If he's feeding the grid then his frequency and voltage are fixed by the infinite bus. The governor just changes his power output.
Yup.
Basically, we base the output of the generator on the amount of river flow available. This plant is ~400 yards downstream from a lake, which has gates at the outlet, so we (in coordination with the state) set the out flow of the lake based on lake level and expected precipitation forcasts. Based on how much water is flowing out from the lake, we figure out how much we need spilling over the flashboards (plywood held in place by 1" schedule 40 pipes, will describe purpose later) at the dam (usually ~15-20 cubic feet/second) to keep the river level normal between the dam and the tail race (outlet) of the powerhouse. So, right now we are running at about 400kW, so that is roughly 100-120 cfs flowing through the turbines (iirc), with about another 20 or so cfs flowing over the dam (at lower river flows like now), which puts us at about 140-150 cfs going down the river. There are small streams and such that fill the river between the dam and the powerhouse, so aquatic life is not affected by generation, and to keep things looking pretty for the tourists.
At higher flows, say during spring runoff, where there is a much larger volume of water flowing into the lake, river flow will be greater. If I remember correctly, our plant at full power (rated 600kW, but we run about 680-700kW at full power due to service factor) will pull about 150 CFS of water through the turbine. I've seen 700 CFS flowing out of the lake, which means we have to open an additional waste gate, and drop the flashboards to allow a greater volume of water to flow over the dam without bypassing it (very very bad :laughing
. This is all a careful balancing act between keeping the lake from flooding the surrounding area, the plant making $$, and keeping the river flowing appropriately so wildlife isn't effected.
Flashboards (plywood held in place by pipes) are designed to raise the level of the pond to give the plant higher head. Head, in water terms, is the distance between the top of the mill pond to the turbine. This difference in height is what gives the hydraulic pressure necessary to spin the turbine and generate power. The head at this plant is 76' iirc, and the water flows from the dam to the turbine in 2 4' penstocks (pipes, basically). During normal operation the flashboards are in place at the top of the dam, giving us that extra bit of water pressure. During times of high flows, we pull the flashboards before increasing output from the lake, but sometimes there is just too much water pushing against them to remove them. When enough water is pressing against them, the 1" schedule 40 black iron pipes will fold over, the plywood will go down stream, and the dam will then allow a significantly higher volume of water flow over it without over-topping the embankments.
This is all a pretty slow process. River flow is usually pretty consistent except with heavy rains, spring run off, and fall draw down (lowering the lake level in preparation for winter to allow for more room for water in the spring). It's not like the river flow is changing by the minute. We have been at roughly the same river flow for the past month and a 1/2, but once the snow starts melting and flowing into the lake, the output will increase. When we have heavy, saturated, snow like we have now, a good portion of that will not be absorbed by the ground (considering the ground stays frozen longer than the snow), so it will flow into the lake and cause it to rise a few inches a day. Right now we are at about 8.9' of water at the staff gauge by the lake gates, but if we have a really wet spring compounded with the heavy snow, I have seen the lake get up about 13'. When times like that happen, we go WFO with the waste gate, turbine, an additional turbine to pump water to a storage tank, and drop the flashboards. Flows will be in excess of 650-700 CFS, and will flood the yards and such of houses down stream.
So basically Nuzzie, short story long, an operator only has to be at the plant to check it in the morning, do the daily calculations for power generation, revenue, greasing, etc, and once in the afternoon just to make sure everything is running OK. Extra time has to be spent over there changing river flow, maintenance, and if the plant gets kicked offline during a thunderstorm or whatever, but it's not like a guy has to stand there and tweak the power output all the time.
If you guys want to know more, just ask. What I don't know I can ask the boss man. Pretty cool side job, huh? :thumbup:
