Invert on Demand with an XW6048 Inverter and a 200amp Generac Auto Transfer Switch

pcguy2u

Have begun to implement a long contemplated change of batteries from AGM to LiFePO4 with some guidance from Discover Energy Systems.

In conjunction with that change, I have implemented a wiring scheme that allows the Generac transfer switch to be automatically activated (on demand electro-mechanically) and for the inverter to begin inverting, all depending on the state of the on/off switch, the batteries' state of charge, and the settings of a 24-hour clock timer.

The system works almost as expected; which means it doesn't work like what works when manually engaging the transfer switch.  Let me explain...

1. If the grid goes down, the inverter goes into invert mode automatically.  In invert mode, there is no load (whole house transfer with no dedicated circuits) on the output until the transfer switch is manually thrown.  Has been made to work that way and functions perfectly with no faults or warnings.
2. When the grid returns, the transfer back to the grid happens seamlessly and there is no evidence of, or anomalies associated with the transfer, like digital clocks or tv's/dvrs that need to reboot/reset.

That is still how it is working or can be made to work depending on if the invert on-demand system is being employed/activated at that moment; it overrides the grid down situation.

When I call the on demand invert system to engage no matter what the coincidence/timing of the grid disconnect and the transfer switch activation is, I get fault F29 (Over-voltage anti-islanding fault, caught by the qualification limit, voltage difference between L1 and L2) most every time and F30 (Over-voltage anti-islanding, fast disconnect, 270 V) other times.  The current delay setting for the transfer switch to activate is 2 seconds and and I have tried zero seconds with the same results.  There is nothing to indicate whether the reference is for AC1 or AC2.

The inverter goes into invert mode and continues inverting; at the end of the invert on demand period at which time the transfer switch and grid tie connection are returned to normal positions and after a 5 minute countdown, the inverter returns to "selling" or whatever is appropriate for the moment in time.

Have tried the following variations:

1. Grid tie disconnected from grid tie position and the transfer switch not switched; gets F30. 
2. Transfer switch activated with grid remaining connected - no Fault; as soon as the grid is disconnected (Transfer Switch changed to backup source and T1/T2 (house loads) connected to E1/E2 (utility or backup power source)), F29 (there's a clue here and need more info).

Here is what the Transfer Switch user manual says about the transfer of T1/T2 (house loads) to E1/E2 (utility or backup power source):

In a Generac automatic transfer switch (ATS), the isolation of

E1/E2 (Generator Input) from T1/T2 (Load Output) is managed by the transfer mechanism, which physically moves to connect T1/T2 to either the utility feed or the generator feed, but never both at the same time. 

• E1/E2 (Generator Input): These lugs are directly connected to the standby generator. They are energized only when the generator is running.
• T1/T2 (Load Output): These terminals connect directly to the home’s main electrical panel (or a subpanel).
• Isolation Mechanism: Inside the ATS, a transfer contactor acts as a double-throw switch. When utility power is present, T1/T2 is connected to the utility lugs. Upon power failure, the controller breaks the utility connection and moves the mechanism to bridge T1/T2 to E1/E2, ensuring no backfeed occurs.

Seems reasonable to believe that in this case, there is standing power on T1/T2 bc the device used to trick the inverter into invert mode is to use a contactor to break its grid tie connection to the utility source in the transfer switch, when in all that is apparent, there is the assumption that power from the utility has been lost.  This provides the moment of switching with an instant (make before break) where a backfeed can occur in this case.  The fault remains (red led is lit) during the demand invert period, but disappears when the demand period ends and a subsequent 5 minute countdown ends.  When the on demand invert period ends, the transfer back to the grid happens seamlessly and there is no evidence of, or anomalies associated with the transfer, like digital clocks or tv's/dvrs that need to reboot/reset or other faults.

The above design which uses a normally closed contactor to break the grid tie connection was originally and ideally designed to open the grid connection at the transfer switch.  Unfortunately the availability of a normally closed 200amp contactor was not an item that I could find sans using one not specifically intended for such a project as mine; not to mention costs running into the thousands of $.  Normally closed contacts provide for reduced energy usage in this case; "normally open" contactors in the 200amp range are available and reasonably priced.

Alternatively, the system as designed and how it's currently working could be used as is; it doesn't seem to have any adverse effects and the XW inverter manual suggests that F29/F30 are both "Automatic" which is what I believe is happening.

There are obviously some leaps of faith in all of the above, but I'm hoping that someone can cast some light on this.

TIA, Nick