding for two speeds

With a consequent pole motor intended to operate with three speeds, if one stator winding was wound with six poles and the second was reconnectable for two or four poles, the motor would develop synchronous speeds of ______, _______, and _______.

1200 rpm, 3600 rpm, and 1800 rpm

A brushless synchronous motor results in the elimination of _______, ______, and ______.

Brushes, Collector rings, Commutators

A polarized field frequency relay consists of ________, ______, and ______.

a direct-current coil, a pivoted armature, and an induced field-current coil

Plunger-type voltage testers are sometimes preferred over voltmeters because they _____.

are not susceptible to ghost voltages

Motor control centers used throughout industry have enough energy in an arc-fault condition to kill a person standing ____ feet away.

30

The amount of torque developed by an induction motor is determined by the ___________,______________,_________ and __________. ( I don't know why this is fill in the blank)

All of the above. The strength of the magnetic field of the stator winding. The strength of the magnetic field of the rotor The phase angle difference between the rotor and the stator magnetic fields

The primary test instruments used by electricians for troubleshooting a control circuit are _____, ____, and _____.

Ammeter, voltmeter, and ohmmeter

An out-of-step relay (OSR), provided on automatic synchronous starters to protect the starting windings, will open its normally closed contacts when _______. A. the motor returns to a synchronized state after leaving it B. the amount of current induced in the field windings drops below a value determined by the core settings of the out-of-step relay C. both a and b above D. neither a or b above

D. neither a or b above

Generally, wound rotor motors are ________. A. started under load with their slip rings open B. started under load with their slip rings shunted together C not started under load with their slip rings open D. not started under load with their slip rings shunted together

D. not started under load with their slip rings shunted together

With a synchronous motor, the rotor's _______.

DC is supplied through slip rings from an external source or small DC generator attached to the end of the rotating shaft

The most common squirrel cage motors used in industry fall into the Design _____ classification.

Design B

The rotor leads of a wound rotor induction motor are marked ______.

M1, M2, and M3

A motor is tripping on overload. The nameplate indicates a full load current value of 132 amperes. When the motor is operating, ammeter readings indicate that phase I has a value of 131 amperes, phase 2 has a value of 178 amperes, and phase 3 has a value of 130 amperes. What is the most likely problem with this motor?

Phase 2 is shorted or grounded

In an AC three-phase wound rotor induction motor, speed is varied by adjusting the controller's ________.

Resistance

What is the minimum size NEMA starter that should be used to connect a 100-hp three-phase squirrel cage motor connected to a 230-volt line?

Size 5 Starter

For which of the following would you not use an NEC table? a. conductor size b. motor overload size c. short circuit protection size d. ground fault protection size

b. motor overload size

2. Which type of short-circuit protective device is least likely to be used? A.dual-element time delay fuse b. non-time delay fuse C.Inverse time breaker D.all the above are used extensively

b. non-time delay fuse

Clamp-on type ammeters ______.

can be used without breaking the circuit

With a squirrel cage motor, doubling the poles can be accomplished by reversing current through _________.

half a phase winding

An AC three-phase wound rotor induction motor has ______starting torque and ______starting current.

high, low

If the windings of a star-delta motor are such that the series delta connection gives the high speed and the parallel wye connection gives the low speed, the ________.

horsepower rating is the same at both speeds

The field discharge resistor is connected _____.

in parallel with the rotor winding

The starting current and speed of a wound rotor induction motor are controlled by adding or subtracting resistance___________________________

in series with the rotor circuit

With regard to multispeed controllers, if the phases between the high- and low-speed windings are reversed, ______, ______, and ______.

motor rotation could reverse, broken casings could result, and motor damage could result.

Another term for an AC three-phase wound rotor induction motor is _____.

slip ring motor

The starting winding of a synchronous motor resembles a(n) _____________________ winding.

squirrel cage