[time-nuts] Features of a Precision Clock?

[Dr Bruce Griffiths]

Bill Hawkins wrote:
> 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.
>
> Regards,
> Bill Hawkins
>
>
>
>
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>   
In NZ power generation is predominantly hydro with some thermal 
generation and small amounts of wind generation.
Consequently response to load fluctuations can be somewhat faster than 
when purely thermal generation is used.
The frequency is usually held between 49.9 and 50.1 Hz.
However when generating capacity is lost the frequency will drop well 
below 49.9Hz.
Operation for more than a few seconds below 95% of design frequency can 
severely damage some modern thermal generating plant.

Another reason for avoiding very long AC transmission lines is the 
reactive current flowing in the cable shunt capacitance may exceed the 
load current, especially in non air insulated cables,. this reactive 
power increases the resistive losses in the cable.

Bruce