[time-nuts] Features of a Precision Clock?

Bill Hawkins bill at iaxs.net
Sat Oct 7 19:06:41 EDT 2006

Dr Bruce Griffiths said,

"Some generators are kept continuously spinning and
synchronised to the mains but generating little power.
These spinning reserve generators are necessary to
stabilise the grid against load fluctuations, they can
very quickly supply power when required."

I hope you don't mean that the reserve generators supply
power from their rotational inertia. They do, but not
enough to keep the frequency from changing. 

There's another reason for wasting heat. Spinning reserve
is necessary because it takes hours to bring a big turbine
up from a cold start. They have to heat up slowly to avoid
thermal stress in the blades and the big metal bits. The
boiler also has to be hot, but even so it can't change
quickly. "Quickly" means minutes, not milliseconds.

Think of the incredible amount of energy stored in many
rotating generators linked by the synchronous network. If
the load suddenly increased 10% then the rotational energy
removed from the generators would supply the increased demand
at the cost of slowing down. Then turbine governors open
steam valves, causing the boiler pressure to drop, causing
more fuel and water to be added to the boiler. The network
gradually comes back up to speed until the turbine governors
are satisfied, which is not exactly 50/60 cycles.

In fact, this group is liable to lose interest (if any) in
power line frequency when it becomes clear that the system
has no natural frequency. It is not an oscillator whose
frequency is determined by physical properties, like a
piezoelectric crystal or a cloud of atoms. What you are
seeing in the power line frequency is a marvel of coordinated
control systems barely restraining enormous energies.

Since I'm in the control business, I think that's neat. YMMV.

Bill Hawkins

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