Specifications

T4.45
Surge arresters
Overvoltages and dito protection
All electrical and electronic devices on the market are
normally designed according to the applicable
standards. According to these standards (the normal
operating voltage and the applicable creepage
distances) the equipment and the installation must be
able to withstand against a certain voltage, without
being destroyed. In general, this voltage is called the
br
eakdown voltage and is equal to several times the
normal operating voltage.
If the device is hit with a voltage above this
breakdown voltage, no guarantee is given for the
normal operation of the device and no guarantee is
given that afterwards the device will still work
properly. In the majority of cases where a device or
installation is hit with a so-called over
-voltage, the
device or installation is completely ruined and
becomes extremely dangerous towards the
environment.
To avoid these severe surges from travelling
through the installation, and destroying all
connected devices, SurgeGuard SPD’s should be
installed.
The voltage at which an SPD clamps to is known as
the protection voltage
Up (see below) and should
always be lower than the breakdown voltage of the
device or installation that is to be protected. Table
2 summarizes the 3 main categories of equipment
with their respective protection levels.
Terminology
Before going into more detail in technology matters,
this chapter clarifies most of the SPD-related
terminology.
I
MAX
Is the maximum current the SPD can carry (deviate
to ground). According to the standard, an SPD
should be able to carry this current at least once.
Class
The Class of the SPD defines the amount of energy
the device is able to deviate towards the protective
ground. As surges are impulses, and since the
amount of energy is proportional to the surface
below the curve (see fig.1), the class can also be
defined by giving the rise-time, the time to fall back
to 50% and the magnitude (I
MAX) of the impulse
(see also fig.1).
In order to be able to compare different devices,
3 standardized impulse waveforms have been defined:
- 10/350 (Class 1) which has the highest energetic
content,
- 8/20 (Class 2), and
- 4/10 (Class 3) with the lowest energetic content.
Class 1 devices are normally used for front-end
protection, i.e. for high-energy deviation coming
from direct lightning strikes whereas class 2 and
class 3 devices are used at a lower level in order to
reduce the residual voltage (U
P) as much as possible.
U
P
The protection voltage or residual voltage (UP) is the
voltage to which the SPD clamps when it is hit with
a standardised impulse waveform for its specific
class, with a magnitude equal to I
NOM.
I
NOM
Is the current that the SPD can deviate (minimum
20 times). This current is of course much lower
than I
MAX.
T4
UP=2.5kV
Electrical control devices
(i.e. wiring devices),
motors, transformers
UP=1kV
PLC’s, CNC-controllers,
personal computer,
computer network, fax,
modem, hi-fi, VCR, TV,
alarm system, medical
scanning and monitoring
equipment, ...
fig.1
Solutions
Temporary
Uninterruptible or standby power supply (for outages of about 15 minutes)
Motor generator set (for outages of very short duration only)
Long term
Standby generator
Computer or equipment relocated to a different electrical circuit
Voltage regulator
Power line conditioner
Uninterruptible power supply
Motor generator
Surge suppressor
Power line conditioner
Motor generator
Isolation transformer
Power line conditioner
Motor generator
Uninterruptible power supply
Loose wiring and grounding problems corrected
Electrically separate loads that cause harmonic distortion
Power line conditioner
Uninterruptible power supply
Motor generator
Oversize electrical equipment so it does not overheat
UP=1.8kV
Appliances (dish-washer,
laundry machine, freezer,
refrigerator, hot, …)
Protection levels (table 2)