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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