CHAPTER 2 ELECTRIC MOTORS

Question 1

• DRIVE EXHAUST/ventilation fans, air-handling unit blowers, refrigeration equipment, air and fluid compressors and pumps, heating system circulators, and manufacturing equipment and machinery.

• designed to operate at slower speeds are LARGER, RUN QUITER, and LAST LONGER because they encounter less friction.

Answer 1

electric motorS

Question 2

• Most AC ___Hz electric motors used in North America are designed to operate at theoretical _______ or ______ revolutions per minute (rpm).

• When delivering its rated horsepower, the actual speed of a motor will be somewhat less, about _______ and _______ rpm

Answer 2

60, 1800, 3600, 1725, 3450

Question 3

• Electric motors are rated in __________/

Answer 3

horsepower

Question 4

1 hp = _________ ft - lb/min
__________ ft-lb / s

Answer 4

33,000, 550

Question 5

• at startup, consumes substantially more electrical power

Answer 5

inrush current

Question 6

In theory, one horsepower is equivalent to ______W.

Answer 6

746

Question 7

• An electric motor’s _____________ (LRA) is the highest amperage that a motor pulls.

Answer 7

locked rotor amperage

Question 8

A motor operating at its rated speed, voltage, and horsepower draws current at its ______________ or ______________.

Answer 8

full load amperage (FLA), running load amperage (RLA)

Question 9

electric motor’s LRA is usually _____ to ____ times greater than the FLA/RLA.

Answer 9

four to six

Question 10

• Most electric motors are designed to run at ___% to ____% of rated load, with maximum efficiency typically near ___% of rated load.

Answer 10

50, 100, 75

Question 11

It is a FRACTIONAL HORSEPOWER MOTOR designed to operate on both AC and DC power.

Answer 11

universal motor

Question 12

It operates at high speeds under light load and low speeds with a heavy load. • It can free idle at up to 20 000 rpm.

Answer 12

universal motor

Question 13

It is used on appliances such as blenders and vacuum cleaners and power tools such as routers and electric drills.

Answer 13

universal motor

Question 14

• The MOTOR WINDINGS ARE CONFIGURED so that single-phase AC power is split into two phases that are 1⁄2 out of phase. Available in sizes up to 1⁄3 horsepower.

Answer 14

SPLIT-PHASE MOTOR

Question 15

This type of motor starts slowly with low torque, so it cannot begin to heavy loads

Answer 15

SPLIT-PHASE MOTOR

Question 16

These motors use electromagnetic induction to cause the motor rotor to turn.

• Repulsion-start induction motors are capable of handling heavy starting loads.

Answer 16

INDUCTION MOTORS

Question 17

• This type of motor operates on single-phase AC only.

• _____________ motors have a capacitor that stores and discharges energy to help start the motor rotor.

• ______________ motors have one or more capacitors to help start and run the motor.

Answer 17

CAPACITOR MOTOR

Question 18

• It is more efficient and has a better starting torque than the split-phase motor.

Answer 18

CAPACITOR MOTOR

Question 19

• LARGE MOTORS operate more efficiently on three-phase AC power.

• A single-phase motor rated at 71⁄2 hp draws a large amount of instantaneous current at startup (up to 200 A on a 240 V single-phase circuit).

Answer 19

THREE- PHASE MOTORS

Question 20

• Motors above 1⁄4 hp are designed to operate on one of two different line voltages such as 115 V or 230 V.

• Larger motors operate more efficiently on a higher line voltage because of lower I2R losses. So, if a higher line voltage is available, it is used.

Answer 20

DUAL-VOLTAGE MOTORS

Question 21

The specifications of an electric motor are typically listed on the ________.

Answer 21

nameplate

Question 22

• a switching device designed to start, stop and protect the motor.

• provide functions such as reversing, jogging plugging, operating at several speeds, or reduced current and motor torque levels.

• They are grouped together into motor control centers (MCC)

Answer 22

motor controllerS

Question 23

• a CENTRALLY LOCATED, sheet metal, a cabinet-like enclosure that houses starters and controls that control and protect several motors.

Answer 23

motor control centers

Question 24

The ______________ of an MCC contains operator controls and gauges.

Answer 24

front panel

Question 25

• The _______ of the MCC contains plug-in units such as starters, controls, and specialized units.

Answer 25

interior

Question 26

• a SOLID STATE ELECTRONIC POWER device used for controlling the rotational speed of an AC electric motor

• when a _______ starts a motor, it initially applies a low frequency (typically 2 Hz or less) and voltage to the motor.

Answer 26

VARIABLE-FREQUENCY DRIVE