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BETA Protecting
Overvoltage Protection Devices
Configuration
6/28
Siemens ET B1 · 10/2008
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Breaking capacity, follow current discharge capacity
I
fi
The breaking capacity is the prospective r.m.s. value of the follow
current that can be extinguished by the overvoltage protection
device on its own when U
C
is applied. This is proven in the operating
duty test acc. to EN 61643-11.
Break time t
a
The break time is the time required to automatically switch off the power
supply in the event of a fault in the electrical circuit or equipment being
protected. The break time is an application-specific value, which is
derived from the level of fault current flowing and the characteristic
of the protective device.
Categories according to IEC 61643-21 (DIN VDE 0845-3-1)
To test the current carrying capacity and the voltage limitation during
pulse interference, the standard IEC 61643-21 (DIN 0845-3-1)
describes a range of surge voltage and surge current impulses. All
Siemens overvoltage protection devices exceed these values in the
depicted categories. For this reason, the explicit value for the surge
current carrying capacity is derived from the specified rated discharge
surge current (8/20) and lightning impulse current (10/350).
Combined surge U
oc
The combined surge is produced by a hybrid generator (1.2/50 s,
8/20
s) with a fictitious impedance of 2 ohm. The no-load voltage of
this generator is indicated as U
oc
.
The specification of U
oc
is
primarily achieved with type 3 arresters.
Frequency ranges
The frequency range characterizes the transmission band or let-
through frequency of the arrester, depending on the described
damping characteristics.
Insertion loss
At a specified frequency, the insertion loss of a overvoltage protection
device is described by the ratio of the voltage value at the installation
site before and after insertion of the overvoltage protection device.
Unless otherwise specified, this is based on a 50 ohm system.
Lightning impulse current
I
imp
The lightning impulse current is a standardized surge current curve
with waveform 10/350 s. With its parameters (peak value, load,
specific energy) it simulates the load of natural lightning currents.
Lightning and combination surge arresters must be capable of
repeatedly discharging these types of lightning impulse currents.
Limit frequency f
G
The limit frequency describes the frequency-dependent behavior of
an arrester. The limit frequency is the respective frequency that
produces an insertion loss under specific test conditions (
a
E
)
of 3 dB
(
see EN 61643-21). Unless otherwise specified, this is based on a
50
ohm system.
Line-side overcurrent protection/discharge back-up fuse
An overcurrent protection device (e.g. fuse or miniature circuit
breaker) that is located outside the arrester on the infeed side and
serves to interrupt the line-frequency follow current if the breaking
capacity of the overvoltage protection device is exceeded.
Maximum discharge surge current
I
max
The maximum peak value of the surge current with the waveform
8/20
s that the device can safely discharge.
N-PE arrester
Protective devices that are intended solely for installation between
the N and PE conductor.
Operating loss
In high-frequency applications, the operating loss indicates how
many parts of the "advancing" wave are reflected at the protective
device ("transition point"). This is a direct benchmark for how well
suited a protective device is to the surge impedance of the system.
Operating temperature range
The operating temperature range specifies the range within which
the devices can be used. In the case of devices without self-heating,
this is identical to the ambient temperature range. The temperature
rise in devices with self-heating must not exceed the specified
maximum value.
Protection circuit
Protection circuits are multi-step cascading protective devices.
The individual protection steps can be made up of discharge
paths, varistors and/or semiconductor devices. The energetic
coordination of the individual protection steps is achieved using
decoupling elements.
Protection level U
p
The protection level of an overvoltage protection device is the
highest instantaneous value of the voltage at the terminals of an
overvoltage protection device, determined from standardized
individual tests:
•
Lightning impulse sparkover voltage 1.2/50 s (100 %)
•
Operational voltage at a rate of rise: 1 kV/ s
•
Residual voltage U
res
for rated discharge surge current
The protection level characterizes the capability of an overvoltage
protection device to limit overvoltages to a remainder level.
When used in power systems, the protection level determines
the mounting location with regard to overvoltage category acc.
to DIN VDE 0110-1, -11.
In the case of overvoltage protection devices used in information
systems, the protection level must be adapted to the immunity to
interference of the equipment being protected (EN 61000-4-5, -12).
Protective conductor current
I
PE
The current that flows through the PE terminal when the overvoltage
protection device is connected to the rated arrester voltage U
C
without any load-side consumers.
Rated arrester voltage U
C
The highest continuous voltage (maximum permissible operational
voltage) is the r.m.s. value of the maximum voltage that can be
applied under field conditions to the terminals of the overvoltage
protection device as specified on the respective terminal. It is the
maximum voltage that can be applied to the arrester in a defined,
non-conductive state that still ensures that this state can be restored
after it has tripped and discharged. The value of U
C
is based on the
rated voltage of the system being protected and the specifications
of the installation regulations (DIN VDE 0100-534).
Rated discharge surge current
I
n
The rated discharge surge current is the peak value of a surge
current of the waveform 8/20 s, for which the overvoltage protection
device is designed in accordance with a specified test program.
Rated load current (rated current)
I
L
The rated load current is the highest permissible operational current
that can be continuously routed over the terminals with this specification.
Rated voltage U
N
This corresponds to the rated voltage of the system to be protected.
In the case of information systems, the rated voltage usually serves
as the type rating.
In the case of AC voltage, it is specified as the r.m.s. value.
Response time t
A
Response times largely characterize the response behavior of the
individual protective elements used in arresters. Depending on the
rate of rise du/dt of the surge voltage or the di/dt of the surge current,
response times may change within specific limits.
© Siemens AG 2008