Protection increases system availability
October 2009, Electrical Power & Protection
Information supplied by DEHN + SÖHNE, Germany
Modern technology combined with suitable maintenance strategies increase system availability and are thus important factors for higher economic efficiency. Regular maintenance and repair work to increase the system availability is a top priority in the field of lightning and surge protection. Nevertheless, maintenance and repair expenses should also be kept to a minimum through the implementation of an appropriate strategy.
Just as with other electrical and electronic devices, electronic components in surge protective devices (SPDs) are subject to ageing. This is illustrated in the ‘tub-curve’ of Figure 1.  Figure 1
The reason for a maintenance strategy for SPDs is to identify the fault before the SPD fails. For this purpose, DEHN + SÖHNE developed an efficient maintenance strategy based on required system availability.
Damage-oriented maintenance
In this case maintenance measures will only be taken after the protective devices have failed. Three protective device features are important for applying this maintenance strategy, these are:
* Fail-safe – in the case of an overload the arrester will short-circuit the signal line. (Although the information signal is interrupted the system is still protected against surges.)
* Use of pluggable arresters consisting of a base part and protection module. (Pluggable arresters consist of a protection module for the discharge processes and a base part establishing the contact between the protection module and data lines.)
* Make-before-break switch contacts in the base part. (If there is no protection module installed the switch contacts in the base connect the input side of the data line to the output side. Thus data transmission is possible even without a protection module being plugged-in.)
What happens if an SPD reaches the end of its service life or is damaged without fail-safe characteristics? The arrester unnoticeably loses its surge protective function leaving the system to be protected vulnerable to damage by surges. This fault will not be noticed until the surge protective device is inspected or the faulty arrester starts causing interference with the signal transmission of the system. To rectify this failure, the faulty arrester has to be removed and a new one installed. It is important that a suitably qualified person performs the fault analysis and repair.
Fail-safe performance of a faulty arrester prevents surge damage to the system; data transmission can be restored by simply removing the faulty module. (Without protection modules, the base part serves as a maintenance-free feed-through terminal.) In order to restore normal operation with active protection a new protection module has to be plugged into the base part, this is quick and easily achieved.
BLITZDUCTOR XT (BXT) interrupts the signal flow in case of failure. It consists of a base part and a protection module and is equipped with a make-before-break switch contact in the base part as shown in Figure 2. Reliable protection, easy maintenance and thus increased system availability are assured.
Maintenance tests and intervals for lightning protection systems are specified in the DIN EN 62305-3 standard, supplement 3. This is not so easy where SPDs are installed in information systems as their state is not always visible.  Figure 2
Preventive maintenance with LifeCheck
The LifeCheck monitoring device detects thermal and electrical overload of all components. In order to prevent imminent failure and thus system downtime the suspect protection module should be replaced as soon as possible.
This type of SPD testing provides the following benefits:
* Easy to implement with fast results.
* Detection of thermal or electrical overload on all components.
* In order to increase system availability, test intervals can be shortened without significantly increasing maintenance effort.
Condition monitoring (Figure 3)  Figure 3
In some industries maximum system availability has to be ensured, condition monitoring based on LifeCheck technology is a feasible solution. For this purpose, an RFID reader integrated in the switchgear cabinet is used providing the following benefits:
* Permanent SPD monitoring during operation.
* Remote signalling option via RS485 and remote signalling contacts.
* Gateway for connection to a control system or other system bus.
* Condition Monitoring – PC software included.
DEHN + SÖHNE offers surge protective devices which reliably protect system installations and are suitable for all maintenance strategies (Figure 4).  Figure 4 For more information contact Paul van As, Surgetek, +27 (0)11 792 1303, info@surgetek.co.za, www.surgetek.co.za
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