2011 EMC Directory & Design Guide - Interference Technology

surge & transients
A Risk A s s e s s m e n t f o r L i g h t ning Prote c t i o n S y s t e m
A Risk Assessment for Lightning
Protection System (LPS)
Bryan Cole
Figure 1. Power quality pyramid.
Technology Research Council
Nichols, New York USA
Many articles, papers, and standards
have been written and/or developed
documenting proper application
of surge protection devices (SPDs),
identification of SPD performance characteristics,
proper SPD safety requirements,
etc. However, there are minimal articles on
describing when an engineer should specify
SPDs to be applied to an electrical distribution
system.
SPDs are installed to protect against
transient overvoltage and overcurrents from
affecting the electrical systems and processes
within a facility. Transients occur from
environmental and human factors. Protection
of the facility, the electrical system and
the processes contained within the facility
are the second most important item to be
considered in the power quality pyramid;
preceded only by grounding and bonding
for the safety of personnel (Figure 1).
There are numerous environmental
causes that can disrupt the facility, the electrical
system, or the processes within the
structure. These factors include hurricanes,
tornados, floods, lightning, etc.
Transients from environmental causes
include those from direct and indirect
lightning strikes. To protect a facility from
lightning induced transients, a lightning
protection system is needed. When protecting
a structure from direct lightning strikes,
standards require that SPDs be installed
whenever a lightning protection system is
installed [1].
In the design of an optional, legally
required standby, or emergency power
system, a risk assessment of the interaction
between environment and human factors is
not mandated by the National Electric Code
(NEC) [2]. In the design of a critical operating
power system, the NEC requires that a
risk assessment be conducted [2]. Even if
not required by the NEC, a risk assessment
of environment and human factors for all
power systems should be considered in the
design or redesign of every facility.
There are many factors to be considered
in the risk assessment. Lightning risk assessments
are described in US and international
standards [2,3]. This article will
focus on a risk assessment to determine
if a lightning protection system and SPDs
should be installed using the National Fire
Protection Association standard on Lightning
Protection Systems, NFPA 780. Annex
L of NFPA 780 describes methods for simplistic
and complex risk assessment. This
article focuses on a simple risk assessment.
LIGHTNING RISK ASSESSMENT
Performing a risk assessment to determine
if the facility needs a lightning protection
100 interference technology emc Directory & design guide 2011