# [time-nuts] Line Frequeny Stablity

Bill Hawkins bill.iaxs at pobox.com
Wed Apr 5 14:13:18 EDT 2017

```The rotary generators in a system of connected generators are
synchronous
machines. There is no frequency difference between them, only phase
angle,
and not much of that - if the system is stable.

The ocean liner analogy is correct, as there is only one captain
directing
the ship's course. If each plant set its own power levels it would be
very
difficult to maintain stability, due to the springiness of long
transmission
lines.

A set of connected generators is controlled by regional dispatchers, who
tell their plants how much power to generate in order for the day to
average
out to 60.000 cycles per second. They count cycles instead of measuring
the
frequency. You can count cycles with a synchronous clock.

This becomes less tidy when DC tie lines are used, because inverters
have
to be adjusted to get the correct power flow.

Hope I got most of that right.

Bill Hawkins

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Peter
Reilley
Sent: Wednesday, April 05, 2017 7:42 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Line Frequeny Stablity

Think of it as an ocean liner trying to keep a dead straight course to
it's destination.
It weighs many tons and wind and waves may drive it off it's path but
the captain
can correct for this.   It eventually arrives at it's destination and is

only a few feet
from the dock.

The total rotating mass of all the generators in a network is many times
the mass of an
ocean liner.   The operators do their best to keep them running at the
correct frequency.
Unexpected load changes can cause some divergence, but over time the
average is dead on.

When I installed power plants in the 1970's they has a special "clock"
that showed the
cumulative error in terms of clock time.   The clock had two inputs, one

from the utility
power and the other from some reference, possibly WWV.   Normally the
"clock" was
pointing up at zero and not moving.

If the generator ran a little too fast the clock would move forward.
As the operator
observed the clock moving away from zero he would reduce the plant's
power and the
clock would move backward toward zero.   His goal was to keep the clock
at zero and
not moving.   Thus, your bedside clock was always on time even if there
were temporary
excursions fast or slow.

Pete.

On 4/4/2017 5:28 PM, Thomas D. Erb wrote:
> Thanks for the info.
>
>
> So that tells me how data is recorded - but not how the frequency is
kept stable ?
>
> Is the line frequency now directly tied to GPS clock - with no drift ?
>
> Thomas D. Erb
> tde at electrictime.com<mailto:tde at electrictime.com> / Electric Time
> Company, Inc.
> Office: 508-359-4396 x 117 / Fax: 508-359-4482
> 97 West Street Medfield, MA 02052 USA

```