194 / 336
10/10
Total Solution to Earthing & Lightning Protection |
9AKK106354A3360
10
Electronic systems protection
Introduction
Special product development
Whilst this catalogue focuses on our standard product range
which meets a wide variety of applications, on occasion a
customer will have a special requirement which needs
transient overvoltage protection.
In these circumstances we have the technical capability
in-house to design and propose a specific solution to meet
the customer’s special requirement.
Following our proposal, technical and performance
parameters of the SPD can be finalized, and the special
product manufactured to order.
Special products completed to date include:
–– Low-current supply protection to industrial
microwave ovens
–– Media distribution protection (TV/Radio/DAB on 19” rack)
–– Integrated photovoltaic inverter protection
–– Overvoltage disconnect for battery-charger installations
within substations
For more information about special product development, or
to discuss a particular project, please contact us.
Common terminology and definitions
The following common terminologies, as recognized by
IEC/BS EN 61643, are used throughout SPD specifications in
order to aid correct selection and are defined as follows:
Nominal Voltage
U
O
is the phase to neutral AC RMS voltage
of the mains system (derived from the nominal system
voltage for which the SPD is designed.
U
O
is the voltage by
which the power system is designated e.g. 230 V.
Maximum Continuous Operating Voltage
U
C
is the
maximum RMS voltage that may be continuously applied to
the SPDs mode of protection e.g. phase to neutral mode. This
is equivalent to the SPDs rated peak voltage.
Temporary Overvoltage
U
T
is the stated test value of
momentary voltage increase or overvoltage that the power
SPD must withstand safely for a defined time.
Temporary overvoltages, typically lasting up to several
seconds, usually originate from switching operations or wiring
faults (for example, sudden load rejection, single-phase faults)
as well as mains abnormalities such as ferro-resonance
effects and harmonics.
Impulse Current
I
imp
is defined by three parameters, a current
peak with a charge and a specific energy typically simulated
with the 10/350 μs waveform to represent partial lightning
currents.
This waveform is used, with peak
I
imp
current value stated, for
the mains Type 1 SPD Class I test and typically for data/
telecom SPD Test Category D.
Nominal Discharge Current
I
n
is a defined nominal peak
current value through the SPD, with an 8/20 μs current
waveshape. This is used for classification of mains SPDs
(Class II test) and also for preconditioning of SPDs in Class I
and Class II tests. (Note: within BS 7671,
I
n
is referred to
as
I
nspd
).
Maximum Discharge Current
I
max
is the peak current value
through the SPD, with an 8/20 μs waveshape.
I
max
is declared
for mains Type 2 SPDs in accordance to the test sequence of
the Class II operating duty test. In general,
I
max
is greater than
I
n
.
Combined Impulse Test with Open Circuit Voltage
U
OC
is a hybrid 1.2/50 μs voltage test combined with an
8/20 μs current.
The test is performed using a combination wave generator
where its open circuit voltage is defined as
U
OC
, typically 6 kV
1.2/50 μs for the mains Class III test and up to 4 kV
1.2/50 μs for signal/telecom Test Category C.
With an impedance of 2 Ω, the generator also produces a
peak short circuit current (sometimes referred to as
I
SC
) at half
the value of
U
OC
(3 kA 8/20 μs for the mains Class III test and
up to 2 kA 8/20 μs for signal/telecom Test Category C).
With both voltage and current test waveforms, the combined
impulse test is designed to stress all technologies used
within SPDs.
Voltage Protection Level
U
P
is the key parameter that
characterizes the performance of the SPD in limiting the
transient overvoltage across its terminals. A low protection
level value (also known as let-through voltage) is therefore
particularly critical for the effective protection and continued
operation of electronic equipment.
The peak voltage protection level
U
P
is declared when the
SPD is tested with its stated nominal discharge current
I
n
(or
the peak current (
I
peak
) of
I
imp
) and is also declared when
the SPD is subject to combined impulse test (mains Class III
test for Type 3 SPDs) as well as data/telecom Test
Categories C and B.