Chapter 6 Unit 20
What is the approximate output of a 15hp motor
11190
What is the nameplate FLA for a 5 hp, 230V, single-phase motor, with 93% power factor and 80 percent efficiency
21.8
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
3.7 kW
What size motor, i horsepower, is required to produce approximately 30 kW of output
40
What is the nameplate FLA for a 20 hp, 208V, Three phase motor with 90 percent power factor and 80 percent efficiency
57.5
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
Swapping ---- of the line conductors can reverse a three-phase ac motors rotation
any two of the three power line conductors
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
If the rotating part of the rotating motor is jammed and that it cannot rotate, no CEMF is produced in the motor winding. As a result, the motor operates at --- and the windings will be destroyed by excessive heat
locked rotor current
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 revers the
rotator or armature magnetic filed
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
----- 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