ME 2205 ELECTRICAL DRIVES AND CONTROL

UNIT I INTRODUCTION BY

B.DURAI BABU 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• CONTINOUS DUTY,VARIABLE LOAD• SHORT TIME DUTY• INTERMITTENT PERIODIC DUTY• INTERMITTENT PERIODIC DUTY WITH STARTING• 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 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 QUADRANT

POLARITY OF VOLTAGE

POLARITY OF CURRENT

NATURE OF OPERATION

I POSITIVE POSITIVE FORWARD MOTORING

II POSITIVE NEGATIVE FORWARD REGENERATION

III NEGATIVE NEGATIVE REVERSE MOTORING

IV NEGATIVE POSITIVE REVERSE REGENERATION