Ee1451(Unit v)
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Transcript of Ee1451(Unit v)
UNIT V
DRIVES AND THEIR INDUSTRIAL APPLICATIONS
ELECTRIC DRIVES
An electric drive is a system that converts electrical energy to mechanical energy • Electric motors provide the most common
motive power for driving the wheels of industry.
They are adaptable to any type of load requirements
Types of drives
Individual drive – an single electric motor is used to drive one individual machine.
Group drive – in which a single electric motor drives a line shaft by means of which an entire group of machines may be operated
Factors affecting choice o motors
Electrical characteristics Mechanical characteristics
a) Type of enclosures
b) transmission of drive
Load types
Active load –which are due to the forces of gravity, tension and independent of loads. eg. paper mill drive
Passive load – which are due to friction, cutting and deformation of in elastic drives
eg. Aero planes, high speed hoists.
Load characteristics
Steady state characteristics
Transient characteristics
Steady state characteristics of DC shunt motor
Speed –current curve Torque – current curve
Steady state characteristics of DC series motor
Speed –current curve Torque – current curve
Steady state characteristics of AC motor
3 phase induction motor Torque – speed curve
Torque – speed curve
Load equalization
When motor is subjected to heavy load, it will draw large current
Heavy losses and voltage drop To smoothen out the load fluctuations
is called load equalization Achieved by means of fly wheel
Variations of speed, load and motor torque
Industrial applications
Textile mill : cage type induction motors Steel polling mills: wound rotor induction
motor Paper mills: cage induction motor with
large flywheels, DC motors, Schrage motors and synchronous motor.
Mines : Ac series motor, double cage induction motor, Dc series motor.
Rating of the motor
Continuous rating Continuous maximum rating Short time rating
Heating and cooling time curve
Heating and Cooling time constant
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