[time-nuts] No more 60Hz! TEC Elimination - control

[Bill Hawkins]

Group,

The effort to track power line frequency changes is laudable. I think
the effort to determine the stiffness of the network by measuring the
phase angle between GPS time and local line zero crossings is most
interesting. But the following is about the frequency control problem.

The main problem is that the amount of power that is stored in the
distribution system is negligible. The generating station has no
information about load changes until after they have happened. There
is no lag time that allows derivative action to compensate.

If the generating station is on an island with no connection to any
grid, you can use a proportional controller with integral action to
control the generator speed by manipulating the fuel valve to the
engine. This can hold the generator quite close to your desired line
frequency. But because it is feedback control, an error must be
sensed before the fuel valve moves - cycles can be lost. It is still
necessary to manually bias the fuel valve to match the error between
the cycles generated and the GPS cycles elapsed.

When generating stations are synchronously synchronized by the 
distribution network, a new problem arises. The stations can not all
use integral action and maintain stable control. In fact, only one
integral controller may be on such a network. The integral control
comes from the area dispatcher, who integrates the cycles generated
and compares them to the cycles to maintain 60.000+ cycles per second
(in the degenerate West).

I am not clear on how the dispatcher allocates frequency error to the
area stations, or how they react to commands to change. But it seems
to me that this is a control problem that can be solved without undue
stress on the generating equipment. Perhaps it is as simple as a
setpoint rate of change limit (can't be, 3000 people would have thought
of that.)

We welcome your comments with Enthusiasm.

The references below are important.

Bill Hawkins

-----Original Message-----
On Fri, Jun 24, 2011 at 7:02 PM, Bob Kupiec <bobkupiec at comcast.net> wrote:
>
> AP: Power grid change may disrupt clocks
> -----------------------------------------
> http://news.yahoo.com/s/ap/20110624/ap_on_hi_te/us_sci_power_clocks
>
>
> Time Error Correction Elimination
> ---------------------------------
> http://www.nerc.com/page.php?cid=6|386
>
> NERC Report - June 14
> ---------------------
> http://www.nerc.com/files/NERC_TEC_Field_Trial_Webinar_061411.pdf