SW-series inverters hazard? [RE-wrenches]

[Joel Davidson]

Did you all see the UL notice about SW-series inverters?
Does Xantrex have a solution to this problem?

http://www.ul.com/about/newsrel/alert111601.html

ALERT: PHOTOVOLTAIC INVERTERS MAY POSE HAZARD

November 16, 2001 -- Underwriters Laboratories Inc. (UL) is notifying
electric utility companies, installers and authorities having
jurisdiction (AHJs) that Xantrex Technology or Trace Engineering
photovoltaic inverter models SW3512, SW4024, SW4048 and SW5548 may: 1)
support an unintentional island in the presence of a balanced load, when
utility power is interrupted; and, 2) exceed the output current total
harmonic distortion limit.

Results of operational tests recently conducted by UL during field
investigations revealed that SW series inverters may not cease to export
power to the utility grid when power from the grid is interrupted in the
presence of a balanced load. The SW series inverters may continuously
sustain an unintentional island condition under multiple balanced test
load conditions while exporting power at the tested 25%, 50% and 100%
power levels.

Unintentional islanding occurs when a utility interactive inverter
energizes a portion of the utility grid system when power from the grid
is interrupted. Unintentional islanding may create a risk of electric
shock for utility line personnel by causing a utility line to remain
energized when it is assumed to be disconnected from all energy sources.
This islanding condition may also cause damage to utility equipment,
interfering with the operation and or restoration of normal utility
service.

In addition, the SW series inverters' output current total harmonic
distortion may exceed the 5% limit required by UL 1741, the Standard for
Inverters, Converters and Controllers for Use in Independent Power
Systems and IEEE929, the Recommended Practice for Utility Interface of
Photovoltaic (PV) Systems when the inverter is exporting power onto the
utility grid. This problem is most apparent when the SW inverters are
connected to low impedance utility lines.

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