When we hear the term “surge”, we immediately think of lightning strikes. This is certainly the most spectacular case of voltage spikes, but it is not the most common one, as well as not the most harmful one. Strikes in the vicinity of an object (the influence of indirect strikes is sensed on installations up to 1.5 km away from the point of a lightning strike) and the influence of the electrical grid (inductions. the switching control of bigger loads, temporary overvoltages) can be often more harmful. These kinds of voltage spikes are manifested in several ways, among which the following are the most common: faster ageing of components, equipment resets, equipment shutdowns, and even its failure in the most severe cases.

Even though a lot of attention has been directed to the surge protection of data centres, there have been several shutdowns or failures of systems in 2011 due to voltage spikes. The most significant one was probably the shutdown of the Amazon computer centre in Ireland in August, since the system is the second largest in Europe and the fifth largest in the world. Although the information on causes differs slightly, most reporters state that the shutdown was a consequence of a lightning strike into the transformer that powers the aforementioned data centre. Simultaneously, also the system responsible for switching to emergency generators failed. The recovery from the aftermath and the creation of copies of the majority of documents took a day or two. In the meantime, some companies were not able to access their data, and the confidence into the cloud services was severely damaged. There is no exact information on the damage caused by the failure, but it is certainly very extensive, since Amazon is offering their users to pay an indemnity for the losses, and free usage of their services for one month as compensation.

In order to prevent the occurrence of similar events, data centres have to be appropriately protected; but to provide a suitable protection, some conditions have to be met. Although some believe that the installation of a lightning protection system alone is sufficient to protect a building, that is not the case. Various research and measurements have shown that the effects of voltage spikes are distributed through all connections leading into a building. All those connections act as antennas “channelling” different influences from the environment. Each building therefore needs:

1. lightning protection

2. grounding systems

3. potential equalization

4. low voltage power supply (230V AC/400V AC) surge protection

5. data surge protection

If all the aforementioned points are optimally taken into consideration, also the cost structure distribution allow for the largest portion of assets to be used on lightning protection and proper grounding, as well as potential equalization, whereas the smallest portion is used for surge protection. If there is no lightning protection or the grounding is unsuitable, or there is no equipotential equalization, the cost structure is reversed. In this case, the surge protection can represent the highest cost of the protection against the influence of lightning and other voltage spikes.

It is therefore of the utmost importance to dedicate proper attention to every field of protection. Improper grounding can directly affect the quality of surge protection. Absence of a lightning rod, or if it is unsuitable, can have a similar effect on electrical installations as well.

A suitable protection for the building is the lightning protection executed in accordance with the applicable standards. The execution of the lightning protection itself depends mostly on the form of the building. There are different methods of a lightning protection planning. The EN 62305-1 to -4 norm defines three methods: the rolling sphere method, the mesh method, and the protective angle method. By means of standard methods, the protection level is determined.

Of course, a lightning protection itself does not provide a suitable protection if it is not properly grounded. According to the regulations, the resistance of the grounding application shall not exceed 10 Ω. We are often not aware of the importance of ground resistance until lightning strikes. Since the amperage of a direct lightning strike can exceed 100 kA, electric discharges between lightning protection systems and other electrical installations can occur in case of improper grounding. The operation of surge protection applications is also limited in case of unsuitable grounding since it does not function properly.

In order to prevent discharges between various metallic conducting elements, potential equalization is necessary. The equalization can be executed by short-circuiting both metallic parts, or by inserting an element for equipotential equalization between them. Direct equalization is used for systems that have to be grounded, while elements for the separation of equipotential surfaces are used in systems that may not be in direct contact. The separation of equipotential surfaces is executed by means of a special surge arrester variant. In the normal mode of operation, the surge arrester is in the high ohmic range, thus representing the galvanic separation between both grounding applications. When a voltage spike occurs, the surge arrester switches into the low ohmic range and limits the voltage between both grounding applications, whose potentials are equalized in that way.

As already mentioned, quality grounding is of utmost importance both in case of lightning protection and surge protection. As a matter of fact, surge protection is just another element for potential equalization or limitation. Just like the grounding of a water supply system (where pipes are still made of conducting materials), gas supply system, and heating system is important, also the potentials of a low voltage installation, as well as of data transmission connections against grounding have to be determined.

Figure 1: External lightning protection system

Surge protection is an element that minimizes voltage spikes occurring on conductors, and reduces them to acceptable levels. This prevents voltages within the system that could damage connected devices. Voltage spikes that do occur are significantly higher than the protection levels of the devices themselves. This way, the operation of a fuse itself can cause damage on sensitive devices.

Surge protection functions very similarly to the elements for equipotential equalization. Of course, surge protection has to be chosen carefully. One of the main principles for choosing the right surge protection system is the protection zone concept described in the EN 62305-1 to -4 norms. Protection zones are divided into four basic zones, which are shown in Figure 2.

Figure 2

In the transition areas between protection zones, suitable surge protection applications have to be provided. In accordance with IEC 61643-1, they are divided into following groups:

-          Class I surge protection devices: These are current arresters for the protection of electrical installations and devices from direct lightning strikes.

Class I surge protection devices are placed in the main distribution box.

In the example in Figure 3, PROTEC B2S(R) 50 (3+1) surge arresters for the protection of lines leading from the transformer, the external air conditioning unit, and the emergency generator were used.

-          Class II surge protection devices: These are surge arresters for the protection of electrical installations and devices from indirect influences of lightning strikes, as well as from switching (industrial) surges.

Class II surge protection devices are placed in a sub-distribution box.

In the example in Figure 3, SAFETEC C(R) 160 (3+1) surge arresters were used. They were installed in the sub-distribution boxes of the data centre, of the control system, and the internal air conditioning unit.

-          Class III surge protection devices: These are surge arresters, dedicated exclusively to the reduction of harmful voltage spikes to the voltage threshold that electronic devices can still cope with.

Class III surge protection devices are placed as close to the protected device as possible.

In our case, the PROFILT D 8A protection system with an additional EMI filter was used, which additionally reduces the influence of high-frequency interference and voltage spikes. It was installed into the power supply part of the video control system, which is also an important component of the data centre as a whole.

Figure 3

However, protecting power connections alone is not sufficient. Also the appurtenant data transmission connections have to be protected. Although the main data transmission connections of the data centre are usually executed with optical fibres, there are also other data transmission connections within a data centre. These are very often connections, dedicated to the video surveillance, as well as connections for the access control system. If the access control system connections are short in some instances and run within the protection zone, due to which no surge protection is necessary, the video surveillance system connections are often highly exposed to voltage spikes. The figure below shows, how a video surveillance system is protected. In the represented case, type LZ-NET6 protection devices were used for the protection of IP cameras, as well as cameras compatible with the PoE standard.

Figure 4

Conclusion

In order to increase the efficiency and reliability of a data centre, it has to be suitably protected. An economical protection has to encompass lightning protection with necessary grounding applications, as well as low voltage surge protection, and data surge protection. If the lightning protection and the grounding are executed optimally, the surge protection costs will be kept low. In the opposite case, the protection has to compensate for all deficiencies, and its price can thus exceed the price of a lightning protection system.

Nevertheless, we have to be aware that only a suitably chosen surge protection can be efficient.

Prepared by: Aleš Golob