Street lighting The challenges of surge protection
Outdoor Lighting
White paper
Street Lighting
The challenges of surge protection
The need
for protection
Voltage surges have a huge destructive impact upon public lighting
systems. They wear out LED drivers and distribution panels prematurely,
and increase service interruptions to street lighting. Beyond material
damage to the luminaires, voltage surges caused by lightning, for example,
can trigger or break protective devices in the circuit boards of street
lighting distribution panels. So as well as the cost of replacing hardware,
the public is left without lighting — a critical safety issue in the case of
pedestrian and traffic tunnels, road signs and other public lighting.
The vulnerability of electronic lighting systems to overvoltages is widely
recognized in technical literature, and different European regulations and
standards specify the need for lighting protection. This white paper
explains the causes of lighting overvoltages and how they affect public
lighting installations. It also covers the legal and regulatory framework
governing protection, and proposes a solution to maximize protection
performance and continuity of service.
Public lighting installations are exposed to
the environment. Located where continuity
of service is essential, it is crucial that these
installations are protected against lightning
and overvoltages.
Investing a small amount in protection
can extend luminaire lifetime, improve
public services and greatly reduce overall
operating and infrastructure costs.
2
The challenges of surge protection
Building-in protection
What are transient or surge overvoltages?
When analyzing the phenomenon of overvoltages,
we consider surge overvoltages and power-frequency
overvoltages separately. Although they both represent
an increase in voltage above an acceptable limit,
their root causes, magnitude, duration and method of
protection are radically different.
Surge overvoltages are spikes that can reach tens of
kilovolts but last for only a few microseconds. Despite
their short duration, their high energy content may
cause serious problems to equipment connected to
the electricity network — from premature aging to
destruction — resulting in service disruptions and
costly repairs.
Surge overvoltages have two modes of circulation:
common and differential. Common-mode overvoltages
appear between the live conductors and earth:
for example, line-to-earth or neutral-to-earth.
Differential-mode overvoltages circulate between
live conductors: line-to-line or line-to-neutral.
A well-protected luminaire should integrate
protection for both modes.
I/2
Common-mode signal
Vulnerable
Application
I/2
I
Fig.1 Transient “surge” overvoltage
I
Differential-mode signal
I
Voltage surges have several causes. For example,
lightning discharges that directly strike the
distribution line of a building, or its lightning rod,
can induce electromagnetic fields that generate
voltage spikes in nearby lighting installations.
And very long outdoor distribution power lines are
highly susceptible to the direct effects of lightning
strikes, with large currents from the lightning being
conducted in the power lines. It’s also common for
non-weather phenomena to cause voltage spikes
in adjacent lines — for instance, switching inside
transformer cabinets, or the disconnection of motors
and other inductive loads.
Surge overvoltages are voltage
spikes of several kilovolts that last
for just a few microseconds
Return path via
Earth Ground
Vulnerable
Application
I = current
Fig.2 Definition of common and differential-mode currents
Surge overvoltage protection is provided by installing
a protective device (surge arrester) on the vulnerable
line, and connecting it in parallel or in series.
When connected in series, the protection device
acts as a fuse. But when it’s connected in parallel,
the luminaire continues to function even after the
Surge Protection Device (SPD) is damaged. The SPD
will get damaged after weathering a number of spikes
above a certain voltage level. In the event of a surge
overvoltage, the protective device will divert excess
energy to earth, thus limiting the peak voltage to a
tolerable level for the electrical equipment connected
downstream.
The challenges of surge protection
3
Protecting against the effects of surge overvoltages
in public lighting
An SPD acts as a voltage-controlled switch. When the
network voltage is lower than the activation voltage,
the component is passive. On the other hand, when
the network voltage exceeds the activation voltage,
the SPD diverts the surge energy and prevents it from
destroying the equipment. When choosing an SPD,
you need to consider the equipment’s exposure to
the effects of lightning, along with the maximum
impulse voltage that the equipment needs
to withstand.
SPD
Equipment
Fig.3 Working principle of a surge protection device (SPD)
European standards EN 60.364-5-534 and EN
62.305-1 require that protection against these types
of electrical disturbance are to be provided by a
Type 2 SPD. The protection solution is installed
downstream of the main circuit breaker in the
distribution panel circuit board, in parallel to the
main system. So it diverts the energy of the surge
to earth, limiting the voltage peak to a tolerable level
for equipment connected downstream.
To guarantee proper protection of a luminaire,
the distance between it and its protector circuit must
be as short as possible. If the distance between a
protected distribution panel and several luminaires
is more than 20 meters, using a second protection
stage (of Type 2 or 3) is recommended, even if the
protection level of the first stage seems to be
sufficient (see Fig.4).
U
Vloads > 20m
VSPD
Isurge
In general, the most effective approach to protect
large installations of lighting equipment against surge
overvoltages is by cascading multiple protective
stages. Each stage combines the necessary balance
between discharge capacity and voltage protection
level. This way, a first stage (typically a ‘Type 1’ or
‘Type 2’ SPD) provides robustness, thus diverting
most of a spike’s energy, while a second stage
(typically a ‘Type 2’ or ‘Type 3’ SPD) provides
‘fine’ protection. Thus the peak voltage reaching the
equipment always stays below the critical level.
Of the causes of surges mentioned in international
protection standards, the ones most likely to affect
a public lighting system are:
•direct lightning strikes on distribution lines
(conducted through the power lines), and
•lightning strikes near to a building/structure
(creating induced surges).
4
The challenges of surge protection
t
Fig.4 Effect of cable distance on the voltage protection level
Practical approach
Fig.5 Circuit protection solutions for luminaires and street-lighting
distribution panels
Inside the luminaire
Inside the panel
Stage 1: Standard protection at luminaire level
IEC61547 states that all luminaires should be
protected from overvoltages up to 1 kV in differential
mode and 2 kV in common mode. However, Philips
has decided to exceed these requirements. All Philips
luminaires have a minimum protection of 4 kV, in both
common and differential modes. This level ensures
acceptable protection for most European streetlighting installations, and therefore makes all Philips
luminaires suitable up to Class 4 installations
(as defined in EN61000-4-5).
Stage 2: Additional protection of luminaires
When designing installations, the area should be
assessed for its vulnerability to lightning strikes. If the
vulnerability is high, 10 kV protection is recommended.
In these cases, Philips recommend the use of an SPD,
in addition to the standard protection at luminaire
level to ensure a higher level of protection (10 kV).
This solution will be offered to Philips’ customers
upon request.
Stage 3: Distribution panel board protection
In the most vulnerable environments, the V-check
4RC solution offered by our partner Cirprotec can be
installed on a DIN rail of 4 modules. It protects not only
surge overvoltages (max surge current of 40 kA) but
also power-frequency overvoltages. Power-frequency
overvoltages are often caused by insulator breakdown
in circuitry.
The V-Check 4RC automatically reconnects the power
supply after the surge has finished.
www.cirprotec.com
The challenges of surge protection
5
© 2014 Koninklijke Philips N.V. All rights reserved. Philips reserves the right to make changes
in specifications and/or to discontinue any product at any time without notice or obligation
and will not be liable for any consequences resulting from the use of this publication.
www.philips.com
www.lighting.philips.com
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