[time-nuts] 60 Hz measurement party- big sync motors

Will Matney xformer at citynet.net
Mon Jun 27 03:30:57 UTC 2011


I never did set back and think why they used them, but that would make
sense. The new plant engineer they hired, during my time there, talked them
into installing a new power house (air compressor system) in the paint
department. However, he had ordered screw compressors, running on 460 V, 3
phase motors. He was cursed by every electrician on that job over the big
cables that had to be pulled for the current they consumed.

I also wondered if it could have had something to do with the starting
torque of the sync motors over induction motors. Those old compressors had
flywheels on them almost the diameter of the motors that ran them, and it
would take a huge amount of torque to set them to turning, especially when
the compressor was pumping into a pipe full of compressed air. It would be
about like trying to start or run the engine in your car with the tail pipe
stopped up.



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On 6/26/2011 at 10:12 PM Bill Hawkins wrote:

>Will, and the rest of you fascinated by power distribution,
>A big synchronous motor allows its power factor to be changed by
>changing the field current for a given load. The motor can be
>adjusted to look like a resistive load instead of inductive, or
>even capacitive to correct plant power factor. Look it up.
>Industrial power consumers are charged extra for power factors
>less than unity because the distribution system must carry more
>current for the same watts as the power factor departs from
>Induction motors have inductive power factors because there must
>be slip between the rotating field and the speed of the rotor.
>Synchronous motors don't have slip, just phase angle. Zero angle
>looks like a resistive load, yes?
>The compressors don't have to run in sync.
>Bill Hawkins
>(who heaves a nostalgic sigh just thinking about those fine old
> engines of progress)
>-----Original Message-----
>From: Will Matney
>Sent: Sunday, June 26, 2011 1:11 PM
>To: time-nuts at febo.com
>Subject: Re: [time-nuts] 60 Hz measurement party
>I quite like your generator description of "huge rotating lumps of
>copper-ensnarled iron". It brings me back to around 20 years ago, when I
>was a plant electrician at an older railcar manufacturer. They had huge
>open-frame synchronous motors, from around the 1930's, that ran their air
>compressors, and why they used this type of motor is anybodies guess. If I
>remember right, they were rated at around 200 HP, or so, and were about 8
>feet in diameter. The rotor shaft was mounted on huge babbit bearings upon
>concrete pillars, and about 1/3 of the motor sat in a pit in the concrete
>floor. I used to have to repair the brushes on the slip rings constantly,
>until I talked the boss into adding a shunt across the n.o. contacts on
>250 Vdc contactors to quench any arcing. The motors stator itself ran on
>4160 Vac. Would the other compressors have to run in sync somehow, as all
>of them had these motors, just some a little smaller than the others? They
>drove large single cylinder compressors that fed something like a 6 inch
>air line (pipe). However, they all did not run at once, and they only did
>when there was a larger demand for air. Timing is the only thing I can lay
>this to, and was wondering about it.
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