Page 350 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Since the current carrying rotor conductors are placed in the magnetic field produced by the stator winding. As
a result, the rotor conductors experience mechanical force. The sum of the mechanical forces on all the rotor
conductors produce a torque which moves the rotor in the same direction as the rotating magnetic field. Hence, in
such a way the three phase input electric power is converted into output mechanical power in a 3-phase induction
motor.
Also, according to Lenz’s law, the rotor should move in the direction of the stator field, i.e., the direction of rotor
currents would be such that they tend to oppose the cause producing them. Here, the cause producing the rotor
currents is the relative speed between the RMF and the rotor conductors. Thus to reduce this relative speed, the
rotor starts running in the same direction as that of the RMF.
Advantages of Three Phase Induction Motor
Following are the chief advantages of a 3-phase induction motor :
It has simple and rugged construction.
It requires less maintenance.

It has high efficiency and good power factor.
It is less expensive.
It has self-starting torque.
Disadvantages of Three Phase Induction Motor

The disadvantages of a 3-phase induction motor are given as follows:
The 3-phase induction motors are constant speed motors; hence their speed control is very difficult.
3-phase induction motors have poor starting torque and high inrush currents (about 4 to 8 times of the rated
current).
They always operate under lagging power factor and during light loads, they operate at very worst power factor
(about 0.3 to 0.5 lagging).
PID Controller

A PID (Proportional – Integral – Derivative) controller is an instrument used by control engineers to regulate
temperature, flow, pressure, speed, and other process variables in industrial control systems. PID controllers use
a control loop feedback mechanism to control process variables and are the most accurate and stable controller.
PID Controller Basics
The purpose of a PID controller is to force feedback to match a setpoint, such as a thermostat, that forces the
heating and cooling unit to turn on or off based on a set temperature. PID controllers are best used in systems
which have a relatively small mass and those which react quickly to changes in the energy added to the process.
AC Drive Installation
Overview This publication identifies important installation considerations for Allen-Bradley adjustable frequency
AC drives. Precautions Qualified Personnel General Reference Materials . Installation Considerations Configure
For Non-Solid Grounded Distribution Systems Your drive may contain protective MOVs and common mode
capacitors that are referenced to ground. Disconnect these devices from ground when installing the drive on any
of the following non-solid grounded distribution systems: Measure Input Impedance Do not install a drive on a

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CITS : E & H - Electronics Mechanic - Lesson 223 - 236