On Wed, 18 May 2016 09:29:04 +0100, Chris Hogg wrote:

On Wed, 18 May 2016 09:13:12 +0100 (BST), "Dave Liquorice"
wrote:

On 16 May 2016 21:31:51 GMT, Huge wrote:

What's even more amazing is that with the press of a button
marked
"MAXGEN"[1], it can go from zero to full output in 15 seconds.

I think that's from in sync spinning in air, rather than
stationary.

They keep one turbine spinning all the time in order to provide
"instant" output. I think it's rather less that 15 seconds, too.

The information about the various start times seems to have disappeared
from the web. A turbine on line and using water I should imagine can go
from "tickover" to full chat as fast as the inlet valve can open. As you
say I'd expect rather less than 15 seconds.

The 10 seconds figure I mentioned related to the time it took to open or
close the giant penstock gate valve(s) feeding the turbines.


I wonder how many tonnes of water per second each turbine uses at
maximum output?

At maximum flow to the turbine hall is 60 cu.m/sec. There are 6
turbines, so 10 cu.m/sec. i.e. 10 tonnes/sec. each
http://tinyurl.com/4nj8a9

I get the impression that they can keep them spinning with compressed
air, which reduces the time to full output compared with a standing
start. But whether all of them spin that way, all of the time, I don't
know.

They don't use compressed air to keep them spinning whenever they need
them in 'Hot Standby' running in air. The turbines use the generator as a
motor to maintain synchronous speed so all that is required to change
from motoring mode to generator mode is basically just a matter of
"Turning on the tap" and adjusting the excitation current to raise the
stator output voltage.

This rather neatly avoids the need to synchronise from a standing start
but at a cost of 4MW per turbine. I'm afraid I can't recall whether all
six turbine sets had this hot standby running in air capability or not.
One thing is for certain, the 90MW turbine sets at Ffestiniog had no such
hot standby feature, hence their much longer 60 seconds run up time.

--
Johnny B Good