Enhancing the I/O capability of VFDs to Remove the dependency on external PLC

“Enhancing the I/O capability of VFDs to

Remove the dependency on external PLC”

Introduction

Variable frequency drives are backbone of an industrial process. Their effective control and protection adds reliability to an industrial process. The present work is focused on enhancing the fault detection mechanism of Variable Frequency Drives. Installed Variable Frequency Drives are having limitation of inputs and outputs capability; so with the help of “LOGO PLC” installed in the drive it becomes useful for extending the input and output capability of the drive as well as it is cost effective compare to the VFDs having extended input/output capability. Installed drive is having two PLC’s, one is SIEMENS basic LOGO PLC the other is expansion LOGO PLC module which are resulting in frequent failure faults of LOGO PLC modules that hampers coal transfer for plant generation.

The limitation of the LOGO PLC is that it is unable to detect faults, no monitoring, no control and it is not user friendly as well as the fault rectification time is also more. For removing the dependency of LOGO PLC on variable frequency drives, firstly this LOGO PLC is removed by initializing the new control unit in the drive which is used to handle the entire task which was earlier performed by the LOGO PLC. Secondly it was removed by transferring all the logic of LOGO PLC in the main Allen Bradley panel which is used to instruct the drive, so that we can overcome these limitations. This helps to reduce the maintenance cost and improve the process control. This Enhancement of the input/output capability of variable frequency drives to re- move the dependency on external programmable logic controller and helps in the reduction of downtime, equipment efficiency, improved critical equipment availability and system reliability. The effective fault detection proposed by the ladder logics of LOGO PLC and Allen Bradley PLC are verified by the experimental results.

Description of Variable Frequency Drive

Variable Frequency Drives also known as AC drives helps to drive a motor by varying the frequency and voltage that is supplied to the motor. Variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive and micro drive are different names for variable frequency drives. Frequency is directly comparable with the speed. In other words, the more the frequency, faster the speed goes. As per the application the speed of motor requirements may vary, the VFD can simply increase or decrease the motor speed to meet the speed requirement. 

The speed and torque of motor is controlled by varying input voltage and frequency of the drive. It offers advantages like Energy saving, removal of expensive mechanical drive components, Increase the life of motor, Decrease the line disturbances and Reduced risk of motor damage during start up and stop.

Summary  

The first phase of the title includes the reasons for the faults of LOGO PLC, its detection and troubleshooting of its input and output. The second phase includes about removal techniques of LOGO PLC. The purpose of removing the dependency of LOGO PLC on variable frequency drives is to overcome its limitations which help to reduce the cost and improve the process control. The external LOGO PLC is removed by two different methods. Firstly by initializing the new Control Unit and new Terminal Module which together performed the and operations of LOGO PLC in it, though it is advantageous at the same time it is having disadvantages like it occupies more space compared to the previous control unit used, more costly and trouble shooting problems because of the more input/output capabilities. Secondly by transferring all of it’s input/output to the main Allen Bradley panel by developing the logic in its supportive software and give digital outputs to old control unit as LOGO PLC used to give. After the removal of LOGO PLC, the fault rectification time of the drive decreases, it further improves the equipment efficiency, process control and system reliability so that it may not hamper the coal transfer for plant generation.

By: - Prof. Sonali Changla

Rai University, Ahmedabad.