TechArchive

Original article date: March 1998

It is impossible to be successful in today’s world without electronic equipment yet we do little to protect it says MARK FREEMAN surge protection manager of OBO Bettermann

Have you ever stopped to imagine what it would be like to work today without electronic equipment? What jobs do you do during the day that don’t involve some kind of electronics ? CAD/CAM systems data processing personal computers instrumentation and control systems are all indispensable parts of our life.

Highly integrated electronic circuits are the core of such systems – “chips” incorporating tens of thousands of vulnerable functional units on a few square millimetres. Even small over-voltages of a few volts may result in the destruction of these sensitive components – and in the complete blackout of a system yet we do little to protect them.

Installation of an uninterruptible power supply (UPS) provides a lifeline offering a limited supply during times of a power loss provided there is no damage to the UPS itself. But even the best UPS can be susceptible to the larger surges and spikes. The failure of an electrical system by a computer crash destruction of hardware and software paralyses a business within seconds. Two to three hours of downtime can typically cost thousands of pounds an hour. System failings often mean fatal losses for companies yet we do little to protect against them.

In the US up to 40 million lightning strikes hit the ground each year. In the UK things aren’t so bad but with a one in ten chance of a lightning strike hitting the ground with every thunderstorm there is still a great need for over-voltage/surge protection. It only takes one strike within two miles of a building which has a low voltage supply or data/telecom line attached – and which buildings don’t – for sensitive electronic equipment within that building to be at risk yet we still do little to protect it.

Over-voltages don’t just come from lightning. They can also be generated by the collapse of inductive loads power service interruptions improper grounding component failure switching loads on and off and even human error.

Whether you are looking at protecting a fully automated manufacturing plant or just a domestic household OBO has developed a full range of devices which can be simply installed to protect both the mains and data lines comprehensively. Consider the cost of the electrical appliances in most households today: the washing machine tumble dryer TVs video microwave hi-fi personal computer. The cost of protecting all of these products together is less than the cost of any one item. In general the insurance companies can no longer manage without a supplementary policy for damage and you are advised to read the small print on your policy.

OBO Betterman’s over-voltage protection products range from DIN-rail mounted mains basic protection to mains fine protection from data line or process measuring and control protection to isolating spark gaps. Surge protective devices (SPDs or arrestors are pieces of equipment which are designed to protect other electrical equipment from inadmissible over-voltages. They mainly consist of voltage-dependent and/or series gaps. The elements may be connected in series or in parallel or can be used individually.

The basic protection can be mounted on standard 35mm DIN-rail and are supplied already connected with a built-in earth jumper bar reducing the earth connection to one connection point on site. The V-20-C/4 offers protection against maximum current surges of up to 100kA higher than many products on the market. The units are pluggable therefore individual pole arrestors can be replaced instead of the complete unit even with the supply still connected. The units are available with remote signalling. audible signalling and voltage monitoring built in and can be supplied complete with enclosures.

In the case of direct strikes into a lightning protection system the direct lightning current is discharged to the earthing system via the existing down conductors. The electromagnetic fields generated here are another threat to the electronic equipment within a building. To minimise these potential dangers lightning protection zones are graded.

Zones are established by a complete building or room screening. The screens can be formed from existing metal fronts. The lines passing a lightning protection zone must be equipped with the appropriate protection devices at the zone interface. These devices are then connected to the local equipotential bonding.

Lightning protection zones are defined according to IEC 1312-1 and VDE 0185 part 103.

Lightning protection zone 0A

Direct lightning may occur here. The electromagnetic field is effective without limit.

Lightning protection zone 0B

This is the area that is protected from direct strikes. The electromagnetic field is effective without limit.

Lightning protection zone 1

In this zone only partial lightning currents can flow though – eg arrestors or equipotential bonding lines. The electromagnetic field is dampened by screen 1

Lightning protection zone 2

The lightning partial currents occurring here are reduced by the lightning protection zone 1. The electromagnetic field is further dampened by screen 2.

Lightning protection zone 3

Further reduction of the lightning partial current and the electromagnetic fields.

Where do Overvoltages originate ?

The four sources of overvoltages are;

The direct strike.If lightning immediately strikes the building the housings and protective conductors of all electrical installations connected to the foundation earth are brought up to a high potential within a few microseconds. A large equalising current flows from the earth parts of the devices to the feeding system of the data or low voltage network. At the same time high voltages may be induced in conductor loops which are connected to the equipotential bonding.

Remote strike into the low-voltage network.Even if the building itself is not involved the effect of the lightning strike with its travelling waves and the high voltage amplitudes that are propagated with almost the speed of light along the feeding line will endanger each electronic system. The consequences before the thunder can be heard computers control systems TVs and most electronic equipment can be destroyed.

Travelling waves on the mains and data lines.Whoever is pleased when the lightning does not strike the earth but travels from cloud to cloud rejoices too soon. Cloud to cloud lightning strikes release mirror charges and generate as fast as lightning travelling waves on mains and data lines with the same result as described earlier.

Switching operations in the low voltage network.If an electronic system quickly fails without the presence of lightning the effects are the same only the cause is different. Switch-on and switch-off operations involving capacitive and/or inductive loads and even ground faults or short circuits in the energy supply network may generate large magnitude voltage spikes.

• OBO Bettermann
• 01933 442800

March 1998