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14  March  2012

  Stuart Jaycocks, Strategic Marketing Manager, Weidmüller Limited, takes a look at Standard BS EN 62305

Electronic systems now encompass almost every aspect of our lives. The use of computers, electronic process controls and telecommunications has increased dramatically over the last two decades. Not only are there more systems in existence, but the physical size of the electronics involved has reduced considerably – which means that their circuitry can be easily damaged by lower levels of energy and power surges.

The most familiar source of a power surge is lightning, though it is in fact one of the least common causes. A more common cause of power surges is during the operation of high-power electrical devices, such as elevators, air conditioners and refrigerators. These high-powered pieces of equipment require a lot of energy to switch on and turn off components. This switching creates sudden, brief demands for power, which can disrupt the steady voltage flow in the electrical system. While these surges are nowhere near the intensity of a lightning surge, they can be severe enough to damage components.

Other sources of power surges include faulty wiring, problems with a utility company's equipment, and downed power lines. The system of transformers and lines that brings electricity from a power generator to the outlets in our homes or offices is extremely complex. There are dozens of possible points of failure, and many possible errors that can cause an uneven power flow.

The BS EN 62305 standard was introduced with a vast amount of detail on how to choose the correct surge protection device for your applications. Because risk assessment is now a far more comprehensive and laborious task, the volume of the documentation grew massively from that which accompanied the previous BS 6651 standard.

BS6651 only dealt with the protection of the physical structure and was written in 1985 by a UK technical committee. By comparison, BS EN 6230, written by the IEC – International Electrotechnical Commission based in Geneva, includes risk management, including the risk of loss of human life, loss of service to the public, loss of cultural heritage and economic loss. It is the result of many years of successful collaboration by hundreds of lightning protection experts from 28 different countries. It is a difficult and most expansive document, yet crucial for our industry.
The biggest challenge operatives face today is the practical application of the lightning risk assessment. The reason for this is that it requires considerable additional information to ensure the whole building is adequately protected. This includes not only the structure but also the services, telecommunications and the power lines which supply it. Given our reliance on digital services today – this is no small task.
Risk assessors need to consider factors such as the overall dimensions of the building structure, its uses and the type of equipment installed both inside and out. Understanding the composition of floor surfaces and the location of power and telecoms cables - and their proximity to other structures - are also key considerations, as is, of course, fire protection.
It is reported that around one million flashes strike the ground every decade in the UK. Yet, despite these apparent dangers and the critical nature – and vulnerability - of many business systems, the continued high numbers of insurance claims for lightning damage suggests that many organisations are still not taking adequate lightning protection measures.

In today's system of electricity distribution, power surges are an unavoidable occurrence. Power surges can occur when something boosts the electrical charge at some point in the power lines. This then causes an increase in the electrical potential energy, which in turn can increase the current. A number of different things can cause this to happen. When lightning strikes near a power line, whether it's underground, in a building or running along poles, the resulting electrical energy is boosted by millions of volts.

Lightning bolts and other voltage peaks require increased protection of equipment. Especially at risk are free-standing areas of power plants far away from the main building, e.g. control units of a fuel storage, of water processing or telecontrol installations. Furthermore, solar and wind power plants also require special attention regarding surge protection. A surge protector (or surge suppressor) is an appliance designed to protect electrical devices from voltage spikes. A surge protector attempts to regulate the voltage supplied to an electric device by either blocking or by shorting to ground voltages above a safe threshold.

If the surge or spike is high enough, it can cause some serious damage to a machine. When too much electrical pressure runs through a wire -- the wire can burst and burn. Even if increased voltage doesn't immediately break the machine, it may put extra strain on the components, wearing them down over time. Surge protectors can assist in preventing this from happening.

A standard surge protector passes the electrical current along from the outlet to a number of electrical and electronic devices plugged into the power strip. If the voltage from the outlet surges or spikes, the surge protector diverts the extra electricity into the outlet's grounding wire. In the most common type of surge protector, a component called a metal oxide varistor, or MOV, diverts the extra voltage. An MOV forms a connection between the hot power line and the grounding line. An MOV has three parts: a piece of metal oxide material in the middle, joined to the power and grounding line by two semiconductors.

If voltage in the circuit is too high, an MOV can conduct a lot of current to eliminate the extra voltage. As soon as the extra current is diverted into the MOV and to ground, the voltage in the hot line returns to a normal level, so the MOV's resistance shoots up again. In this way, the MOV only diverts the surge current, while allowing the standard current to continue powering the machines that are connected to the surge protector.

BS EN 62305 Protection against Lightning comprises four parts. Part 1, General Principles, introduces you to the other parts; Part 2 is Risk Management, which defines the level of Lightning Protection System required, based on a risk assessment; Part 3 relates to physical damage to structures and life hazards; and Part 4 covers the protection of electrical and electronic systems within structures.

A business should begin by assessing how much it is at risk by the types of loss that it could incur, should it be struck by lightning or a power surge. There are four types of loss defined in BS EN 62305: loss of human life, loss of service to the public, loss of cultural heritage (ie: historic buildings or monuments) and loss of economic value. This last type considers the cost of the physical loss of the equipment, but not the consequential losses as a result of downtime. In making this assessment, it is important to remember that there are two types of lightning strikes – direct and remote strikes.

Direct or close strikes are those into the lightning protection system of a building, in close proximity to it, or into the electrically conductive systems implemented in the building, such as the low-voltage supply, telecommunications or control lines. Remote lightning strikes are those that occur at a distance as well as lightning strikes into the medium voltage overhead system or in close proximity to it, or lightning discharge from cloud to cloud.

Once the risk is assessed, you will then need to look up in the table in the National Annexes, the tolerable risk for these types of losses. By using a series of calculations within the standard you will be also be able to calculate the actual risk. Logically, if the actual risk is higher than the tolerable risk, then the protection requirements are set out in the tables in the standard.

Part 3 of the Standard defines four levels of lightning protection based on possible minimum and maximum lightning currents, which relate to classes of lightning protection systems. These are used to define several attributes of the lightning protection systems. The standard also recommends a single integrated termination system for a structure and provides detailed explanations on the reasons for equipotential bonding. It explains the choice of lightning protection system components and conductors with various tables relating to sizes and types of conductor and earth electrodes.

The final part of the Standard, Part 4, has arisen as a result of the increasing cost of failures of electrical and electronic systems, caused by electromagnetic effects of lightning. It provides information on protection measures to reduce the risk of permanent failures of electrical and electronic systems within structures. Part 4 also covers the design, installation, inspection, maintenance and testing of a lightning electromagnetic impulse protection system for electrical and electronic systems within a structure. And finally, there’s guidance on how to reduce the risk of permanent failures due to lightning electromagnetic impulse.

The scope and diversity of surge protection devices can be as complex as the new Standard, from lightning arresters, high power varistors and surge monitoring modules, to data interfaces and surge protection for photovoltaic systems. With this clear definition from BS EN 62305, you no longer need to be at risk.

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