Fw: Wind gennies and code (was Lightning Revisited) [RE-wrenches]

[Allan Sindelar]

Wrenches,
This is John Wiles' response to questions concerning grounding of a wind
tower as a separate structure.
The preceding thread that led to this is contained in the message below.
Allan @ Positive Energy

----- Original Message -----
From: "John Wiles" <jwiles at nmsu.edu>
To: "Allan Sindelar" <allan at positiveenergysolar.com>
Sent: Monday, April 15, 2002 9:24 AM
Subject: Re: Fw: Lightning Revisited [RE-wrenches]


> Allan:
>
> There are many issues associated with grounding wind turbine systems.
>
> 1.  With the exception of the SW Wind Power Air series of wind
> turbines, I know of none that have been through the UL Listing
> process.  This process , to a great extent, ensures that the wind
> turbine can be installed in accordance with the requirements of the
> NEC including proper and safe grounding.
>
> 2.   There are three-phase delta-connected power systems that have no
> grounded conductor.  They still require all metal surfaces (that
> might be energized) to be grounded with equipment-grounding
> conductors.
>
> 3.  The best that I can see with the Bergy product is to follow the
> manufacturers instructions.  These are based on Bergy's experience
> and should not overtly conflict with NEC requirements.
>
> 4.  See 250.4 (B) for grounding ungrounded systems.  See 250.24 (D)
> for more grounding requirements for ungrounded ac systems.  Section
> 250.32 (A) and (C) give the requirements for grounding two structures
> supplied by a common service (the wind turbine).  These (and other
> NEC) requirements need to be addressed in a manner that takes into
> account the location of the rectifier unit.  If on the base of the
> tower, then one set of rules would be applied.  If located remotely
> from the tower, another set may apply.
>
> 5.  With respect to surge (lightning) suppression, what the PV
> industry (including me) does not know would fill many, many volumes.
> I prefer to meet code requirements for grounding and then let the
> lightning and surge control experts take over.  The two systems
> (power and lightning protection) are generally separated except when
> they are in contact (wind towers) and then the NEC has some guidance
> in Section 250.106.  Surge arrestors are covered in NEC Article 280.
> They type and location of any surge arrestors is best left up to the
> manufacturer of the wind turbine and the manufacturer of the surge
> arrestor.  Typically in a three-phase ungrounded delta power system,
> surge protection would be applied phase-to-phase and phase-to-ground.
> Depending on what needs surge protection, surge supression devices
> may need to be applied in more than one location.
>
> 6.  As far as I can tell, the wind turbine power lines appear to best
> be converted (rectified) to a grounded dc power signal at a
> disconnect at or before the point of entry of the building.  A
> disconnect immediately inside the building at the point of entry
> would also suffice.  This would comply with the service entrance
> requirements and the grounding requirements.
>
>
> >----- Original Message -----
> >From: "Allan Sindelar" <allan at positiveenergysolar.com>
> >To: <RE-wrenches at topica.com>
> >Sent: Saturday, April 13, 2002 8:01 PM
> >Subject: Re: Lightning Revisited [RE-wrenches]
> >
> >
> >>  Bill, what you describe is what I would do, and fits as a common-sense
> >>  approach. We do relatively little wind, as our solar resource is so
> >>  reliable, so my opinion isn't based on extensive experience. I'll
forward
> >>  this to J. Wiles and post his response.
> >>  Allan
> >>
> >>  ----- Original Message -----
> >>  From: "Bill Brooks" <billbrooks7 at earthlink.net>
> >>
> >>  > In the three-phase AC windturbine example there is no grounded
> >conductor.
> >>  > All three current-carrying conductors need surge arrestors (probably
> >best
> >>  to
> >>  > mount the surge arrestors both at the tower, grounded to the tower
> >ground,
> >>  > and again at the inverter/controller, grounded to the service
entrance
> >>  > ground). I would discuss this with the inspector, but it seems like
> >having
> >>  a
> >>  > separate tower ground would be okay as long as it sufficient
distance
> >>  > (including guy wires) from the building it is serving. Would you
agree
> >>  with
> >>  > that approach?
> >>  >
> >>  > Bill.
> >>  >
> >>  >
> >>  > -----Original Message-----
> >>  > From: Allan Sindelar [mailto:allan at positiveenergysolar.com]
> >>  > Bill,
> >>  > I see a possible problem with your recommended solution. The
separate
> >>  > structures provision also requires a separate single-point bond in
each
> >  > > "structure" between grounding conductor and a grounded conductor.
On the
> >>  > three-phase wild AC of many wind generators, what would be the
grounded
> >>  > conductor (the equivalent of AC neutral or DC negative)? Have I
missed
> >>  > something here?
> >>  > Allan at Positive NRG
> >>  >
> >>  > ----- Original Message -----
> >>  > From: "Bill Brooks" <billbrooks7 at earthlink.net>
> >>  >
> >>  > > What about employing the grounding of separate structures
provision in
> >>  NEC
> >>  > > 250-32 (2002 code)? If there is a grounded conductor, then that
> >>  conductor
> >>  > > should be grounded at the tower (or PV Array for PV) and at the
> >service
> >>  > > entrance with no ground wire between them and no metalic conduit.
All
> >>  > > ungrounded conductors must have surge protection (Phasor, Delta,
> >>  voodoo).
> >>  > > The main issue is that you cannot touch the tower or module frames
> >while
> >>  > > touch something connected to the house. The inverter, however, is
> >>  working
> >>  > > with conductors that are all referenced to the same grounding
system.
> >>
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> >>
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> >>
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> >>
> >>
>
>
> --
>
> If I can provide further information, please do not hesitate to call,
> e-mail or fax me.
>
> John
>
> John C. Wiles,  Program Manager
> Southwest Technology Development Institute, New Mexico State University
> 505-646-6105      505-646-3841 (FAX)   http://www.NMSU.Edu/~tdi/pv.htm
> SWTDI/NMSU
> 1505 Payne Street-Campus
> Box 30001/MSC 3 SOLAR
> Las Cruces, NM 88003

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