CAT3616 with Woodward 2301A; paralleling to grid without governor droop enabled 1

[Mechkane]

I recently started working with a 1990s vintage CAT3616 genset(with Kato generator) that includes PLC-5 controls; I'm trying to come up to speed with this system (no pun intended) and all the fancy accessories they added in the 90s. It has a EGB-29P and 2301A (low voltage model); a KCR-760 (Kato) Voltage regulator, a VAR/PF controller (Basler) set to PF control, SPM-A, Excitation limiter, and a Woodward Load pulse sensor unit. Need I say more..
This genset is only used for backup emergency type power and only is tied to the grid for testing periodically. So testing tied to the grid is 99.9% of what we do with this genset.

I'm more familiar with non PLC Gensets with a 2301A that will enable droop when paralleling with the grid. I was shocked to see that the droop contact (14) on this CAT setup will close when the PLC sees we are tied to the grid versus what I'm more familiar with. (PLC sends signal to a Potter/Brumfield socket relay, which one of its contacts is the aux droop contact for the 2301A) (another set of contacts does put the Voltage regulator in droop).

I would have thought being in Isoch tied to the grid would be bad. I first thought the relay contacts for the 2301A were incorrect.
The 2301A terminals 10/11 show to go to a OFE1 (Analog output Voltage type PLC card). I thought initially that this was a useless connection since those terminals 10/11 are disabled in Droop mode.
I then read in the Woodward manual for the 2301A (Manual 82389_CAT) that includes a small section that included "when running a single unit on an infinite bus with a generator loading control or Import/export control, terminal 14 must be connected to terminal 16 (i.e. close the droop contact) to connect the load matching circuit to the load-sharing lines. The load-sharing lines must be wired to the generator loading control or Import/export control". I'm assuming the PLC I have is the "Import/Export" control? The PLC logic for sending a Block trans write to the Analog PLC card...and to the 2301A is very slim...
I saw in other forums that Woodward 26260 manual was a good reference, so I checked it out. But I'm scratching my head on comparing its terms to what I have installed?

Does anyone else have a similar setup/ or experience with this setup?

 

[davidbeach]

I think the biggest reason for the "test" is to get the prime mover hot and keep it hot for some period of time. Bring it on, run it up, and park it there. That's the bee's knees for the prime mover. That's how something around 100MW of customer standby generation in our DSG program gets exercised every month. And when we run the DSG in response to system contingencies that's exactly what we want, a known output; not an output that varies around.

The more sophisticated owners also have what's known as "Storm Avoidance" mode where the generation comes on, parallels with the utility, adjusts the output to the point that there's no flow across the separation point and then opens that separation point and then goes into load following mode, which is droop. That's a different test, but that allows the testing of the generator controls (prime mover and the generator are already tested), to see that load following, droop or otherwise, also works. Load following without doing a drop and pick.

But my guess is that a regular (near) full load soak test is going to find many more problems with the prime mover than it is with the generator so the get it hot, run it hot, approach provides a more meaningful test of the overall system than a load following test where the load to be followed is essentially undefined. Running it in droop or some other load following scheme at light loading (the overall system doesn't really need that contribution at the time of the test) means less than parking it at 90-95% maximum output for 30-60 minutes.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[waross]

Thanks for the explanation David.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[catserveng]

I'm coming in a little late to this, but what you have was a fairly common load control system on older units like yours. We put many systems into service on 3500 and 3600 series engines with PLC's managing kW load control into 2301A's.

The PLC analog output should be providing a 0-3VDC signal going into the load share lines input of the 2301A, the PLC program should be doing calculations using kW input info from a transducer (preferred) or in some cases the 2301A's load signal output. In some cases the load reference came from an operator display, using a Baseload setting, or in more complex systems a kW transducer provided a signal across a point in the system used to manage import/export control.

To give you really good answers I would need some more details about your system, but what you describe for your real power load control was done in both multiple unit island mode systems and in units tied to larger grids in parallel, mostly in baseload applications.

MikeL

http://www.pactectric.com

 

[Mechkane]

Thanks all for the responses to date.

catserveng; Thanks for the information. Yes the PLC analog output to the 2301A load share lines is from a 1771-OF1 (VDC analog output); the KW input to the PLC is a Crompton Instruments / Paladin Transducer TYPE 256-TWMU. A magpickup is used for feedback, and a MOP is used for speed trim.
Primary control is from a remote (onsite but not in the actual engine room) location via a touchscreen (Windows NT PC with InTouch software) where fiber optic transceivers are used to relay the signal to the PLC. From what I can tell, the touchscreen was built with visual features, and in the case of showing Operators 3 main things for KW: User demand (what the Operator wants for KW), PLC load(what the PLC is actually sending, shown in KW), and KW display (which is from the same paladin transducer). The PLC logic refers to the User demand as "loaddemand" and the PLC load as "loadset". I guess this is just how they decided to "name" them in the logic. To enable load sharing of the 2301A, the PLC logic is looking for breaker closures (essentially if we parallel to the large grid). And if so, a separate DPDT relay is energized and Closes the CB Aux (terminal 14) contact to put the 2301A into Isoch mode.

About 10 years ago (before my involvement in this system) the 2301A was replaced. I looked back at the systems trends to compare their setup/testing of the new 2301A to how the system responded. It appears they were following a standard setup of the 2301A to an infinite bus. This entailed setting both droop and load gain pots full CW, tying to the grid, raising KW to match MOP output voltage that was previously measured while running unloaded with speed raised, to achieve "3% droop". Then, droop was adjusted until 6.0VDC load gain voltage was measured. I don't believe they understood isochronous load sharing at the time as they noted that droop pot adjustments on the 2301A wouldn't result in any change in KW; I'm not sure if they actually measured 6.0VDC load gain voltage. And then they adjusted the load gain pot to reach full load 4400KW. With all this performed, they shut the engine down. A subsequent loaded run (parallel to grid) showed a discrepancy on the Touchscreen, where user demand & plc load did not match the KW indication. user demand and Plc load matched but actual KW (via the transducer) was reading higher. The log shows they "adjusted generator bias" until actual KW indication matched the user demand &plc load. I'm assuming this "generator bias" was adjusting the 2301A's load gain pot.

This got me questioning the actual isochronous load sharing setup as I had never experienced this setup before. I better understand the PLC 0-3 VDC signal, which I'm assuming is 0 to Full load in KW terms? Is this a linear relationship.

I'm rambling at this point. I can add more detail if necessary. Thanks again for any input!

 

[catserveng]

I am traveling today, but when I get home tonight I will see if I can dig up a setup procedure for the controls you are using. You description of your system is very similar to what I have worked with in the past.

Can you share where you are and what the site is? There is a pretty good chance that either me or one of my old cronies may have originally commissioned the unit and helped setup the controls. In that case I might be able to dig up records of the original install work.

Your comment about the 2301A change is telling, in many cases the "old" 2301A would fail and someone not familiar with the initial setup would install a new governor at default load gain setting. To properly work for load sharing/control the load gain needs to be properly adjusted, probably why you see the discrepancy between your desired and actual kW. The Droop pot should be fully counter-clockwise in this case. And the load gain adjusted to provide as close to 6 VDC at full load as possible. It is unlikely that fully CW is correct due to your CT and PT ratios. And sometimes we couldn't get 6VDC so we used a setting as high as we could to get load control stable with good range. Every site was slightly different, but as you work thru these systems the basic setup procedures are the same.

You should also be aware that the 2301A is a single dynamic governor, so the gain, reset and compensation settings will be a compromise between best standalone stability and transient response and paralleled with grid stability. Most systems of that type have long been upgraded to 2301D or E model governors with dual dynamic capability for best stability and transient response in both modes of operation.

Regards, MikeL

 

[Mechkane]

Thank you catserveng. In Arkansas. It's the only 3616 setup in Arkansas (from what I've been told). I was told Southworth-Milton supported the install if that company sounds familiar. There is a brief mention in some older correspondence with CAT. The CAT person was A.Ford (maybe Alan?) and Southworth-Milton's individual was D.Plaster. All of this was installed in the 1994'ish timeframe. I could maybe dig up more information if needed. Thanks again!