PRACTICAL
-2
AIM:
STUDY OF ENERGY EFFICIENT MOTORS.
OBJECTIVES: after studying this experiment, it will be possible
to;
(I) Identify various
electrical, mechanical, magnetic & design parameters responsible for energy
efficient motors.
(II) Categorization
of various losses occurring during the operation of motors.
(III)
Identify various
measures to improve the efficiency.
(IV) Advantage of
energy efficient motors.
SIGNIFICANCE: Statistical data shows that the electrical motors
consume more than half (50%) of the total electricity produced and (2) more
than 75% of the electrical consumption in industry. Further it is major
equipment responsible for low power factor in the system. So if various
parameters and design factors are considered in appropriate conditions, the
motor performance improves which result into saving of electrical and
mechanical energy. This is the concept of energy efficient motors.
THEORY:
Electrical
motor is a device which converts the electrical energy into mechanical energy.
This conversion when considered in relative aspects defines the efficiency as
follows:
Efficiency η = mechanical
input/electrical input
= output/input
= output/(output + losses)
= (input – losses)/input
As there are various types of
motors
(1) Operating
on a.c./d.c. supply
(2) Working
on 1-phase/3-phase
(3) Working
on the principle of dynamically induced e.m.f., rotating magnetic field
(4) Magnetic
locking, reluctance, hysteresis & some other.
There are various types of motors
(1)
Stator/field
system
(2)
Rotor/armature
As a result of interaction of electric and magnetic
energy within this part mechanical energy produced which is utilized for
various purpose. As the mechanical energy is not directly converted from
electrical energy but takes the path through magnetic energy, the various
losses occurring between as well as in electrical and mechanical form. The
losses are recognized as under:
(1)
Rotor copper
losses
(2)
Stator copper
losses
(3)
Core losses(i)
Hysteresis losses (ii) eddy current losses
(4)
Windage and
friction losses
(5)
Stray load
losses-which is partly electrical and mechanical
Further, the motor is designed considering one of
the following parameters which also affect the motors performance considerably.
(1)
Voltage
(2)
Frequency
(3)
Voltage
unbalance
(4)
Load
(5)
Output
(6)
Speed
(7)
Sleep
When we consider the duty of the motor it classifies
it into three classes.
(1)
Continuous duty
(2)
Intermittent
duty
(3)
Short duty
Thus the performance of motor depends on all such
instant mixture of selected parameters set which defines its losses and
ultimately the efficiencu of energy conversion. This is the base for developing
energy efficient motors. When we develop the energy efficient motors, we also
consider the factors such as:
CHARACTERISTICS:
(1)
Starting
characteristics
(2)
Running
characteristics
(3)
No load
characteristics
(4)
Torque/speed
characteristics
(5)
Torque/slip
characteristics
The following design parameters are also considered.
DESIGN
PARAMETERS:
1.
Physical
parameters: Size of machine,
length & diameter of machine, weight of machine, cross sectional area of
conductors, width of slots. Resistivity, conductivity of materials, air gap
etc.
2.
Electrical
parameters: Voltage rating,
frequency, current density, di-electric strength of materials, resistance and
inductance of material, various capacitive effects, etc.
3.
Magnetic
parameters:
Flux density, mmf, magnetic saturation limit, permeability of material,
armature reaction etc.
4.
Thermal
parameters: Cooling
path, thermal insulation, air flow etc.
5.
Mechanical
parameters: Speed, torque, slip,
etc.
Thus all such conditions are necessary for
developing energy efficient motors, when considered appropriately. It thus
results into the measures of improving the efficiency of motors.
