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

Bill Hawkins bill at iaxs.net
Mon Jun 27 03:12:02 UTC 2011

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 the
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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