Hydro Generator in Islanded Mode 1

[CuriousElectron]

Greetings,
Does anyone know if it is typical to run a hydroelectric generator in islanded mode(feeding station service and isolated from the grid). If so, does one have to make sure that the governor system is fully capable of maintaining the frequency on the unit, since the unit would be isolated from the grid. I'm wondering how the governor would be maintaining the frequency with the grid offline(losing the reference point).

Regards,
EE

 

[waross]

It would take exceptional circumstance to run a hydro plant just to supply station services.
It may be difficult to accurately control the very little water flow that would be required for such a light load.
That said, I once ran a 350 KW diesel plant during a shutdown to power a small electric drill.
The diesel governor is suitable for controlling no load speed.

Bill
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"Why not the best?"
Jimmy Carter

 

[dpc]

The governor would operate in droop mode or possibly isochronous depending on the governor. Governors are certainly capable of this. But if you have a large hydro turbine powering minimal station service, flow may be too low to really operate in a stable manner.

 

[low1]

We've done it before in exceptional circumstances, and the results were satisfactory. 100MW-rated hydro unit supplying a megawatt or so of loading between our hydro plant and the associated HVDC converter station. This was a 1 time event to perform tie-ins of a new HVDC bipole. I had my doubts about the quality of regulation, but it was "good enough" for the amount of time required. A few of our plants have small hydro house units that run station service load.

 

[crshears]

I wouldn't say it's "typical" to do this, but depending on the design of the governor system it may be very doable indeed.

Based on my recollections, Ontario Power Generation, the generation successor/splinter entity of the former Ontario Hydro, did have and most likely still does have numerous smaller generators, meaning rated from ~ 1 to 20 MVA, whose hydraulic governors' speed inputs were coupled direct to the turbine shaft via an independent permanent magnet generator [PMG]. Provided the governor's various dashpots, orifices, check valves were properly calibrated, the unit would behave quite well under such a scenario. Some of these plants were even designed to operate this way by having unit station service transformers directly connected to the generator terminals, meaning the unit could run with its main unit breaker open and only supply station service.

There could of course be other issues with the turbine, such as cavitation, and depending on whether the runner was above or below tailrace level the efficiency could well be terrible...then again, if there is a requirement to pass a minimum specified amount of water in order to comply with environmental conditions such as fish spawning beds downstream etc., the sad efficiency would be of minor concern since you could well have to spill water anyway to meet this minimum flow threshold.

I could go on and on, but let this suffice for now.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

The generator has to be controllable at no-load to allow synchronization.
That may b done manually, I don't know.
I would be concerned with the ability of the governor to track load changes accurately at such a minute percentage of the capacity.
When the load is less than the stated accuracy of the governor and load changes are an even smaller percentage, Accurate automatic control may be very difficult.
This aspect of governor action at the low end was mentioned somewhere on the site by one of or automotive gurus as the reason the most cruise control systems will not engage at speeds below about 25 MPH.
Accurate control at the low end is too difficult.
If you have to waste water for environmental reasons it generally goes over the spillway.
It is difficult to pass excess water through the turbine without increasing the frequency.
There are several ways that automatic control mat be achieved for very light loads but this would entail added equipment at the design stage.
Close accurate control with a standard main governor will be difficult.
Designing and adding appropriate equipment at the design stage, not so hard from a control perspective.
The design of the turbine and the results of allowing only a small percentage of design flow to pass, I will leave to the turbine experts.

Bill
--------------------
"Why not the best?"
Jimmy Carter