Control.com - Nerds in Control

We have two French assembled GE frame 6B combustion turbines and are in need of any information on the company providing the inverters, AEES out of France. (Web site was no help, contacting them was equally of no help.) The inverter is a MOS 125-115 100VA. GE is no help, maybe it is just me. If any one has ANY info I would appreciate it, Thanks.

maf @ dairynet. com

What is the issue you are having with the inverter(s)? Is it just being used as a UPS for the control system? Does it also power the ignitors during black start?

What is the application?

Our primary inverter is a MOS 125-230/240-1500-60HZ unit with a static bypass switch. We have another one that powers the ignitors for Black Start. It runs off 110 vac and 125 vdc inputs depending on the need, i.e. black start. Both are manufactured by AEES.

Okay, the first thing you need to realize is: Not every unit is supplied with an inverter; or, fewer still are supplied with two inverters. You still haven't told us:

1) what the main inverter does (or what the secondary inverter does), and

2) what is the problem (or what are the problems) you are having with it (the main or the secondary inverter)?

One of the problem with inverters supplied with GE-design heavy duty gas turbine packages is that they are incorrectly applied. (Actually, I have seen this more than 20 times over a career spanning more than 20 years in the combined cycle industry.) Industrial inverters usually have an output labeled "Normal" and one labeled "Alternate" or something to the equivalent. The "Normal" output, which is when the inverter is supplying the load, is really the "Alternate" output (since the inverter is to be supplying the load when the station AC is not available). So, if the inverters are configured such that the load they are supplying is constantly powered by the inverter output, instead of the load being supplied only when the station AC is unavailable, they are frequently (and incorrectly) accused of having problems and/or of failing prematurely.

Think about it: The purpose of an inverter is usually to act as an emergency power supply (an uninterruptible power supply, or UPS) n the event that the normal, station AC is not available. That would mean that they would have to be configured so that the "Alternate" output (the station AC) is normally connected to the load and that in the event of loss of station AC the inverter would supply the load--which "seems" opposite to the naming convention used on the inverter outputs.

So, how is your inverter being used: As a UPS? Is it configured to be normally supplying the load or to supply the load in the event of a loss of station AC?

Let's just say the inverter is properly connected (it's output is only enabled on loss of station AC), and you are experiencing problems with it. If you can source a UPS that has the same ratings, you could use that instead.

Now, there is another interesting group of GE-design heavy duty gas turbines with Mark V turbine control systems (but you've never said you have Mark Vs, have you....) and which use AC-DC converters called <DACA>s to provide the power to the Mark V. I've seen a couple of these units which have inverters supplying <DACA>s which are powering the Mark V--and a 125 VDC battery is *not* connected to the turbine control panel. There are redundant <DACA>s, but no 125 VDC battery power connected to the Mark V. This is insane. Who *needs* to keep their turbine control panel running in the event there is no 125 VDC battery to power the Emergency L.O. Pump motor? In other words, if the 125 VDC battery, which is normally used to supply power to the Emergency L.O. Pump motor, fails and is not available to power the Emer. L.O. Pump, what's the point of keeping the turbine running? If the turbine trips, and the Emer. L.O. Pump is not available because the 125 VDC battery has failed, it's pretty likely that the bearings on the turbine, the Load Gear, and/or the generator are gonna be wiped (destroyed) as the unit coasts down to zero speed. But, these units will be able to watch the unit coast down--because they have inverters (assuming they are working) to power the AC-DC power supplies for the turbine control panel and the operator interface (<I> or HMI), and presuming they have T/Cs in the bearings, they will be able to see the temperatures increase as the bearings fail due to lack of L.O. because the turbine control panel didn't trip the unit when the battery failed.

Pretty neat, huh? Think it can't happen? It *HAS*! That's right--no 125 VDC battery to power the Emer. L.O. Pump, but because the turbine control panel was powered by an inverter instead of the 125 VDC battery the turbine continued to run. A transformer fault caused the turbine to trip and the unit came down on the main L.O. pump, which loses output flow and pressure below about 50 RPM, when it's needed most, and there was no Emer. L.O. Pump running. Frame 6. Wiped the turbine bearings, the load gear bearing, and the generator bearings.

Now, this is *not* a GE-recommended configuration--but some Customers, and their consultants, have demanded it and written it into their contracts and it has been provided. But, it is dangerous, and some would say even, well, less than smart or prudent.

But, we still don't know what the main inverter does at your site, or how it's configured. But, from the sounds of it, if you have more than one inverter this might be something like how your site is configured. *Typically* when a site is configured for black starting, there is only one inverter, to supply a single operator interface *and* the spark plugs (ignitors) during starting. If there are two inverters, then usually one supplies the turbine control panel through <DACA>s, and the second supplies the operator interface and the spark plugs.

There were actually a couple of sites which used inverters to power the turbine control panel through <DACA>s *in addition to* to the 125 VDC battery, though why that was done is still not understood since the units didn't trip on loss of 125 VDC battery. In such cases, if the inverter (or inverters, since at least a couple of sites had multiple <DACA>s) were configured properly, they wouldn't be supplying power *unless* the 125 VDC battery had failed (in which case the turbine shouldn't be running anyway!).

So, we need more information about what the two inverters do at your site, and how they are configured, since most industrial inverters have an internal switch that can be configured to pass station AC to the load and transfer to inverter output in the event of loss of station AC. You are correct; the inverter manufacturer's website has little to no information available. It would also be helpful to understand what the static bypass switch does (when it operates, and what it switches).

AEES seem to be based near me in Lyon, France. The email address for their service dept. is sav@aees.fr, the website is http://www.aees.fr

Steve
www.mtl-inst.com