Monday, 29 July 2013

2.practical for Energy Conservation Technique for Diploma electrical engineering.


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.




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