Longevity Improvement of 3-Phase AC Induction Motor Controller

Introduction

This case study involves the design and manufacturing of a customized controller for an industrial heavy metal drilling and tapping machine. The load capacity range for which the models were developed are 0.1 to 5HP; the project also involved us overcoming and controlling inductive load.

Our solution approach to this problem was a novel one among any electronics company in Gandhinagar, India. The reason being the fact that in this case one cannot directly employ solutions that have been designed for resistive loads, as inductive kickback has to be handled.

Background

The client who brought us this project has been in business for over 25 years and is a reputed and easily recognized name in the industrial circles; and they also command a significant market proportion in their geographical area.

The challenge they brought before us was to create a semi-automatic drilling and tapping machine that can perform non-stop around the clock with unwavering accuracy and precision.

Once successfully designed, this was going to be a marvel in the realm of special purpose machines.

Problems Faced By Existing Systems

The design of the existing system used an electromechanical contactor mechanism in order to switch load and change direction. Being an electromechanical system, this arrangement had a short life span. Another problem that such devices are faced with is that of decreased performance due to constant wear and tear, leading to eventual shutdown.

Design used AC-AC switching mechanism. Coupled with wear & tear there was the issue of controller panels using 440V AC for switching, leading to the problem of electrical isolation. These were exactly the issues currently plaguing our client; consequently, it also led to an increase in their service overhead.

Our challenge as an industrial automation expert was to overcome these drawbacks and propose an elegant solution to the problem.

Proposed Solution

After a detailed study of the system which involved gaining a comprehensive view of its usage patterns, our experts proposed the following solution: We intended to replace the existing contactors with solid state drives. Added to this was changing the AC-AC switching to DC-AC switching mechanism.

Of course, we realized that we would be the first electronics manufacturing company in the area to attempt this feat; it involved huge amounts of risk, but the rewards of success would be greater still.

After careful deliberation the client accepted our proposal, and we set out to work.

Journey And Learnings

We began the process by designing a scaled down prototype of the actual system, capable of handling 10% of the total load; satisfied with the results we set out to manufacture the full-scale model.

During the execution phase several challenges came up; the first was the problem of achieving electrical isolation to protect the operator. Isolation depends not only on the electronic components but also the placement and mechanical structure. We achieved 6kV body isolation and 8kV input to output isolation.

Another problem that we had to face was that of reducing the effect of electro-magnetic interference (EMI). As load switching frequency was too high, inductive kickback was going to be non-zero. This can lead to faulty triggering of load. EMI reduction was achieved by designing mains line filters & snubber.

Summary

This project was an extremely educational journey, and we gained significant insights into controlling inductive loads. Not only did we create the required range of models, we also managed to increase device life span by more than 100%. This project has made us confident about dealing with issues of inductive load control.

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