Lecture 1 to 4 introduction to electrical drive

Basics of Electric Drive are presented.

1. Introduction to Electrical Drive Prof. S. Y. Gadgune

2. Electric Drives • Systems employed for motion control are called as Drives . • It may employ any of prime movers such as diesel or petrol engines, gas or steam turbines, steam engines , hydraulic motors and electric motors, for supplying mechanical energy for motion control. • Drives employing electric motors are called as Electrical Drives .

3. Parts Of Electric Drives

4. Power Modulator • The power modulator regulates the output power of the source. • It controls the power from the source to the motor in such a manner that motor transmits the speed torque characteristic required by the load . • During the transient operations like starting, braking and speed reversing the excessive current drawn from the source. This excessive current drawn from the source may overload it or may cause a voltage drop. Hence the power modulator restricts the source and motor current .

5. Power Modulator • The power modulator converts the energy according to the requirement of the motor e.g . if the source is DC and an induction motor is used then power modulator convert DC into AC. • It also selects the mode of operation of the motor, i.e . motoring or braking.

6. CONTROL UNIT • The control unit controls the power modulator which operates at small voltage and power levels. The control unit also operates the power modulator as desired . • It also generates the commands for the protection of power modulator and motor. An input command signal which adjusts the operating point of the drive, from an input to the control unit.

7. SENSING UNIT • It senses the certain drive parameter like motor current and speed. • It mainly required either for protection or for closed loop operation.

8. ADVANTAGE OF ELECTRIC DRIVES • The electrical drives are available in a wide range of torque , speed and power. • They are adaptable to almost any operating conditions such as explosive and radioactive environment , submerged in liquids, vertical mounting and so on. • The electrical drive does not pollute the environment. • It can operate in all four quadrants of speed torque plane. • They can be started instantly and can immediately be fully loaded. i.e., there is no need to refuel or warm up the motor .

9. ADVANTAGE OF ELECTRIC DRIVES They have flexible control characteristic and can be employed to automatically control the drive. Because of the above advantages, the mechanical energy already available from a non-electrical prime mover is sometimes first converted into electrical energy by a generator and back to a mechanical energy of an electrical motor. Electrical link thus provides between the non-electrical prime mover and the load impact to the drive flexible control characteristic.

10. Disadvantage Of Electric Drives • The power failure completely disabled the whole of the system. • The application of the drive is limited because it cannot use in a place where the power supply is not available . • It can cause noise pollution. • The initial cost of the system is high.

11. Parts of electrical drives 1) Electrical Motors DC Motors- Shunt Series, Compound, Separately Excited Induction Motors- Squirrel Cage, Slip Ring Synchronous Motors- Cylindrical Rotor, Salient pole, PMSM Special motors- BLDC, Stepper Motors etc

12. Power Modulators Power Modulators – are the devices which alter the nature or frequency as well as changes the intensity of power to control electrical drives. Roughly, power modulators can be classified into three types, 1) Converters 2) Variable impedance circuits 3) Switching circuits. As the name suggests, converters are used to convert currents from one type to another type. Depending on the type of function, converters can be divided into 5 types – 1) AC to DC converters 2) AC regulators 3) Choppers or DC-DC converters 4) Inverters 5) Cycloconverters

13. Sources Sources may be of 1 phase and 3 phase. 50 Hz AC supply is the most common type of electricity supplied in India, both for domestic and commercial purpose. Synchronous motors which are fed 50 Hz supply have maximum speed up to 3000 rpm, and for getting higher speeds higher frequency supply is needed. Motors of low and medium powers are fed from 400 V supply, and higher ratings like 3.3 kV, 6.6 kV, 11 kV etc are provided also.

14. Control Unit Choice of control unit depends upon the type of power modulator that is used. These are of many types, like when semiconductor converters are used, then the control unit consists of firing circuits, which employ linear devices and microprocessors.

15. Choice of electrical drive Choice of an electric drive depends on a number of factors. Some of the important factors are 1 . Steady State Operating conditions requirements: Nature of speed torque characteristics, speed regulation, speed range, efficiency, duty cycle, quadrants of operation, speed fluctuations if any, ratings etc 2 . Transient operation requirements: Values of acceleration and deceleration, starting, braking and reversing performance. 3 . Requirements related to the source: Types of source and its capacity, magnitude of voltage, voltage fluctuations, power factor, harmonics and their effect on other loads, ability to accept regenerative power

16. Choice of electrical drive 4. Capital and running cost, maintenance needs life. 5 . Space and weight restriction if any. 6 . Environment and location. 7 . Reliability.

17. References G. K. Dubey , “Fundamentals of Electrical Drives”, Second Edition, Narosa Publishing House

18. Thank You