High Voltage Motors

One of the jobs I had the privilege of working on was a chip mill at St. Maries, Idaho.  The wood chips were made of scrap logs out of the woods.  The logs would be ground into chips.  Then the chips were sent through a shaker that would shake out all the rotten, worthless wood.

The remaining wood chips were sent to Rathdrum, Idaho where they were made into 4×8 sheets of chip board.  It was a good deal as it cleaned out the poor wood that is left in the forest, thus decreasing the fuel for forest fires.

My previous job had been in a large hospital where I had been connecting 100 Horse Power motors.  These motors were about 3 feet high and five feet long.  At St Maries they said we would be hooking up a 1500 Horse Power motor.  I expected the motor would be large; maybe as large as an automobile.

At that size and power, they were likely to tear themselves apart starting up, or start so slow they would burn up before getting up to speed.  A motor draws about seven times as much power to get up to speed as it uses to continue running.

I noticed we were hooking up heat banks.  The heat banks would go through heating elements that cut the voltage down.  This allowed the motor to start slow and then when it got to a certain speed an element would cut out thus increasing the voltage as the speed increased.  This all made sense.

Then they brought in the motor on a flatbed trailer.  I went out to look at it.  Here it was only about a 2 foot cube.  I wondered how they could get that much power out of such a small motor.  Then I found out that instead of operating at 240 or 480 volts, this motor operated at 13,000 volts.

That’s how they got so much power out of a small motor, and why there was the need for the heat banks.

When the chipper was first turned on, it made my hair stand on end.  If a man fell into those chippers, he wouldn’t last long enough to scream.  That machine would grind up a log 2 feet across and 20 feet long in less than five minutes.

Our company also had work at the chipboard plant in Rathdrum.  The plant was highly automated.  On the manufacturing floor there was one man who ran a bull dozer and loaded the chips into a huge hopper.

Two men sat at two controllers.  About three other men loaded the finished chip board into stacks as they came off of the machine.  There was also one man running a fork lift to haul the stacks away to store them.

The building was so large I never did see the storage area, or for that matter, a lot of other areas in it.  In fact the building was large enough that when we did work in the middle of the winter, a separate building – within the main building – was built, insulated, and heated so that we could have a warm place to eat our lunch.

While I was there doing electrical work, an engineer from our office came to visit the jobsite and see how we were doing.  He asked me how I had enjoyed the job at the chip mill in St. Maries.  I told him I was amazed by such a powerful motor and how the higher voltage increased the efficiency.

He told me; “That is nothing.  We just finished hooking up a 5,000 Horse Power electric motor for the air conditioning at the Beasley Auditorium in Pullman, Washington.”

I never saw the motor at Beasley, although I did a lot of work on the college campus.

I also did a job on the Coulee Dam in Washington, and was able to see the huge generators there.  I began to realize that there are huge motors running at various institutions around the world that taxes the imagination.