[RE-wrenches] Three-Phase Generator feeding Series/Parallel Quad Stack

[Phil Undercuffler]

William, I believe you're right about the 180 degree / 120 degree differential. This is similar to the condition that fried the input relays on a handful of XW inverters which were connected to 120/208 three phase inputs.  In fact, Xantrex published a technical bulletin about the issue, available at http://www.xantrex.com/web/id/246/p/docs/pt/18/product.asp

To quote, "Input power ... cannot be simply derived from a phase or line voltage of a three phase 208:120Y or 240VΔ AC source. Instead of cancelling each other as they would with a split-phase source, each 120° out-of-phase leg effectively creates a short circuit (limited by the impedance of the transformer and the wiring), which leads to very high currents flowing on the neutral line causing imminent failure of the inverter's AC relay board."

The bad news is, Classic Stacking won't solve the problem; Classic is limited to two inverters max, and this installation is a quad.  I'm also not sure whether the excessive current flowing on neutral issue would be resolved with the elimination of the transformer, and whether the problem would then just move upstream to the next weakest link, the input relays of the FX.

Xantrex's solution in that technical bulletin (big transformer taking off 1 leg of 3 phase service, converting to 240v) obviously won't work to balance the generator, nor will parallel stacking the quad stack.  I would look into rewiring the genset for 120/240v output, or go hunting for three phase converters.

 
------------------------------------------------------------

Phil Undercuffler
Director, Battery-based and Off-grid
Conergy, Inc.
Our World is Full of Energy
 
1730 Camino Carlos Rey Suite 103
Santa Fe NM 87507 USA
Office | 505.216.3841
Fax | 505.473.3830
www.conergy.us

------------------------------------------------------------ 
-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of William Miller
Sent: Tuesday, July 29, 2008 9:30 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Three-Phase Generator feeding Series/Parallel Quad Stack

Nick:

Here's my best guess:  The X240 is configured to work with power legs with 
180 degree phase differential.  A 3 phase source has 120 degree phase 
differential.   This 120 degree phase differential shows as some degree of 
direct short to the source.

Solution:  I would forego the X240 and change the stacking configuration to 
Classic stacking.  Eliminate any shared neutrals to avoid neutral over-current.

William Miller


At 08:09 AM 7/29/2008, you wrote:
>Hello good folks in the RE world! An off grid customer of mine has a VFX 
>Quad Stack wired exactrly like page 20 in the FX manual, including the 
>X-240 balancing transformerconnected to the panel output legs. He has been 
>feeding it with two legs of a three-phase diesel generator. IS THIS A 
>COMPLETE NO-NO??? HE KNOWS THAT IT WILL RESULT IN AN UNBALANCED GEN 
>OUTPUT, BUT SO FAR IT HAS BEEN WORKING OK, BUT WITH THE FOLLOWING GLITCH: 
>WITH THE GENSET OFF------THE OUTBACK POWER PANELOUTPUT BUSSES ARE BOTH 
>ENERGISED ONLY WHEN THE x-240 BREAKERS ARE ON. AS SOON AS THE GENERATOR 
>STARTS (AGS SYSTEM) THIS 20 AMP DOUBLE BREAKERSEE PAGE 20, X-240) TRIPS 
>IMMEDIATLEY, LEAVING HALF THE LOADS WITHOUT POWER (NO OUTPUT FROM THE LEG 
>2 INVERTERS TO THE HOT 2 OUT BUSS) i'M BAFFELED, COULD SOMEBODY PLEASE 
>EXPLAIN THIS SITUATION TO ME SO THAT i CAN HELP THEM OUT? Another 
>electrician told them that a buck/boost transformer (on the gen 
>output?)would be the fix. Thanks a bunch in advance for your help in this 
>serious matter. Nick Houser Off Grid Services, Powell River, BC


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