Friday, May 23, 2008

"Geared-down" to troubleshoot !

It was one of my earliest commissioning assignments. The job was ideal for a rookie. Just a 45 kW dc drive with very simple functionality. Start, stop and speed set potentiometer. The control panel was built with care and installed properly. All I had to do was to conduct routine checks and start the drive return home.
Cochin Kadalas (Kadalas means paper in Malayalam-Kerala, India) was the factory in which I had to do all this.
Everything went as per expectations. The only hitch was that the place was so hot and humid that, half an hour after I started my work, I looked as if I had fallen into a pool fully clothed and got out. I was sweating so profusely. When it became impossible to bear, I took my shirt off and that is the only time I have conducted official work so dressed, I mean, undressed.
When it was sure that the drive and the paper machine to it was driving were working as expected under no-load, paper pulp was made and conveyed to the machine. As soon as the pulp entered between the rollers the machine stopped. The ammeter indicated full rated current. I opened up the panel and increased the current limit to the rated overload limit. No change. The machine refused to work.
All kinds of investigations followed. But the situation did not change.
The machinery was installed by a man who barely spoke Hindi. All he knew was Bengali. With my broken Hindi and more broken Bengali, I tried to find out more about the machinery, with the hope of finding out the reason for the stalled machine. While we were having this conversation, he commented that he had very recently commissioned an identical machine successfully. I tried to interrogate him to find out if there was even a minor difference between that and this machine. He kept insisting that there were none.
While all this was going on, he let slip that the motor in the earlier case was a 750 rpm machine and that this one was ‘unnecessarily’ 1440 rpm.
Ah ha! The gearbox between the motor and the machine was also exactly as in the previous case.
Now it was clear that the motor was delivering half the power required because it was running at half the speed!
I had a tough time convincing the non-engineers that we either had to change the motor or the gearbox. Finally the latter was done and my one-day-assignment ended after nearly a week.

------ J L Anil Kumar

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