[RE-wrenches] Lightning protection system
Darryl Thayer
daryl_solar at yahoo.com
Tue Mar 10 18:51:35 PDT 2009
Thanks Joel
the Lightning and Transients research Institute has been closed, I am sorry to say. The paper is valuable and reassuring, if the module frames are properly grounded, they act as a shield and will protect the PV source and output circuits if they are shielded via conduit or coaxial cable. This also implies the grounding system should be of low resistance.
DAryl
--- On Tue, 3/10/09, Joel Davidson <joel.davidson at sbcglobal.net> wrote:
> From: Joel Davidson <joel.davidson at sbcglobal.net>
> Subject: Re: [RE-wrenches] Lightning protection system
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Tuesday, March 10, 2009, 8:14 PM
> In 1983 Arco Solar and the Lightning & Transients
> Research Institute,
> St. Paul, MN, presented a paper at the Greece PV conference
> titled
> "Ability of Photovoltaic Modules to Withstand
> Lightning Strikes."
>
> Summary: The ability of glass superstrate and metal/plastic
> substrate
> modules to withstand lightning strikes was examined. Each
> of 3 different
> types of modules were exposed to 4 nearby and 1 direct
> strike of high
> voltage long arc simulated lightning (400,000 volts, 10,000
> amps), and
> to 1 direct strike of high current, long duration lightning
> (150,000 to
> 175,000 amps, 50,000 volts). Visual and electrical
> examination
> demonstrated that the high voltage strikes produced no
> electrical damage
> to the glass superstrate modules and little to the plastic
> substrate
> module. The high current, long duration strike resulted in
> varying
> degrees of physical damage to all modules but little or no
> loss in
> electrical performance.
>
> Conclusions: The experimental data indicate that a glass
> front module
> with a rigid metal frame is able to withstand almost any
> lightning
> strike if the frame is grounded to the earth. The metal
> frame acts as a
> grounding rod attracting all the current to it. However, a
> strike which
> breaches the integrity of the encapsulation might, under
> some
> conditions, eventually destroy the module. Data from the
> field appear to
> concur with the experimental data presented in this paper
> but also
> indicate that while the modules survive a lightning storm,
> additional
> protection may be required for the cabling, power
> conditioning
> equipment, and control systems. A grounding rod will
> protect the array
> from direct strikes but further protection is required for
> induced
> voltages and side flashes they can create. Shielding (e.g.
> coaxial
> cables) will protect the wiring. The terminals of the
> balance of system
> components can be protected by the use of nonlinear circuit
> elements
> known as terminal protection devices. These devices may be
> nonlinear
> resistors or varistors, semiconductor junction devices and
> dielectric
> breakdown devices or sparkgaps. The degree of protection
> needed for any
> particular installation will be determined by factors such
> as site
> location, size of the array, safety considerations and
> cost.
>
> Joel Davidson
>
> ----- Original Message -----
> From: Matt Tritt
> To: daryl_solar at yahoo.com ; RE-wrenches
> Cc: trang donovan
> Sent: Monday, March 09, 2009 11:04 AM
> Subject: Re: [RE-wrenches] Lightning protection system
>
>
> Hi Darryl,
>
> Just to see what your take would be, and other's -
> what would the case be should the modules have
> non-conducting frames (or even no frames)is the case with
> some systems on the market?
>
> Matt T
>
> Darryl Thayer wrote:
> Yes the electric power and atmospheric grounding systems
> should be connected together to serve as a larger better
> grounding system. The Electrical code requires that at only
> one point does the neutral (grounded) conductor of the
> electrical power system get connected to the grounding
> system, this is to prevent the grounding electrode system
> from carrying electrical power system currents. The
> electrical power system is to be grounded to prevent the
> electrical power system from differentiating its self via
> the injection of energy from other electric power sources
> including atmospheric electrical energy.
>
>
> The lightening protection system is to create a path from
> the atmospheric energy to the earth grounding system.
> ((Wind rain, dust and friction cause the atmosphere to
> become charged relative to the earth, conducting objects can
> build a charge if not electrically connected to the earth,
> these current flow all the time, although they are small
> sometimes, and in the case of a lightening strike incredibly
> large. Even small currents can build large voltages and
> fail electronic components.
>
> The frames of solar modules are electrical conduction
> components not normally charged that can present a personal,
> and physical damage potential (life-property) if they become
> charged by the electrical power system and therefor the
> underwriters require they be protected by grounding. This
> accidental energy need to be safely returned to the
> electrical power system, and properly this is called bonding
> back to the neutral conductor. This grounding is described
> by the NEC in 690 and 250 primarily. The frames of the
> modules can become charged by atmospheric energy energy,
> this energy needs to be returned to the earth, via the
> lightening protection system, ie grounding electrode system.
> The code says little about this, however, it is addressed
> in 690 and 250.
>
> Sorry I said so much.
> Darryl
>
>
> --- On Fri, 3/6/09, Drake Chamberlin
> <drake.chamberlin at redwoodalliance.org> wrote:
>
> From: Drake Chamberlin
> <drake.chamberlin at redwoodalliance.org>
> Subject: Re: [RE-wrenches] Lightning protection system
> To: "RE-wrenches"
> <re-wrenches at lists.re-wrenches.org>
> Date: Friday, March 6, 2009, 8:47 AM
> I didn't get a reply to the question about connecting
> the GEC to the
> lightning protection system on the 8 story building.
> Although this
> may seem like an intrinsically dangerous idea, a lightning
> protection
> system is required to be bonded to the building grounding
> electrode system.
>
> "250.106 Lightning Protection Systems.
> The lightning protection system ground terminals shall be
> bonded to
> the building or structure grounding electrode system."
>
> It would therefore seem that the suplemental ground could
> connect to
> that system as well, and in fact use the existing
> conductor. Any
> input would be welcome.
>
> Thanks,
>
> Drake
>
>
>
>
> At 09:19 PM 3/4/2009, you wrote:
> Hello Wrenches,
>
> Can the supplemental grounding electrode conductor be
> connected to a
> lightning protection system?
>
> We have a case where it would be difficult to run a GEC
> down a multi
> story building, but have a convenient copper wire, from
> a lightning
> protection system, that runs to a rod.
>
> Thank you,
>
> Drake Chamberlin
> Athens Electric
> OH License 44810
> CO License 3773
> 740-448-7328
> 740-856-9648
>
>
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> Drake Chamberlin
> Athens Electric
> OH License 44810
> CO License 3773
> 740-448-7328
> 740-856-9648
>
>
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