[RE-wrenches] 690.47D (revisited)

[Joel Davidson]

Hi Don,

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: I2P at aol.com 
  To: re-wrenches at lists.re-wrenches.org 
  Sent: Saturday, June 06, 2009 11:27 AM
  Subject: Re: [RE-wrenches] 690.47D (revisited)


  In a message dated 6/5/2009 4:31:43 P.M. Pacific Daylight Time, kelly at whidbeysunwind.com writes:
    Mark,
    Yes, it's confusing. Which is why I wanted to know what the Wrenches are
    actually DOING in their installations to meet 690.47D.



  On a ground mounted array using a driven rod I connect it to the system ground ( bonded). Sometimes a driven rod at the array is not required. As to whats the best lightning protection, no actual data one way or another.

  Don Loweburg


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