IX International Symposium on
Lightning Protection
26
th
-30
th
November 2007 – Foz do Iguaçu, Brazil
SURGE PROTECTIVE DEVICE RESPONSE TO STEEP FRONT TRANSIENT
IN LOW VOLTAGE CIRCUIT.
J.Marcuz S.Binczak J.M.Bilbault F.Girard
LE2I UMR CNRS 5158 université de Bourgogne ADEE electronic
avenue Alain Savary 21048 Dijon, France
PONT DE PANY France
Abstract -
Surge propagation on cables of electrical or
data lines leads to a major protection problem as the number of
equipments based on solid-state circuits or microprocessors
increases. Sub-microsecond components of real surge
waveform has to be taken into account for a proper protection
even in the case of surges caused by indirect lightning effects.
The response of a model of transient voltage suppressor
diode (TVS) based surge protection device (SPD) to fast front
transient is analytically studied, then compared to simulations,
including the lines connected to the SPD and to the protected
equipment.
Keywords: SPD, Surge Propagation, Fast transient, low
Voltage Circuit, protection distance.
1.I
NTRODUCTION
The lightning surges are highly destructive, especially for
the last generation of electronic systems based on solid-state
circuits and microprocessors. These systems work at very
low voltage and are often ground insulated. These advanced
electronic devices have a weak electrical surge withstand
capability, therefore surge protection devices are widely
used to protect electronic systems.
It has been shown that sub-microsecond rise time is possible
in subsequent return strokes [1], whereas building wiring
does not always have sufficient damping effects for steep
fronts [2] induced by close subsequent strokes, and can even
imply overvoltages due to inductances. Therefore, for
proper protection against steep front transients, surge
protection devices (SPD) with extremely short time-
response are needed nowadays. In low voltage power
distribution systems, setting up SPD on the distribution
board prevents side effects in the installation, avoiding the
flow of surge currents in the branch circuits. But the way of
setting up the SPD and especially the inductance of long
connections to the protected line or to the grounding system,
degrades SPD performances. Moreover, the length of
connecting cables between the SPD and the load can
produce reflection and resonance. These phenomena can
increase the voltage at the load up to twice the protection
level at SPD connection point notably for fast front
transient.
In this paper, an analytical study has been carried out in
order to define the behavior of SPD under fast front
transients. The analytical expressions have been compared
with an electromagnetic transient simulation program
(EMTP) for validation. In section II, we will consider the
SPD between two infinite or matched lines. In section III,
the influence of the load and line length is investigated. In
section IV, a parametric study is conducted focusing on two
parameters.
2.ANALYTICAL APPROACH
2.1 Modelling
Figure 1 describes the electrical system under investigation,
where the load is the electronic system to be protected and
where the generator models an incoming surge by releasing
fast front transients. In between, the SPD is connected to the
lines and to the earth via cables. Earth is modeled by its
inductance and its resistance [3], in the case of grounding by
rods.
Figure 1: electrical configuration under study.
About the generator, bi-exponential waves will be
considered. Bi-exponential waves are indeed usually
introduced as the normalized waves induced by a stroke.
In the case of infinite or matched lines, there is no need to