Monday, May 22, 2006

THE MOTOR WHICH REFUSED TO BEHAVE !!!

About three decades back, immediately on completion of my studies, I joined a major electrical manufacturing company in India. As a part of my training during the first year, I was deputed to a project site where electrics for a rolling mill were being commissioned. I was assigned to a team, which was installing and commissioning control room plenum ventilation system. The system consisted of huge ventilation room which was fed by two large ventilation blowers on the east and west side of the control room (one on either side).

Fresh from the college, I was raring to go to display all my newly acquired (?) knowledge! My task was to assist a team (which basically meant holding the multimeter and megger!).I started my work with great alacrity! After checking up the connections, supply to the three-phase induction motor driving the east side ventilation blower was switched on. The motor started rotating but in the reverse direction! I concluded (and I was very proud of it!) that the connections to the two phases need to be interchanged. We did it at the motor terminals and switched it on. No change in the direction of rotation! I was truly stumped. Were all my fundamentals wrong?
My senior colleague also noticed that the motor was rotating at much smaller speed.(about one-fifth of the synchronous speed).This was another assault on my “fundamentals” since i was taught that under normal conditions an inductions always runs at slightly below the synchronous speed and cannot run at such low speeds.
A great deal of time was spent to find out the problem with no success. The electrical team was under tremendous pressure from the client as the next day was the D-day for commissioning. It was almost the closing time.

All of a sudden one of our colleague came running and wanted to know why the ventilation motor on the west side was running! This was totally unexpected.
Then it dawned on us that when we were switching on (what we thought) the east side motor, actually the west side motor was getting switched on (obviously due to wrong cabling). The air pushed by the west side ventilation motor through the common duct was causing east side blower and hence the motor to rotate at a slow speed.
Of course, once the cause was known, it was easy to set right the things and go ahead with the commissioning the next day.

Sunday, May 21, 2006

About Electrical Anecdotes

As compared to the other branches of engineering such as civil, mechanical, chemical etc., the electrical engineering abounds in abstract/invisible entities like current, flux, power factor, reactive power, charge and so on. This makes their study more frustrating or more fascinating depending on how we were taught! In the initial years of my engineering study, when we were required to study basics of all engineering streams, the electrical subject was voted as most difficult by the students.

However, the point I am now putting forth is, that the testing and commissioning of the electrical systems is more challenging and complex because one cannot see and visualize the happenings as in case of say civil or mechanical engineering projects. Try explaining to a non-electrical person that some electrical actuator operated on its own due to a stray pick-up.

The unique and peculiar nature of this field has led to sometimes amusing situations in the course of my practice. I am sure, many of us would have come across puzzling and intriguing situations and successfully got over it. Therefore it struck me that it would be great to create a forum where fellow professionals can share such anecdotes/experiences. Apart from being interesting, it could prove useful too!

I welcome you to go ahead and start mailing your experiences in brief to me at nagrajrao@ieee.org, and I will post it on this web site.