Module 3: Electric Motors Flashcards
device used to convert electrical energy into mechanical energy
electric motor
considered to be a more efficient means of converting energy into mechanical energy compared to gasoline and diesel engines
electric motor
energy conversion efficiency of electric motor is 50 to 99%
true or false
true
energy conversion efficiency of a diesel engine is ___-36%
30
energy conversion efficiency of a gasoline engine is 50-99%
true or false
false; 25 to 30 %
50-99% is for electric motor
main application of electric motor
used as prime movers for stationary and indoor equipment such as those for processing of farm products and by-products
advantages and key features of electric motors
- low initial cost
- compact
- long life
- simple to operate
- quiet operation
- no exhaust fumes
- potential for automatic control
+++
- available in different hp sizes
- relatively inexpensive to operate
different hp sizes of electric motors
fractional hp sizes
- 1/4
- 1/2
- 3/4
integral hp sizes
- 1
- 1 1/2
and so forth…
common hp sizes of electric motors used
fractional hp sizes
- 1/4, 1/2, 3/4 hp sizes
costs of operating electric motor, diesel and gasoline engines
elec motor - Php 8.75/kW-hr
diesel engine - Php 9.17/kW-hr
gasoline engine - Php 23.85/kW-hr
disadvantages of using electric motor
- not adapted to mobile applications unlike engines
- used only in farms with elec lines
- affected by power outtages
classification of electric motor based on elec service
- single-phase alternating current (<5 hp)
- three-phase alternating current (>5 hp)
- direct current (use of storage battery)
most common ay #1
basic electrical principles
- electromagnets
- electromagnetic induction
- alternating current
2 major parts of an electric motor
- stator - stationary part
- rotor - rotating part
select a motor whose torque output is equal to the torque required by the load
true or false
false; torque output should always be greater than the requirement
determines the size and capacities of the electrical installations needed to operate the motor (transformer capacity, wire size, breaker capacity, switch, etc.)
starting current requirement
this is determined by the kVa rating of the motor indicated by a motor code letter
starting current requirement
the temperature rise shall not exceed the limit for the insulation class when the motor is loaded to its rating or its service factor load
true or false
true
motors are built with how many insulation classes that can withstand only certain levels of operating temperature
four insulation classes
refers to how frequently the motor is started and how long it will run each time it is started
duty rating
2 types of duty rating
- continuous duty rating
- intermittent duty rating
duty rating
motor is operated for more than an hour without rest
continuous duty rating
duty rating
operated for only few minutes at a time with rest between operations
intermittent duty rating
case or housing which prevents the operator from accidental contact with energized parts and protect the motor from physical damage
enclosure
2 types of enclosure
- open type
- totally-enclosed
enclosure
allows easy movement of air through the inside of the motor by providing slots or holes in the end shields or frame where the air can pass through
open type enclosure
enclosure
does not allow entry entry of air inside the motor
fan blows air on the outside surface of the frame to dissipate heat
totally-enclosed enclosure
fins are constructed on a motor’s enclosure to??
increase the surface are for heat dissipation
indicates the maximum load that can be successfully carried by the motor if it is to operate continuously and remain within a safe temperature range
service factor
the service factor is multiplied by the horsepower rating to give the _________ ______ the motor can sustain
maximum load
carries a good deal of essential information about the motor and should be referred to when specifying, buying, installing, replacing, operating and repairing motors
motor nameplate
for most residential and agri structures, this type of motor is widely used
alternating current motor
this is produced from winding insulated wire around a soft iron core
electromagnet
as the current passes through the coil, what is produced?
magnetic field (that has 2 diff poles: north and south which is based on the direction of current flow)
when a conductor passes through a magnetic field, what is induced?
a current (electromagnetic induction)
in electromagnetic induction, the induced voltage is controlled by different factors which are?
- strength of the magnetic field
- the rate at which the conductor is cutting the flux lines of the magnetic field
- number of conductors in which it changes its direction in an interval
a current in which it changes its direction in an interval
alternating current
main part of the motor that is made of paired slotted cores of soft iron sections
stator
main part of motor that is referred to as the armature of the motor
rotor
in a motor, the cores are wind with insulated copper that forms different pairs of magnetic poles
then the stator windings are connected to an ___ sources to form ________
AC source; electromagnets
normal ambient temp for motor operating is ______
40 ‘C
formula for computing starting current requirement (amp)
A = output power x motor horsepower / voltage rating
