From: Joel Davidson <[email protected]>
Subject: Re: [RE-wrenches] Lightning protection system
To: "RE-wrenches" <[email protected]>
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: [email protected] ; 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
<[email protected]> wrote:
From: Drake Chamberlin
<[email protected]>
Subject: Re: [RE-wrenches] Lightning protection system
To: "RE-wrenches"
<[email protected]>
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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