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(1)Power modulator:
Resistance controllers
Eddy current drive
MG set
The function of the power modulator is to change the electric energy of the source as per load torque speed characteristics.
(2)Control circuit:
The function of control circuit is to control - the speed, starting characteristics and braking characteristics
(3)Motor:
The motor can be ac or dc, as per the application of use of the drive.
(4)Sensing unit:
Sensing units are used to sense the parameters like speed, current etc. For sensing speed, techogenerator(shaft encoder) is used and for sensing current , current transformer(hall effect sensors) is used.
(5)Load:
Load can be of fan, pump, train(for locomotive), compressors, blowers etc.Losses in the power modulator can be reduced by using static power devices as compared to conventional modulators like resistance controllers, MG set, eddy current drive.
Advantages of electric drives:
The electric drive is being employed in all industries due to its following advantages over the mechanical drives:
• Cost is to low as compared to ather system of drive.
• The system is more simple and clean.
• The control is very easy and smooth.
• Flexible in layout.
• Facility for remote control.
• Transmission of power from one place to other can be done with the help of cables instead of long long shafts etc.
• Its maintenance cost is quite low.
• It can be started at any time without delay in time.
Disadvantages of electric drives:
No doubt electrical drive is more advantageous but it has several disadvantages also such as:
• Electric drive system is tied only up to the electrified area.
• The condition arising under the short circuits , leakage from conductors and break down of over head conductor may lead to fatal accidents.
• Failure in supply for a few minutes may paralyse the whole system.
THEORY OF ENERGY EFFICIENT DRIVES:
Losses in the electrical drives:
Losses in the electrical drive system occurs in the following places:
• Losses in the power modulator i.e. mainly in the power converters.
• Losses in the transmission medium i.e. friction losses.
• Losses in the motor: They are of five types
Copper losses,
Core losses,
Stray losses,
Windage losses,
Friction and windage losses.
• Losses in the load.
The electric drive system can be made efficient by reducing the above mentioned losses. The ways for making the elecric drive efficient are as follows:
The drive system can be made efficient by:
• Using power converters (power devices) as a power modulator.
Using the power devices the losses are less as compared to other conventional converters.
• Improving the power factor at the input source side.
By improving the power factor the losses in the motor or in the system can be considerably reduced . There are many methods for improving the power factor so, by using the suitable method we can reduced the losses much more.
• Reducing the harmonics in the system.
Harmonics in the system also affects the efficient running of the drive. So for reducing the losses , harmonics in the system should be reduced.
• Reducing the losses in the transmission.
In the transmission of power like in the motor shaft which transmits the mechanical power to the load, the friction losses occurs in the gears and bearings .So for improving the efficiency this losses should be reduced by lubricating the gears or in the other suitable way.
• Using VFD (Variable Frequency Drive).
Now a days variable frequency drives are extensively used .In this drive losses are less, so using this drive the much more efficiency can be achieved.
• Using proper rated motors.
Due to lack of awareness many people use high rated motor than actually required. In their opinion the high rated motor is safe in running and they can over load the motor since it is high rated. So the efficiency with which the motor runs is much less. So we must use the motor of right rating suitable to particular application.
• Using energy efficient motors.
By using the efficient motors, the whole drive efficiency can be increased since the losses in the efficient motor are much more less than the conventional motor.
• Reducing the voltage fluctuation.
The variation in the voltage affects the running of the motor and tends the motor to run with lesser efficiency than it actually has. So it affects the efficient operation of the drive and reducing the efficiency of the drive.
• Regular maintenance.
By regular maintenance of the drive parameters like transmission medium such as gears, bearings and of motor and other devices which required it, the losses can be kept in control and ultimately the efficiency of the whole electric drive.
So by considering above topics the electric drive can be made efficient and ultimately save the electric power. Which affects the economical aspects of the unit and so the industry which using these drives. So by using these efficient drives we can save the energy and also the money which is in terms of the electric bill.