1. TIRUCHENGODE 637 215 DISTRIBUTION AND UTILIZATION V A KUPPUSAMY, M.E., MISTE., Sr. Lecturer / EEE K.S.R. POLYTECHNIC COLLEGE TIRUCHENGODE – 637 215 Prepared by Unit - II Industrial Drives127/12/2017

2. Industrial Drives Unit – II

3. Introduction Obtaining electric drives, both A.C and D.C motors are used. However A.C system is preferred. The utilisation of electric energy is always advantageous as it is cheaper. It can be easily transmitted at comparatively low line losses. It is easy to maintain the voltage at consumer premises within the prescribed limits and it is possible to increase or decrease the voltage without appreciable loss of power. In spite of the advantages of AC system some times it becomes essential to use D.C energy as industrial drive. Industrial Drives327/12/2017

4. Electric Drives An electric drive is defined as a form of machine equipment designed to convert electrical energy into mechanical energy and provide electrical control of this process. Industrial Drives427/12/2017

5. Advantages of Electric Drives It is simple in construction and has less maintenance cost. Its speed control is easy and smooth. It is neat, clean and free from any smoke or flue gases. It requires less space. It can be installed at any desired convenient place. It has comparatively longer life. It can be started immediately without any loss of time. Transmission of power from one place to other can be done with the help of cables in stead of long shaft etc. It can be remotely controlled. Industrial Drives527/12/2017

6. Parts of Electric Drives Electric drive has three important parts namely. 1. Load2. Motors3. Control Unit Load The load which connects with the shaft of electric motor is called mechanical load. The load is connected with the motor shaft either through direct, or belt, or chain, or gear. Motor The motor may be selected as per the load requirements. Motors commonly used in electric drives are D.C motors, Synchronous Motor or Brushless D.C motors etc Control Unit In modern electric drives, automatic operations are performed, i.e starting, Stopping, Speed control of motors, braking's, reversing are automatic for these electronic circuits used. When the control is complex, now a days programmable logic controllers (PLC) are used. Industrial Drives627/12/2017

7. Transmission of Power Various methods employed for Transmission of mechanical power are described below. 1. Direct Drive Motor is coupled directly to the driven machine with the help of solid or flexible coupling. Flexible coupling protects the motor for jerks. Its more efficient and required minimum space and it is the simplest method. It can be used where driven and driving machine speed are same. Industrial Drives727/12/2017

8. 2. Belt Drive A belt is used to transmit power from motor to driven machine through pulley system. This method gives satisfactory service. The mechanical power wasted due to slip is about 3 to 4 percentage. Maximum power of 300 H.P can be transmitted through this drive. Advantages Greater flexibility. Convenient speed ratio. Industrial Drives827/12/2017

9. 3. Rope Drive No of ropes are run in V-grooves over pulleys Used in sudden load Used in lift and cranes Negligible slip Industrial Drives927/12/2017

10. 4. Chain Drive It is very costly in comparison to belt and rope drive. It can be used for high speed ration (upto 6:1). It is more efficient and transmits large amount of power. It is noiseless, slip less and smooth in operation. 5. Gear Drive It is used when a high speed motor is to drive a low speed machine. The coupling between the two is through a suitable ratio gear box. Industrial Drives1027/12/2017

11. Types of Electric Drives The electric drives are classified into three types. They are 1. Individual drive2. Group drive3. Multi motor drive 1. Individual Drive In individual drive single electric motor is used to drive one individual machine. Most of the industries use this type of drive. Industrial Drives1127/12/2017

12. 2. Group Drive A single motor drives a number of machines. The motor is mechanically connected to a long shaft. It is also called line shaft drive. The line shaft is fitted with multistepped pulleys and belts. The driven machines are connected to these pulleys and belts for their required speed. Industrial Drives1227/12/2017

13. 3. Multi motor Drive In multi motor drives separate motors are used for operating different parts of the same mechanism. E.g., in case of an overhead crane, different motors are used for hoisting, long travel motion and cross travel motion. Such drive is also essential in complicated metal – cutting machine tools, paper making machines, rolling mills. Industrial Drives1327/12/2017

14. Factors Governing the selection of motor The following factors are taken into consideration while selecting a motor for industrial applications. 1. Electrical Characteristics Running Characteristics. Starting Characteristics. Speed Control. Baking. Industrial Drives1427/12/2017

15. b) Starting Characteristics The starting torque developed by a motor should be sufficient to start and accelerate the motor at its load to the rated speed in a reasonable time. Some motor may have to start against full load torque. E.g. motor driving grinding mills, or oil expellers, traction work etc. At the time of starting a motor, two torques come into play. The torque required to overcome the static friction and The torque necessary to accelerate the motor and its load to the desired speed. a) Running Characteristics The running characteristics of a motor include the speed – torque or the speed – current characteristics, losses, magnetising current, efficiency and power factor at various loads. The magnetising current and power factor are to be considered in case of A.C motors only.. Industrial Drives1527/12/2017

16. c) Speed Control In D.C motor the speed can be controlled by following methods. Armature control method Field control method In A.C motor the speed can be controlled by following methods. By changing the supply voltage. By changing the supply frequency. By changing the number of poles of motor By injecting emf in the rotor circuit By cascading of motors By injecting resistance in the rotor circuit. Industrial Drives1627/12/2017

17. d) Braking Load removed from electric motor and supply disconnected it will continue to run for some time due to inertia. To avoid to danger the worker quick stopping in motor is required. Its done by braking. The braking system should be reliable and quick in action. The braking torque must be controllable. There are two types of braking. Mechanical braking. Electrical braking. Industrial Drives1727/12/2017

18. 2. Mechanical Characteristics While selecting a motor for a particular drive, the mechanical characteristics are also taken into account. The following mechanical features determine the suitability of the motor. Type of enclosures Bearings Noise Transmission of drive (method of coupling) a) Types of Enclosures 1.Open type 2.Screen protected type 3.Drip proof type 4.Totally enclosed type 5. Splash proof type 6. Flame proof type 7. Pipe ventilated type Industrial Drives1827/12/2017

19. b. Bearings The parts of machines which house and support the main shaft. Bearing provide free rotation of the moving parts with minimum friction. There are two types of bearing usually employed in motors. Ball or roller bearing. Sleeve or bush bearing. Ball bearingRoller bearingSleeve bearingBush bearing Industrial Drives1927/12/2017

20. c. Noise This is another important feature to be considered while making the selection of a motor. Noise should be kept as low as possible in the workshops, hospitals and other domestic purposes. The noise may be due to bearing, vibrations, magnetic pulsations, and faulty foundations. To reduce noise, journal bearing may be used in place of ball bearings. The motor should be mounted on a heavy concrete or cast iron block. The electrical connections should be made through flexible conduits. Industrial Drives2027/12/2017

21. d. Transmission of Drives For transmit power from driving machine to driven machine power different types of drives are used. Type are Direct drive. Belt drive. Rope drive Chain drive. Gear drive 3. Size of motor I.E., Standard rating of motors Whether the motor is required for continuous load intermittent load or variable load. 4. Cost Capital cost. Running cost, power factor, losses, maintenance and depreciation etc. Industrial Drives2127/12/2017

22. 5. Nature of load 6. Appearance The motor selected must fulfil all the necessary load requirements and at the same time it should not be very costly. 7. Power supply Whether for Single phase A.C, Three Phase A.C or D.C supply. Industrial Drives2227/12/2017

23. The load may be divided according to the speed – torque characteristics into the following basic categories. 1. Loads requiring constant torque at all speeds. 2. Loads requiring torque which may increase in direct proportion to the speed. 3. Loads requiring torque which may increase with the square of speed. 4. Loads requiring torque which may decreases with the increase in speed. Nature and classification of load torque matching of speed – torque characteristics of load and motor SPEED LOAD TORQUE 1 2 3 4 Industrial Drives2327/12/2017

24. Classes of Load Duty Cycles As per IS 4722 – 1968 various load time variations are encountered the eight standard classes of duty. Continuous Duty. Short time Duty. Intermittent periodic duty. Intermittent periodic duty in the starting. Intermittent periodic duty with starting and braking. Continuous duty with intermittent periodic loading. Continuous duty starting and braking. Continuous duty with periodic speed changes. Industrial Drives2427/12/2017

25. Selection of Motors for Different Duty Cycles It denotes the motor operation at a constant load torque to reach steady state temperature. The load time and temperature time graph. Paper Mill drives, Compressors, Conveyers, Centrifugal pumps and fans are some example of continuous duty. 1. Continuous Duty Temperature Load Time (a) N θ Max Time (a) Industrial Drives2527/12/2017

26. It denotes the operation of motor at a constant load for short period followed by rest to cool down to the original starting temperature. Short time duty timings are generally 10, 30, 60, and 90 minutes. The load time and the temperature time graph are shown. Crane drives for household appliances, sluice gate drives, value drives and machine tool drives are some examples of short – time duty. 2. Short time Duty Temperature Load Time N θ Max Time Industrial Drives2627/12/2017

27. It denotes the operation of motor at a constant load for short period followed by rest to cool down to the original starting temperature. Short time duty timings are generally 10, 30, 60, and 90 minutes. The load time and the temperature time graph are shown. Crane drives for household appliances, sluice gate drives, value drives and machine tool drives are some examples of short – time duty. 3. Intermittent periodic Duty Temperature Load Time N θ Max Time R Industrial Drives2727/12/2017

28. This is intermittent periodic duty where heat losses during starting can not be neglected. Thus it consists of a period of starting, a period of operation at a constant load and rest period. The operating and rest periods are too short to attain the steady state temperature in one duty cycle. In this duty heating of machine during braking is considered to be negligible. Some example are metal cutting, drilling tool drives, mine hoist drives for lift trucks. 4. Intermittent periodic Duty with starting Temperature Load Time N θ Max Time R D One cycle N R D Industrial Drives2827/12/2017

29. This is the periodic duty where heat losses during starting and braking can not be ignored. Thus it consists of a period of starting, a period of operation with a constant load, a braking period, and a rest period. Thermal equilibrium is not reached in only duty cycle. Braking is done electrically and is quick. Several machine tool drives, drives for electric suburban trains and mine hoist are some examples of this duty. 5. Intermittent periodic Duty with starting and braking Temperature Load Time N θ Max Time D One cycle F R N F R D Industrial Drives2927/12/2017

30. Selection of Motors for Different Duty Cycles The operation of motor has a sequence of indentical duty cycle, each consisting of a period of operation and a period of operation on no load. Thermal equilibrium is not reached in one duty cycle. This duty is distinguished from the intermittent periodic duty by a period of running at constant load is followed by a period of running at no load instead of rest. Pressing, cutting, shearing and drilling machine drives are the example. 6. Continuous duty with intermittent periodic loading Temperature Load Time N θ Max Time R Industrial Drives3027/12/2017

31. The operation of motor consists of period of starting, a period of operation at constant load a period of electric braking and there is no rest period. Blooming mill is an example 7. Continuous duty with starting and braking Temperature Load Time N θ Max Time F D One cycle N F D Industrial Drives3127/12/2017

32. Operation of the motor has a sequence of indentical duty cycle, each cycle is having a period of running at one load and speed and followed by another period of running at different speed and load. There is no rest period. 8. Continuous duty with periodic speed changes Temperature Load Time θ Max D One cycle Speed N1N1 N2N2 N3N3 F2F2 F1F1 Industrial Drives3227/12/2017

33. SELECTION OF MOTORS FOR SPECIFIC APPLICATIONS 1. Paper mill- synchronous motor, Schrage motor Different thickness of papers required to vary the speed. Relative speed of rolls should be constant-Paper may be tearing. Required to adjust speed at any group of rolls relative to other in order to draw the paper. 2. Rolling mills (or) steel mills-separately excited dc motor High starting torques about2 to 2.5 times of rated torque. Strong construction. Ward Leonard speed control is used. DC motor (or )Slip ring motor are used. 3. Textile mills – Double Cage Induction Motor Group drive is employed High starting torque with constant speed Totally enclosed type enclosures are used. Industrial Drives3327/12/2017

34. 4. Cement mills Various types of loads available in a cement factory and the motor used for them are given below. a. Hammer crusher – 3 φ Slip ring Induction motor The stones are broken into small High starting torque motor required. b. Ball mills – Synchronous Motor Raw materials grind in to powder. Industrial Drives3427/12/2017

35. c. Rotary dries – Slip ring Induction Motor The cement slurry is dried by blowers The speed is varied depending air required to blow. Pole changing speed control is employed. d. Slurring pumps and agitators – 3 φ Squirrel Cage Induction Motor This is wet process. Industrial Drives3527/12/2017

36. 5. Machine tools- Shunt Motor (or) Squirrel Cage Induction Motor Starting torque is less. Different speed is obtained by using two or three speed motor with suitable gear combination. D.C shunt motors are used for machine tool application like planner where rapid reversal, and wide speed control are required. Grinders, totally enclosed motors are used to prevent metallic dust getting into it. 6. Lift and Hoists - Compound Motor (or) Squirrel Slip Ring Induction Motor Smooth and accelerating torque 2 to 2.5 times of full load torque. 7. Belt conveyor – Double Squirrel Cage Induction Motor Transport bulk materials like coal, sand with flat belt or bucket system. Requires high starting torque. Variable frequency speed control is used. Industrial Drives3627/12/2017

37. 8. Ship – Synchronous motor Three phase induction motor and synchronous motor used in big ships. Three phase alternator gives the supply to the synchronous motor. Steam turbine used as a prime mover. Voltage and frequency of the alternator used to the speed controlled. 9. Air compressor – Three Phase Induction Motor Air compressor used in pneumatic drill. Repulsion motor is used in air compressor. Single phase induction motor used in small compressors.. 10. Punches and Shears Cumulative compound motor. Three phase slip ring induction motor with fly wheel are used. Industrial Drives3727/12/2017

38. 11. Rotary printing Required variable speed motor. Slip ring induction motor are used. 12. Pump Load torque various the square of the speed. Less starting torque. Squirrel cage induction motor is used. Totally enclosed motor is preferred. Centrifugal pump Reciprocating pump Requires two times the full load torque at starting. Double cage and slip ring induction motor is used. Dc motor is used where Dc supply is available. Industrial Drives3827/12/2017

39. 13. Draught fan Single phase split phase induction motor is used Operating speed is constant. 14. Ceiling fan High starting torque required. Reach the rated speed in short time. Prevent the stalling in heavy loads. Three phase induction motor also used. 15. Cranes – D.C Series Motor. Single phase capacitor start and run motors are used for ceiling fan. Industrial Drives3927/12/2017

40. 16. Mines The various loads in mine are winders, ventilating fans, compressors, and pumps. Three phase slip ring induction motor or DC motor ward Leonard speed control is used. Conveyors required high starting torque, double cage motor is used. Compressor used for pneumatic drills. Centrifugal pumps are used to pump out the water. Small universal is used Refrigerators, shavers, vacuum cleaner, mixi, cloth washing machine. 17. Domestic appliances – Universal Motor or single Phase Induction Motor. Industrial Drives4027/12/2017

41. Braking The load is removed from an electric motor and supplied it to be disconnected it will continue to some inertia, to avoid danger to the worker and damaged to the products quick stopping the motor is done by braking. The stored energy is dissipated as heat by a brake shoe or brake lining which rubs against the brake drum. Mechanical Braking. Types of Braking Mechanical Braking. Electrical Braking. The stored energy of rotating parts is converted in to electrical energy and dissipated in the resistance in the form of heat or returned to the supply in case of electrical braking. Electrical Braking. Industrial Drives4127/12/2017

42. Advantages of electrical braking Electrical braking is smooth. Electrical braking is fast and cheap. Heat produced not effect the machine. Capacity of the system can be increased by heavy loads and high speeds. The output energy returned to the supply, Running cost saved. Easy speed control. Brake is cheap. Tear and wear will not take place. Highest initial cost. Can not be applied all types of motors. Electric braking can stop the motor but can not hold it stationary. Disadvantages of Electrical Braking. Industrial Drives4227/12/2017

43. Types of Electric Braking Plugging Braking. Dynamic Braking or Rheostatic Braking. Regenerative Braking. Plugging Braking Plugging means phase reversal. Simple method of electric braking. During braking period reverse torque produce on the motor. Special device is required to cut off the supply as soon as the motor comes to rest. This method applied to both A.C and D.C motors. Industrial Drives4327/12/2017

44. Plugging applied to D.C Shunt motor It is also known as reverse current braking. The armature terminals or supply polarity of a separately excited DC motor or shunt DC motor when running are reversed. Therefore, the supply voltage V and the induced voltage E b i.e. back emf will act in the same direction.separately excited DC motorshunt DC motor The effective voltage across the armature will be (V + E b ) which is almost twice the supply voltage. Thus, the armature current is reversed and a high braking torque is produced. Plugging is a highly inefficient method of braking because, in addition to the power supplied by the load, power supplied by the source is wasted in resistances.. a) Normal Runningb) During Braking Industrial Drives4427/12/2017

45. In D.C series motor while plugging the field current is also reversed. This results the production of the torque in the same direction as is was working normally. Plugging applied to D.C Series motor Therefore in order to develop torque in the reverse direction, the direction of field current should remain unchanged. The direction of field current remains unchanged whereas direction of armature current gets reversed. Now a total voltage (V + E b ) is available across the armature terminals i.e nearly twice of the supply voltage. It causes heavy current to flow around the circuit. Hence the additional resistance R is connected in series to limit the current. This method is simple and efficient but power is wasted in the resistance. a) Normal Runningb) During Braking Industrial Drives4527/12/2017

46. Plugging applied to Induction motor Achieved in induction motor by reversing any two of the three phases interchanged. When reversing any two phase the rotation of magnetic field is reversed. Therefore the torque produced in the rotor also will be reversed. At the instant of plugging the relative speed between the rotor conductors and the magnetic field will be approximately twice the synchronous speed. So voltage induced voltage, which causes to flow abnormal current in the stator and rotor. Therefore additional insulation is provided for the windings in order to withstand this high voltage. High resistance may have to be inserted in the rotor or stator circuit for the purpose of protection. a) Normal Runningb) During Braking Industrial Drives4627/12/2017

47. Dynamic braking to D.C shunt motor During braking, the armature is disconnected from the supply and is connected across a braking resistance the field winding remains connected to the supply as before. Now the machine will run as generator loaded with a resistance. The field current direction is as before but the armature current is in the reverse direction. Therefore retarding torque is produced. This torque is controlled by the varying resistance in the armature circuit. a) Normal Runningb) During Braking Industrial Drives4727/12/2017

48. Dynamic braking to D.C series motor The D.C series motor after being disconnected from the supply is made to excite as a series generator. The total resistance in the motor circuit should be less than the critical resistance, otherwise the generator will not be self excited. Also in order to self build up of flux the connections of the armature with respect to the field have to be reversed. Normally the starting resistance is used for braking purpose. For compound motors, dynamic braking is performed in the same way as D.C shunt motor. a) Normal Runningb) During Braking Industrial Drives4827/12/2017

49. Dynamic braking to induction motor In 3 phase squirrel cage induction motor, the stator is disconnected from the A.C supply mains and D.C supply is given to the stator winding. A steady flux is produced. The short circuited rotor cuts this steady flux and an emf is induced in these conductors. This provides the necessary braking effect. In the case of 3 phase slip ring induction motor the braking torque is controlled by adding the resistance in the rotor circuit. a) Normal Runningb) During Braking Industrial Drives4927/12/2017

50. Dynamic braking to Synchronous motor The D.C excitation is maintained and the stator is disconnected from A.C supply. Then the stator is connected across three resistance in star or delta. Now the machine operates as an alternator and the kinetic energy is dissipated in the resistance and braking will occur. a) Normal Runningb) During Braking Industrial Drives5027/12/2017

51. Regenerative Braking Applied to D.C Shunt motor If the emf induced in the motor is greater than the supply voltage power will be fed back into the supply. The emf induced in the motor depends upon the speed and excitation of the motor. If the field is disconnected from the supply and the field current is increased by exciting it by another source. a) Normal Runningb) During Braking Industrial Drives5127/12/2017

52. Regenerative Braking Applied to D.C Shunt motor In 3 phase squirrel cage induction motor, the stator is disconnected from the A.C supply mains and D.C supply is given to the stator winding. A steady flux is produced. The short circuited rotor cuts this steady flux and an emf is induced in these conductors. a) Normal Runningb) During Braking This provides the necessary braking effect. In the case of 3 phase slip ring induction motor the braking torque is controlled by adding the resistance in the rotor circuit. Industrial Drives5227/12/2017

53. Regenerative Braking Applied to D.C Series motor Regenerative braking is not applied to ordinary in D.C series motor. In regenerative braking, at the instant of reversal of armature current, the emf induced in the motor will be small. Therefore the current flow through the field is in wrong direction. This will reverse the field and causes the motor emf to help the supply voltage. This will result in short circuit of the supply. Due to these complications, this method is not used for common industrial purposes. a) Normal Runningb) During Braking D.C series motor for regenerative braking using French method. It is provided with a main series winding and auxiliary field windings connected in parallel with the main series winding in a single D.C series motor. During braking period, the auxiliary winding are put in series with each other and switched across the supply. The motor acts as a differentially compound generator. Industrial Drives5327/12/2017

54. Regenerative Braking Applied to D.C Series motor When an induction motor runs above synchronous speed the emf induced in the rotor is greater than the supply voltage. Hence the motor works as an induction generator and feeds power back to the supply line. No extra auxiliaries are needed for this purpose. Its application is very useful to lift and hoist for a descending load at a speed slightly above synchronous speed. It is also advantageous on mountain railways. Industrial Drives5427/12/2017

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