Trace UL and stupidity [RE-wrenches]

[Rob Wills]

Drake - there are really two sides to this argument:

1/ Islands are unlikely to occur as the probability of a load balance to
+/-10% (otherwise the voltage trips will shut the unit down) is very low..
Also, any low power factor or harmonic loads, especially the distribution
transformer, will tend to drop the island quickly.  This approach is taken
as acceptable by the utilities in Holland.
2/ Islands are pretty easy to create with inverters that do not have active
anti-islanding protection.  Especially with the tuned circuit that can be
formed with power factor correction caps and a distribution transformer.  It
is possible to make inverters that do not have active anti-islanding
protection continue production for as long as the sun keeps up with the
load.

We at Advanced Energy believe that islanding is a problem that must be
properly taken care of.  Utilities do not like to lose control of who can
generate onto their power lines - and they have some justification for this
in that they hold the bag if power quality goes bad. The anti-islanding
issue is a big one for them, for many reasons.  These are mainly line-person
safety, and equipment safety with respect to reclosing the grid onto an
island.

Line-person safety is, as Larry Elliot, pretty much a red herring as the
NESC (the utility's NEC) etc. require a practice of testing and grounding
before working.  There is much more chance of a backfeed from a Kmart
generator and a cord with a plug on both ends..

The reclosing issue is probably more real.

The bottom line is that active anti-islanding technology is available and
works well - it comes down to software techniques that control inverter
power output in response to changes in grid voltage and frequency, that make
an island unstable but are invisible when the grid is connected.  We have a
patent on that if you are interested..

www.uspto.gov  The Patent Number is 6,219,623.

Regards

Rob Wills
VP Technology
Advanced Energy

-----Original Message-----
From: Drake Chamberlin - Electrical Energy
[mailto:solar at eagle-access.net]
Sent: Friday, November 23, 2001 1:02 PM
To: RE-wrenches at topica.com
Subject: Re: Trace UL and stupidity [RE-wrenches]


Wrenches,


These inverters have been getting installed on grid interactive systems for
years.  Have there been any problems?  (Trace-Xantrex doesn't seem to think
so).  Have any linemen been hurt?  Don't the standard safety procedures of
grounding power lines, before working on them, negate any potential
islanding hazard?

The required, lockable utility disconnect switch is supposed to be a fail
safe against any problems resulting from the possibility that an inverter
might not de energize when the grid goes down.  They are theoretically
required as a remedy for this specific issue.  Isn't this a simple
mechanical solution, implemented specifically to address this potential
hazard?

Does anyone know how long an inverter can island under perfect, f"balanced
load" conditions?  How long are such conditions likely to last in real
installations?

Thanks,

Drake

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