CHAPTER 2 ELECTRIC MOTORS Flashcards
• 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.
electric motorS
• 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
60, 1800, 3600, 1725, 3450
• Electric motors are rated in __________/
horsepower
1 hp = _________ ft - lb/min
__________ ft-lb / s
33,000, 550
• at startup, consumes substantially more electrical power
inrush current
In theory, one horsepower is equivalent to ______W.
746
• An electric motor’s _____________ (LRA) is the highest amperage that a motor pulls.
locked rotor amperage
A motor operating at its rated speed, voltage, and horsepower draws current at its ______________ or ______________.
full load amperage (FLA), running load amperage (RLA)
electric motor’s LRA is usually _____ to ____ times greater than the FLA/RLA.
four to six
• Most electric motors are designed to run at ___% to ____% of rated load, with maximum efficiency typically near ___% of rated load.
50, 100, 75
It is a FRACTIONAL HORSEPOWER MOTOR designed to operate on both AC and DC power.
universal motor
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.
universal motor
It is used on appliances such as blenders and vacuum cleaners and power tools such as routers and electric drills.
universal motor
• 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.
SPLIT-PHASE MOTOR
This type of motor starts slowly with low torque, so it cannot begin to heavy loads
SPLIT-PHASE MOTOR
These motors use electromagnetic induction to cause the motor rotor to turn.
• Repulsion-start induction motors are capable of handling heavy starting loads.
INDUCTION MOTORS
• 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.
CAPACITOR MOTOR
• It is more efficient and has a better starting torque than the split-phase motor.
CAPACITOR MOTOR
• 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).
THREE- PHASE MOTORS
• 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.
DUAL-VOLTAGE MOTORS
The specifications of an electric motor are typically listed on the ________.
nameplate
• 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)
motor controllerS
• a CENTRALLY LOCATED, sheet metal, a cabinet-like enclosure that houses starters and controls that control and protect several motors.
motor control centers
The ______________ of an MCC contains operator controls and gauges.
front panel
• The _______ of the MCC contains plug-in units such as starters, controls, and specialized units.
interior
• 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.
VARIABLE-FREQUENCY DRIVE
