Basic Electrical Theory: Unit 20 - Motors

What is the approximate output of a 15hp motor

11 kW

What is the nameplate FLA for a 5 hp, 230V, single-phase motor, with 93% power factor and 80 percent efficiency

20A

for dual voltage 230/460V motor, the field windings are connected in parallel for --- operation and in series for --- operation

230V, 460V

What is the approximate output of a 5 hp, 480V, three phase motor

3.75 kW

What size motor, i horsepower, is required to produce approximately 30 kW of output

40 hp

What is the nameplate FLA for a 20 hp, 208V, Three phase motor with 90 percent power factor and 80 percent efficiency

58A

When a motor starts, the current drawn is at least --- times the motor FLA; this is known as motor "locked-roll-amperes (LRA)

6

Motors are used to convert electrical energy into mechanical work and the output mechanical work of a motor is rated in horsepower. 1 hp= ----

746W

Motors must be protected against excessive windings heat by a properly sized overload protection device based on the motor --- current rating

FLA

If the rotating part of the motor winding is jammed so that it cannot rotate, no CEMF is produced in the motor winding. As a result, the motor operates at __________ and the winding will be destroyed by excessive heat.

LRC

DC motors use brushes with springs to hold them in contact with a ----

commutators

If the speed of a dc motor begins to increase, the armature will cut through the electro magnetic field at an increasing rate. This results in a greater armature CEMF, which acts to cut down on the increased armature current, resulting in the motor speeding up.

false

Placing a load on a shunt-wound dc motor causes the motor to slow down, which increases the rate at which the field flux lines are cut by the armature. As a result, the armature CEMF increases producing an increase in the applied armature voltage and current. The increases in current results in increased motor speed.

false

The motor FLA rating is used when sizing motor conductors or circuit protection

false

dual voltage ac motors are made with two field windings. The field winding are connected in ---- for low-voltage operation and in --- for high voltage operation

parallel, series

To reverse the rotation of a dc motor, you must reverse the ______________.

stator field or rotor field

In a ---- motor, the rotor is actually locked in step with the rotating stator field and is dragged along at the speed of the rotating magnetic field

synchronous

In an ac induction motor, the stator produces a rotating magnetic field that induces current in the rotor windings. The rotor current generates a magnetic field of the stator, thereby causing the rotor to run

true

Once a motor begins turning, the rotor windings a increasingly cut by the stationary magnetic field, resulting in an increasing counter-electromotive force.

true

The actual motor current depends upon the load on the motor and the operating voltage at the motor terminals

true

a motor must have two opposing magnetic fields in order to rotate. The stationary field winding is mounted on the starter, and the rotating part is referred to as the armature

true

Swapping ---- of the line conductors can reverse a three-phase ac motors rotation

two

----- motors are fractional horsepower motors that operate equally well on ac and dc and are used for vacuum cleaners, electric drills, mixers, and light house appliances

universal

the nameplate motor FLA rating describes the motor current rating when it carries its rated horsepower load at its rated ----

voltage