ME 2205 ELECTRICAL DRIVES AND CONTROL UNIT I

ME 2205 ELECTRICAL DRIVES AND CONTROL UNIT I INTRODUCTION BY P. VIVEK A. P/EEE

BASIC ELEMENTS POWER SUPPLY CONTROL EQUIPME NT ELECTRIC MOTOR MECHANICAL LOAD

ELECTRICAL DRIVE • • A UNIT CONSITING OF AN ELECTRICAL MOTOR ENERGY TRANSMITTING SHAFT CONTROL EQUIPMENT

DRIVE SYSTEM • COMBINATION OF • ELECTRICAL DRIVE AND CORRESPONDING LOAD

ADVANTAGES • FEASIBLE CONTROL CHARACTERISTICS • AVAILABLE IN WIDE RANGE OF SPEED TORQUE AND POWER • HIGHER EFFICIENCY • LOWER NOISE • CLEANER OPERATION • LOW MAINTENANCE REQUIREMENTS • ELECTRIC ENERGY IS EASY TO TRANSPORT

TYPES OF ELECTRICAL DRIVES • GROUP DRIVE • INDIVIDUAL DRIVE • MULTIMOTOR DRIVE

GROUP DRIVE • DRIVE CONSISTS OF ONLY ONE ELECTRIC MOTOR WHICH DRIVES SEVERAL MACHINES • ADVANTAGE • RATING OF AN ELECTRICAL DRIVE CAN BE SMALLER • DISADVANTAGE • IF ELECTRIC MOTOR IS SUBJECTED TO ANY FAULT ALL THE EQUIPMENTS BECOME IDLE

INDIVIDUAL DRIVE • IF A SINGLE MOTOR IS USED TO DRIVE A SINGLE MACHINE AND ALL THE MECHANISMS BELONGING TO THE SAME MACHINE. • DISADVANTAGE • DUE TO POWER LOSS , THE EFFICIENCY OF SUCH DRIVE IS ALSO POOR

MULTIMOTOR DRIVE • A SEPARATE MOTOR IS PROVIDED FOR DRIVING THE SEPARATE MECHANISM • ADVANTAGES • INCREASE THE OVERALL PRODUCTIVITY

FACTORS AFFECTING THE SELECTION OF DRIVE • • LIMIT OF SPEED RANGE EFFICIENCY BRAKING STARTING REQUIREMENTS POWER FACTOR LOAD FACTOR AVAILABILITY OF SUPPLY ECONOMICAL ASPECTS

SELECTION OF MOTOR BASED ON LOAD VARIATION • • • CONTINOUS LOAD CONTINOUS VARIABLE LOAD PULSATING LOAD IMPACT LOADS SHORT TIME INTERMITTENT LOAD SHORT TIME LOAD

CLASSES OF DUTY AND SELECTION OF RATING OF MOTOR • • ONCE CYCLE OF VARIATION OF LOAD IS DUTY CONTINOUS DUTY, VARIABLE LOAD SHORT TIME DUTY INTERMITTENT PERIODIC DUTY WITH STARTING AND BRAKING

POWER LOSSES AND HEATING OF MOTOR • COPPER LOSS • CORE LOSS • POWER LOSSES CAUSE LOCALISED HEATING AND RESPONSIBLE FOR TEMPERATURE RISE OF THE MOTOR

STEADY STATE CONDITION • FINAL TEMPERATURE RISE IS REACHED WHEN THE RATE OF PRODUCTION OF HEAT AND RATE OF HEAT DISSIPATION ARE EQUAL

CONTINOUS RATING • CONTINOUS RATING OF A MACHINE IS THAT RATING FOR WHICH THE TEMPERATURE RISE IS JUST BELOW THE PERMISSIBLE VALUE OF TEMPERATURE RISE

HEATING AND COOLING CURVES • A SMALLER TIME CONSTANT IS OBTAINED FOR GOOD VENTILATION • THE TIME CONSTANT IS INVERSELY PROPORTIONAL TO SPECIFIC HEAT DISSIPATION • COOLING TIME CONSTANT IS THE TIME REQUIRED TO COOL THE MACHINE

SELECTION OF POWER RATING FOR DRIVE MOTORS • CONTINOUS LOAD • CONTINOUS RATING SPECIFIES THE MAXIMUM LOAD THAT THE MOTOR CAN TAKE OVER A PERIOD FOR TIME • CONTINOUS VARIABLE LOAD • CLASS OF DUTY IS SELECTED ON BASED ON AVERAGE POWER OR CURRENT

SELECTION OF MOTOR FOR INDUSTRIAL APPLICATIONS • • STEEL ROLLING MILLS DC MOTOR WITH WARD LEONARD SYSTEM AC COMMUTATOR MOTORS ACCURATE TORQUE AND SPEED CONTROL

CRANES AND HOISTS • SERIES MOTORS • GOOD STARTING TORQUE • ELECTRIC BRAKING AT LOW SPEED IS POSSIBLE

TEXTILE INDUSTRY • MODERATE STARTING TORQUE • CONSTANT SPEED • HIGH TORQUE SQUIRREL CAGE INDUCTION MOTOR IS PREFFERED

COAL AND MINNING INDUSTRY • COAL CUTTING OR DRILLING REQUIRES COSTANT SPEED AND HIGH STARTING TORQUE • SQUIRREL CAGE MOTORS ARE PREFFERED • CENTRIFUGAL PUMPS ARE USED IN MINNING FOR PUMPING WATER. • HIGH TORQUE SQUIRREL CAGE ARE SELECTED

IMPORTANT QUESTIONS -TWO MARKS • DRAW THE FUNCTIONAL DIAGRAM OF AN ELECTRICAL DRIVE SYSTEM • GIVE ANY TWO FACTORS THAT INFLUENCE THE CHOICE OF ELECTRICAL DRIVES • MENTION THE USAGE OF DIFFERENT TYPES OF MOTORS WITH APPLICATION IN TEXTILE MILL • WHAT IS MEANT INTERMITTENT DUTY • LIST ANY FOUR ADVANTAGES OF ELECTRIC DRIVES

IMPORTANT QUESTIONS -TWO MARKS • WHAT IS MEANT BY ELECTRIC DRIVE • DEFINE CONTINOUS RATING OF A MOTOR • WHAT IS OVERLOAD CURRENT CAPABILITY OF MOTOR • DEFINE COOLING TIME CONSTANT OF A MACHINE • NAME ANY FOUR CLASSES OF DUTY

IMPORTANT QUESTIONS -SIXTEEN MARKS • DERIVE AN EXPRESSION FOR A THERMAL MODEL OF MOTOR FOR HEATING AND COOLING. ALSO DRAW THE HEATING AND COOLING CURVE • EXPLAIN THE DIFFERENT CLASSES OF MOTOR DUTY WITH NEAT SKETCH • EXPLAIN THE VARIOUS FACTORS INFLUENCING THE CHOICE OF ELECTRICAL DRIVE

IMPORTANT QUESTIONS -SIXTEEN MARKS • PROBLEMS DISCUSSED IN THE CLASS

COMPARISON BETWEEN AC AND DC DRIVE S. NO D. C. DRIVE A. C DRIVE 1 SPEED TORQUE CAN BE ACHIEVED EASILY IT IS NOT EASTY TO ADJUST SPEED TORQUE CURVES 2 SELF STARTING NOT SELF STARTING 3 FREQUENT MAINTENANCE IS REQUIRED LESS MAINTENANCE 4 COSTLY CHEAPER 5 RECTIFYING CIRCUIT IS NECESSARY NO NEED

FOUR QUADRANT OPERATION QUADRAN POLARITY OF T VOLTAGE POLARITY OF CURRENT NATURE OF OPERATION I POSITIVE FORWARD MOTORING II POSITIVE NEGATIVE FORWARD REGENERATION III NEGATIVE REVERSE MOTORING IV NEGATIVE POSITIVE REVERSE REGENERATION