Figure 5.8.1.2 h (c)
DEHNbloc® NH
Figure 5.8.1.2.h (b) DEHNbloc ®
Figure 5.8.1.2.h (d) Installation without minimum
distances
Figure 5.8.1.2 h (a)
Encapsulated gliding spark gap
NH-fuse bases size 00 (also in fuse-disconnector blocks). Installation by a usual fuse handle is possible without operational interruption. This is especially attractive for application in industrial plants.
Because of the gliding spark gap technology the ‘breakwater function’ is guaranteed and thus an energetic coordination (as explained in chapter 4.5.4) with surge arresters based on varistor technology, like DEHNguard®, is possible.
DEHNport®, DEHNport® Maxi, DEHNbloc® NH and DEHNbloc®
can be installed upstream of the meter because of the leakage current-free operation and the high insulation resistance.
Another special lightning current arrester (according to E DIN VDE 0675 Part 6/A2) based on air spark gaps is the N-PE lightning current arrester DEHNgap B (Figure 5.8.1.2 i). What is the task of an N-PE lightning current arrester?
Lightning current arresters should be installed as close as possible to the building input. In the TT-system this means an installation upstream of the residual-current device. In the case of an earth fault in this range, the upstream fuse must disconnect. But this is not guaranteed under unfavourable earthing conditions.
On using the N–PE lightning current arrester DEHNgap B in a ‘3 + 1-circuit’, where the three phases (L1, L2, L3) are connected to gliding
spark gaps (e.g., the DEHNport) and a spark gap is installed between neutral conductor N and protective conductor PE (chapter 5.8.1.6), there is a short-circuit current between the phases and neutral conductor in the case of an arrester fault which the upstream fuse can now break in the time provided.
The N–PE lightning current arrester type DEHNgap B can safely conduct the residual current of the incoupled lightning between the earthing system and the neutral conductor up to 100 kA (10/350μs) at a sparkover voltage < 4kV (1.2/50μs).
The compact enclosure design with a space of two modules and the multifunction terminals for clamping both the terminal wires and comb- type bars makes the N–PE lightning current arrester DEHNgap B very easy to use.
Also a quench gap (Figure 5.8.1.2 j) is suitable for the inclusion of power lines into the lightning protection equipotential bonding at the interface of lightning protection zones 0 and 1. It is also able to extinguish mains follow-currents automatically. This lightning current arrester has been proven in practice for years and is included in the standards DIN VDE 0804 Part 2 and DIN VDE 0845 Part 1. Quench gaps are, for example, used in the lightning current arrester arrange- ment described in chapter 6.5 (Figures 6.5 b and 6.5 c) to protect transportable telecommunication facilities and for the connection of the mains supply of TV transmitters (chapter 6.4, Figures 6.4 e and 6.4 f, b).
5.8.1.3 Surge arresters for protection of permanent installation, class C
According to DIN VDE 0675 Part 6, class C surge arresters are used in the permanent building installation.
At lightning protection zone interfaces 0B/1 and higher, the phases (L1,
L2, L3) of the mains are equipped with surge arresters. In TT and TN–S
systems, where the N conductor is run separately from the PE conductor, the N conductor also has an arrester.
Valve-type arresters are constructed according to DIN VDE 0675 Parts 1 and 6 or IEC 99.1 and consist of a spark gap and voltage- dependent resistor connected in series; their nominal discharge surge current is 5 kA (8/20μs); the voltage arising at the consumer installation is about 1.5 kV.
Figures 5.8.1.3 a and b show valve-type arresters containing one air-
spark-gap and one silicon carbide resistor. Voltage and current charac- teristics for voltage limitation are shown in Figure 5.8.1.3 c. Valve-type arresters are characterized by their quenching voltage Ul (continuous
operating voltage Uc according to DIN VDE 0675 Part 6), at which an
arrester (in an operating duty test) is still able to extinguish the mains follow-current automatically. Figure 5.8.1.3 d shows the voltage and current during such an operating duty test according to DIN VDE 0675 Part 1 at a valve-type arrester for Ul = 280V, whereas Figure 5.8.1.3 e
shows the protection characteristic of this arrester.
If the valve-type arrester shown in Figure 5.8.1.3 a is overloaded, the integrated disconnector separates the defective arrester from the mains. Downstream consumer installations will stay alive. However, such defect- ive arresters must be replaced as they no longer protect against surges.
Figure 5.8.1.2 i DEHNgap B Figure 5.8.1.2 j Quench gap
Valve-type arresters have indicators to show the defective and discon- nected state (Figure 5.8.1.3 f).
Figure 5.8.1.3 g shows an arrester for NH fuse bases size 00 (connected
to L and PE). Figure 5.8.1.3 h shows a practical example. Replacement of an arrester in a live state is easy by means of an NH fuse handle. If holders with a microswitch (Figure 5.8.1.3 i) are used, the projecting pin of
Figure 5.8.1.3 b Nonlinear resistor type gapped surge arrester (acc. to Figure
5.8.1.3 a), installed in a low-voltage distribution system
Figure 5.8.1.3 a Nonlinear resistor type gapped surge arrester
Figure 5.8.1.3 c Performance of a nonlinear resistor type gapped surge arrester (series connection of spark gap and silicon carbide varistor)
Figure 5.8.1.3 d Performance of a nonlinear resistor type gapped surge arrester
(acc. to Figure 5.8.1.3 a) during the operating duty test
Figure 5.8.1.3 e Protective characteristic of a nonlinear resistor type gapped
surge arrester (acc. to Figure 8.1.3 a)
the disconnected arrester will press this switch and a remote indication of the necessary arrester replacement becomes possible.
Recent surge arrester models have zinc oxide varistors (Figure 5.8.1.3 j) where almost no mains follow-current arises; these can be used without a series connected spark gap. Figure 5.8.1.3 k shows such a surge arrester in a modular design with a thermally controlled zinc oxide varistor for space-saving installation in distribution systems (Figure 5.8.1.3 l).
The basic overvoltage limiting behaviour is shown in Figure 5.8.1.3 m;
Figure 5.8.1.3 h Surge arrester (acc. to Figure 5.8.1.3 g), installed in a
distribution system
Figure 5.8.1.3 f Nonlinear resistor type
gapped surge arrester with disconnector and indicator (acc. to Figure 8.1.3 a). Arrester on the right is defective, disconnector has operated (pushed up button)
Figure 5.8.1.3 g Surge arrester in
NH type of construction
Figure 5.8.1.3 k Surge arrester in modular design, type DEHNguard®
Figure 5.8.1.3 i Remote
indication of the operation of the arrester disconnector (acc. to Figure 5.8.1.3 g) by microswitch
Figure 5.8.1.3 j Metal oxide varistor
Figure 5.8.1.3 k Surge arrester in modular design, type DEHNguard®
the limiting voltage is exclusively determined by the residual voltage at the discharge of the impulse current. A live surge arrester on a metal oxide basis (without spark gaps) carries the current corresponding to its U/I characteristic (Figure 5.8.1.3 n). Such arresters are always ‘in operation’, whereas an arrester based on a spark gap needs ‘activation’ by an overvoltage.
Usual surge arresters based on ZnO have a discharge capability of
Figure 5.8.1.3 l Surge arrester DEHNguard® installed at the input of a power
supply line from lightning protection zone 1 to lightning protection zone 2
Figure 5.8.1.3 m Performance of a surge arrester based on metal oxide (acc. to
Figure 5.8.1.3 k)
15 kA (8/20μs). The protection element must be able to conduct this discharge current safely and without changing the characteristic at least 20 times. This is sufficient to prevent overloading in the case of a ‘creep under’ of a backup lightning current arrester and correctly dimen- sioned decoupling impedance (chapter 5.8.1.5). If for example, owing to unfavourable conditions, there is a missing backup lightning current arrester (in spark gap technology), this discharge capacity is exceeded and thus the varistor overloaded, then it will be automatically discon- nected from the mains. This prevents a defective arrester from disturbing the operation. Remote control is possible by a local indicator and a potential-free changeover contact.
DEHNguard® T (Figure 5.8.1.3 o) consists of two parts: a base and an
attachable varistor module which can be replaced in case of overloading. For insulation measurements of the system, quick removal is advanta- geous. To avoid errors, the base and varistor module are provided with code pins according to their nominal voltage.
Figure 5.8.3.1 p shows a surge arrester with degree of protection IP ×
4W. This is particularly suitable for industrial applications (to be plugged into NH fuse holders, size 00) and has (like the arrester shown in Figure 5.8.1.3 g) an integrated backup fuse which does not need any further backup fuse on the mains (section 5.8.1.5).
The 3+ 1 circuit (chapter 5.8.1.5) allows the application of surge arresters upstream of the residual current device. The three phase con- ductors (L1, L2, L3) are connected to varistors towards the neutral con-
ductor N, and the surge arrester DEHNgap C (Figure 5.8.1.3 q), based on a spark gap having a sparkover voltage of about 1.5 kV (1.2/50), is
Figure 5.8.1.3 n U/I characteristic of a varistor
installed between neutral conductor N and protective conductor PE. Thus, the upstream fuse can meet the disconnection requirements in the case of a fault.
The space-saving one modular design of the surge arresters DEHN- guard® and DEHNgap C and the multifunction terminals for wires and
usual comb-type bars make them especially easy to install.
5.8.1.4 Surge arresters for application at socket outlets, class D
Surge arresters for mobile application at socket outlets (overvoltage cat- egory II) are assigned to requirement class D according to E DIN VDE 0675 Part 6. Such pluggable protectors (Figure 5.8.1.4 a) are often equipped with additional filters (Figure 5.8.1.4 b). The SF protector has a visual function indicator (green lamp) and a visual fault indicator (red lamp). When overloading it is disconnected automatically from the mains without power interruption. The plug-in surge protection adapter shown in Figure 5.8.1.4 c is a combination of surge arrester and interfer- ence suppressor filter.
Further types of surge arresters used in this range are shown in Figures