This application note discusses the nature of the threat to electronic instrumentation and communications networks posed by voltage surges induced by lightning or other causes.
The practical application of surge protection devices (SPDs) designed to prevent damage from such sources is described. It is the intention to discuss suitable techniques to protect electronic circuits and equipment from high voltages and surge currents induced by lightning and other forms of transients.
The need for surge protection
Most process control or telemetry installations are interconnected by power and signal cables which run on trays, in ducting or via overhead poles. Lightning strikes, static discharges and induction from power cabling are typical sources of transient voltages which can be coupled into signal cables and hence transmitted to electronic equipment. Field transmitters, computer terminals, etc, containing low-power semiconductor devices can be damaged by over voltages of only tens of volts. The longer the cables, the more frequent the occurrence of high voltage transients through shifts in ground potential, so devices controlling or monitoring events in remote locations are more likely to suffer from over voltages and consequent component failures. Significant damage can also be found in equipment connected by relatively short cables if the circuits or components are particularly sensitive – as is the case for computer data communication ports.
As an illustration, consider the effects of a lightning strike to a building housing control and telemetry equipment, of which the fabric is protected from a direct strike by lightning conductors and ground rods. The conductor carries the very large strike current to ground where the charge transfer is dissipated into the mass of the earth.
The effect of this current is to elevate the reference potential at the building. For example, if the strike current is 100 kA and the conductor/ground impedance is 10 Ω, then the potential above ground is 1 million volts. Exposed metalwork within the building is bonded to the same reference potential and so only small voltage differences exist that pose little risk to personnel.
However, consider a field transmitter pole-mounted away from the control building but connected to the telemetry electronics by signal cabling. Most transmitters incorporate some level of isolation from structural earth, typically 500 V. This level of isolation now has to withstand the transient voltage between the new building reference potential and its local earth potential. Many transmitters can be destroyed in this way, even though the actual lightning strike was to a protected building.
Readers wishing to find out more about surge protection devices and strategies can view the full application note at: http://instrumentation.co.za/+C13509
Power supply with scalability optimised Schneider Electric South Africa
Electrical Power & Protection
Schneider Electric has introduced the Easy UPS 3-Phase Modular to the South African marketplace. This robust uninterruptible power supply (UPS) is designed to protect critical loads while offering third-party verified Live Swap functionality.
Read more...Prioritising arc flash safety Comtest
Electrical Power & Protection
Comtest has developed a range of thermal imaging and wireless testing tools from Fluke, designed to ensure safety is the top priority for engineers working in potentially dangerous arc flash zones.
Read more...Monitoring the voltage drop in cables Turck Banner Southern Africa
Electrical Power & Protection
With its new M12Plus connectors, Turck Banner is directly shifting the condition monitoring of cables subject to severe stress to the connection technology. The connectors, which come with voltage and current monitoring and a Bluetooth chip, enable measured voltage and current values to be sent wirelessly to a controller.
Read more...Mesh networks: a multidirectional electrical superhighway Schneider Electric South Africa
Electrical Power & Protection
Today, many power industry stakeholders are faced with mounting requirements for improved grid reliability, resilience and distribution efficiency. It’s a challenge which requires power service providers to rethink their infrastructure. Enter mesh networks, which can overcome the limitations of traditional star networks.
Read more...Versatile flexible copper busbar
Electrical Power & Protection
Referro Systems specialises in the supply and support of industrial electrical, automation and global software and hardware brands, and is now able to offer the Cubic range of Cu-Flex flexible copper busbars.
Read more...Trafo Power Solutions upgrades DRC mine transformers
Electrical Power & Protection
With its experience in Africa and its agility in executing projects rapidly, Trafo Power Solutions is supplying three mini-substations and two transformers to a copper-zinc mine in the Democratic Republic of Congo.
Read more...Acquiring locally-manufactured transformers ACTOM Electrical Machines
Electrical Power & Protection
Speed and efficiency are of the essence in the fast-evolving power generation and distribution space; but a significant challenge is the prolonged lead times associated with acquiring transformers – key components in any electrical infrastructure.
Read more...Seaward testers power PV specialists Comtest
Electrical Power & Protection
One of Asia’s leading clean energy specialists, Solarvest, uses the latest electrical safety test equipment to ensure the solar photovoltaic (PV) installations it services and maintains operate at peak performance levels.
Read more...Multi-purpose contact block
Electrical Power & Protection
The TME catalogue has been expanded to include products from Schlegel. This German, family-owned company has been specialising in the production of high-quality electromechanical components for almost 80 years.
Read more...ACTOM supplies transformer units to Kamoa Copper Mine ACTOM Electrical Machines
Electrical Power & Protection
ACTOM Distribution Transformers, recently secured an order for the supply of its neutral electromagnetic couplers, with earthing resistors, and an auxiliary transformer) to Kamoa Copper Mine in the DRC.
printer friendly version