14-08-2012, 03:05 PM
ELECTRICAL DRIVES
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INTRODUCTION: ELECTRICAL DRIVES
A complete production unit consists primarily of three basic components:
1. ELECTRIC MOTOR
2. ENERGY-TRANSMITTING DEVICE
3. WORKING(OR DRIVEN MACHINE)
An electric motor is the source of motive power.An energy transmitting device delivers power from electric motor to the driven machine(or the load);it usually consists of shaft,belt,chain,rope etc.A working machine is the driven machine that performs the required production process.Examples of working machines are lathes,centrifugal pumps,drilling machines,lifts,conveyor belts,food-mixers etc.
DRIVE:
Drives are employed for systems that require motion control – e.g. transportation system, fans,robots, pumps, machine tools, etc. Prime movers are required in drive systems to provide the movement or motion and energy that is used to provide the motion can come from varioussources: diesel engines, petrol engines, hydraulic motors, electric motors etc.
Drives that use electric motors as the prime movers are known as electrical drives.
ELECTRIC DRIVE:
An electric motor together with its control equipment and energy-transmitting device forms an ELECTRIC DRIVE.An electric drive together with its working machine constitutes an electric-drive system.A ceiling-fan motor with its speed regulator but without blades is an example of electric drive.
Other examples of electric drives are: a food-mixer without food to be processed,a motor and conveyor-belt withot any material on its belt.Some examples of electric-drive systems are: a ceiling-fan motor with regulator and also with blades,a food mixer with food to be processed,a motor and conveyor-belt with material on its belt and so on.
ADVANTAGES OF ELECTRIC DRIVES:
1. Flexible control characteristic – This is particularly true when power electronic converters are employed where the dynamic and steady state characteristics of the motor can be controlled by controlling the applied voltage or current.
2. Available in wide range of speed, torque and power
3. High efficiency, lower noise, low maintenance requirements and cleaner operation
4. Electric energy is easy to be transported.
5. Adaptable to various operating conditions: explosive, submerged in liquid, various types of mounting, etc
6. Can be started instantly and can be fully loaded immediately (no need to warm-up the motor).
CONVENTIONAL VARIABLE SPEED ELECTRIC DRIVE SYSTEM:
A typical conventional electric drive system for variable speed application employing multimachine system is shown in figure above.The system is obviously bulky, expensive, inflexible and require regular maintenance. In the past, induction and synchronous machines were used for constant speed applications – this was mainly because of the unavailability of variable frequency supply.
BLOCK DIAGRAM OF CONVENTIONAL ELECTRIC DRIVE SYSTEM
ELECTRIC DRIVE SYSTEM USING POWER ELECTRONIC CONVERTER:
With the advancement in power electronics, microprocessors and digital electronics, typical electric drive systems nowadays are becoming more compact, efficient, cheaper and versatile – this is shown in figure below. The voltage and current applied to the motor can be changed at will by employing power electronic converters. AC motor is no longer limited to applications where only AC source is available, however, it can also be used when the power source available is DC or vice versa.
BLOCK DIAGRAM OF ELECTRIC DRIVE SYSTEM USING POWER ELECTRONIC CONVERTER
TYPES OF ELECTRIC DRIVES:
There are two types of electric drives depending upon the motive power in the two drives provided by d.c. motors and a.c. motors respectively,namely:
1. D.C. DRIVES
2. A.C. DRIVES
D.C. DRIVES: D.C. motors are used extensively in adjustable –speed drives and position control applications. Their speed below base speed can be controlled by armature-voltage control. Speed above base speed are obtained by field flux control. As speed control methods for d.c. motors are simpler and less expensive then those for a.c. motors,d.c. motors are preferred where wide-speed control range is required.
A.C. DRIVES:
The term “A.C. drives” is used to refer to equipments designed to control the speed of an AC motor. AC drives receive AC power and convert it to an adjustable frequency, adjustable voltage output for controlling motor operation. Modern a.c. drives make use of power converters.
ADVANTAGES OF A.C. DRIVES OVER D.C. DRIVES:
1. For the same rating,a.c. motors are lighter in weight as compared to dc motors.
2. AC motors require low maintenance as compared to dc motors.
3. AC motors are less expensive as compared to equivalent dc motors.
4. AC motors can work in hazardous areas like chemical, petrochemical etc whereas dc motors are unsuitable for such environments because of commutator sparking.
[attachment=31510]
INTRODUCTION: ELECTRICAL DRIVES
A complete production unit consists primarily of three basic components:
1. ELECTRIC MOTOR
2. ENERGY-TRANSMITTING DEVICE
3. WORKING(OR DRIVEN MACHINE)
An electric motor is the source of motive power.An energy transmitting device delivers power from electric motor to the driven machine(or the load);it usually consists of shaft,belt,chain,rope etc.A working machine is the driven machine that performs the required production process.Examples of working machines are lathes,centrifugal pumps,drilling machines,lifts,conveyor belts,food-mixers etc.
DRIVE:
Drives are employed for systems that require motion control – e.g. transportation system, fans,robots, pumps, machine tools, etc. Prime movers are required in drive systems to provide the movement or motion and energy that is used to provide the motion can come from varioussources: diesel engines, petrol engines, hydraulic motors, electric motors etc.
Drives that use electric motors as the prime movers are known as electrical drives.
ELECTRIC DRIVE:
An electric motor together with its control equipment and energy-transmitting device forms an ELECTRIC DRIVE.An electric drive together with its working machine constitutes an electric-drive system.A ceiling-fan motor with its speed regulator but without blades is an example of electric drive.
Other examples of electric drives are: a food-mixer without food to be processed,a motor and conveyor-belt withot any material on its belt.Some examples of electric-drive systems are: a ceiling-fan motor with regulator and also with blades,a food mixer with food to be processed,a motor and conveyor-belt with material on its belt and so on.
ADVANTAGES OF ELECTRIC DRIVES:
1. Flexible control characteristic – This is particularly true when power electronic converters are employed where the dynamic and steady state characteristics of the motor can be controlled by controlling the applied voltage or current.
2. Available in wide range of speed, torque and power
3. High efficiency, lower noise, low maintenance requirements and cleaner operation
4. Electric energy is easy to be transported.
5. Adaptable to various operating conditions: explosive, submerged in liquid, various types of mounting, etc
6. Can be started instantly and can be fully loaded immediately (no need to warm-up the motor).
CONVENTIONAL VARIABLE SPEED ELECTRIC DRIVE SYSTEM:
A typical conventional electric drive system for variable speed application employing multimachine system is shown in figure above.The system is obviously bulky, expensive, inflexible and require regular maintenance. In the past, induction and synchronous machines were used for constant speed applications – this was mainly because of the unavailability of variable frequency supply.
BLOCK DIAGRAM OF CONVENTIONAL ELECTRIC DRIVE SYSTEM
ELECTRIC DRIVE SYSTEM USING POWER ELECTRONIC CONVERTER:
With the advancement in power electronics, microprocessors and digital electronics, typical electric drive systems nowadays are becoming more compact, efficient, cheaper and versatile – this is shown in figure below. The voltage and current applied to the motor can be changed at will by employing power electronic converters. AC motor is no longer limited to applications where only AC source is available, however, it can also be used when the power source available is DC or vice versa.
BLOCK DIAGRAM OF ELECTRIC DRIVE SYSTEM USING POWER ELECTRONIC CONVERTER
TYPES OF ELECTRIC DRIVES:
There are two types of electric drives depending upon the motive power in the two drives provided by d.c. motors and a.c. motors respectively,namely:
1. D.C. DRIVES
2. A.C. DRIVES
D.C. DRIVES: D.C. motors are used extensively in adjustable –speed drives and position control applications. Their speed below base speed can be controlled by armature-voltage control. Speed above base speed are obtained by field flux control. As speed control methods for d.c. motors are simpler and less expensive then those for a.c. motors,d.c. motors are preferred where wide-speed control range is required.
A.C. DRIVES:
The term “A.C. drives” is used to refer to equipments designed to control the speed of an AC motor. AC drives receive AC power and convert it to an adjustable frequency, adjustable voltage output for controlling motor operation. Modern a.c. drives make use of power converters.
ADVANTAGES OF A.C. DRIVES OVER D.C. DRIVES:
1. For the same rating,a.c. motors are lighter in weight as compared to dc motors.
2. AC motors require low maintenance as compared to dc motors.
3. AC motors are less expensive as compared to equivalent dc motors.
4. AC motors can work in hazardous areas like chemical, petrochemical etc whereas dc motors are unsuitable for such environments because of commutator sparking.