Page 200 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

iii According to number of machines
- Individual drive

- Group drive
- Multi - motor drive
iv According to dynamics and transients
- Uncontrolled transient period

- Controlled transient period
V According to methods of speed control
- Reversible and non - reversible uncontrolled constant speed
- Variable position control
- Reversible and non - reversible smooth speed control

Advantage of electrical drives
1 They have flexible control characteristics.
2 Drives can be provided with automatic fault detection systems. Programmable logic controller (PLC) and
computers can be employed to automatically control the drive operation in a desired sequence.
3 They are available in wide range of torque, speed and power.
4 They are suitable to almost any operating conditions such as explosive and radioactive environments.

5 It can operate in all the four quadrants of speed - torque plane.
6 They can be started instantly and can immediately be fully loaded.
7 Control gear requirement for speed control, starting and braking is usually simple and easy to operate.
The requirement of refuel is not necessary.
Choice (or) selection of electrical drives: Choice of an electric drive depends on the important factors are.

1 Steady state operating conditions requirements. Nature of speed torque characteristics, speed regulation,
speed range, efficiency, duty cycle, quadrants of operation, speed fluctuations if any, rating etc.
2 Transient operation requirements

3 Values of acceleration and deceleration, starting, braking and reversing performance.
4 Requirements related to the source. Types of source and its capacity, magnitude of voltage, voltage fluctuations,
power factor, harmonics and their effect on other loads, ability to accept regenerative power.

5 Space and weight restriction if any.
6 Environment and location.
7 Reliability
Group electric drive

This drive consists of a single motor, which drives one or more line shafts supported on bearings. The line shaft
may be fitted with either pulleys and belts or gears, by means of which a group of machines or mechanisms may
be operated. It is also some times called as shaft drives.
Advantages: The advantages of electrical drives include the following:
• These drives are obtainable with an extensive range of speed, power & torque.
• Not like other main movers, the requirement of refuel otherwise heat up the motor is not necessary.

• They do not contaminate the atmosphere.
• Previously the motors like synchronous as well as induction were used within stable speed drives. Changeable
speed drives utilize a DC motor.

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CITS : Power - Electrician & Wireman - Lesson 93-100