Record events and lock out generator

Hello, hoping someone may have some advice to lead me in the right direction. I have three generators at a run of river hydro plant. The third unit is the smallest and cycles on/off the most depending on flows. Problem is that at certain flows the 3rd unit will come on line for ~10 min then go offline and continue to do this for anywhere between 1 to 8 hours causing lots of wear and tear on the breaker and other equipment.

What I would like to do is lockout the generator after 2 events. Not sure the best way to accomplish this.

New to the PLC world so any help would be most welcome.

HK

Attached is screen shot of the unit 3 trend.

What I would like to do is lockout the generator after 2 events. Not sure the best way to accomplish this.

Click to expand...

Hello HQK and welcome to the PLC forum.

If your generator #3 is controlled by a PLC program, then it COULD be as simple as creating a counter in the program. If the new counter counts to 2 for 2 startup events within a certain time period, then "lock it out". Most probably there will be complications, being a little familar with hydro. Most likely you will need to look at some other factors such as the river flow rate, the time of day, and if the other generators are running. But all these factors can probably be added to the trigger rung for the counter.

To get detailed, we would need to know the PLC brand, model, and maybe the parts of the program that control the starting of the generator.

GE plc w/ 364 CPU. Attached is the logic for generator starting.

We have to modes for the generator, manual and auto (demand control)
In demand control it looks at head level and starts and stops gens based on that (for the most part). Typically the on/off events last no more than 20 min. I was looking at using breaker closure to start a timer and then a counter to 2 events then lockout. Not exactly sure how to use the timer.

thanks

HK

There are a lot of interlocking devices in that program. The hard part is determining how to inhibit the generator.

I think you need one 20-minute timer "A" that starts at breaker closure. If there is a Stop event before timer A times out, then we Count 1 on a new counter, and reset the timer. If the Counter reaches 2, then we inhibit the generator auto-start from starting again (perhaps by activating a new "HYD3 S/D HOLD" Relay M01325-A to be added on page 10, after rung 28). This relay would have a contact added to the "HYD3 MASTER S/D HOLD" M01326 on rung 29.

The big question is inhibit a new auto-start for how long or until what?

You could use a second timer "B" that keeps the inhibit relay active for a set time period, with a manual override if the system is switched to manual control.

Maybe some of the GE experts will join in with the GE programming software and help you modify the rungs.

It seems that it might be easier to attack the problem from the other end, the thing that causes the on/off cycles. If the cycling always occurs at a known flow rate of water, can that flow rate somehow be measured or anticipated, and the inhibit relay activated before the generator even makes 1 on/off cycle?

I agree that going after what causes the cycles could be easier and in the long term better (whenever the hydro is not running the diesels are, at $5/gal it adds up fast).

The main cause of the cycling is when the waterflow is just enough to keep the head level at set point (10.9 ft) but it cannot keep up with the added demand of another generator. I am going to do some testing to see how far down we can draw the head level and still keep the units online (has not been done before). Right now if the head level falls below 10.75' it kicks the most recently added generator offline, hence the cycling at certain times.

I appreciate the help. Now its time to leave it alone for a while and go smoke a pork belly for tomorrow.

HK

Right now if the head level falls below 10.75' it kicks the most recently added generator offline, hence the cycling at certain times.

Click to expand...

You could add logic to the program that looks at the head level. Use a comparison instrction that says "If Head < 10.75, inhibit Hyd3 Start". But it is really a complex problem because the incoming water flow rate changes constantly, the generator load changes also, and if the flow rate is increasing rapidly after a rain, then 10.75' might even be okay. I guess you could start with a simple comparison instruction and add to it as you learn more about how the system responds.

Now its time to leave it alone for a while and go smoke a pork belly for tomorrow.

Click to expand...

Right! Happy Thanksgiving!