Electricity + Control January 2018

EARTHING + LIGHTNING PROTECTION

abbreviations ELV – Extra Low Voltage GDT – Gas-discharge Tube IEC – International Electro- technical Committee LPS – Lightning Protection System MOV – Metal-oxide Varistors PE – Protective Earth SPD – Surge Protective Device

age of a GDT is increased – in comparison to the discharge of slow-rising voltage impulses.

fect solution for an efficient diversion and mitiga- tion of all kind of short-duration and long-duration surges. Testing of surge-protective devices In IEC 62305-3 [4] and IEC 62305-4 [1] it is stipu- lated that lightning protection systems shall get in- spected periodically. During a visual inspection it is not possible to assess the status of a SPD properly. A proper assessment is only possible by carrying out measurements in accordance with the man- ufacturer's instructions. To be able to test SPDs comfortably and in a safe way it is recommended to use pluggable SPDs. A high-voltage test device is needed for the proper testing of SPDs. References [1] IEC 62305-4. 2010. Protection against light- ning − Part 4: Electrical and electronic systems within structures. [2] IEC 61643-11. 2011. Low-voltage surge protec- tive devices − Part 11: Surge protective devic- es connected to low-voltage power distribution systems - Requirements and testing methods. [3] IEC 61643-12. 2008. Low-voltage surge protec- tive devices − Part 12: Surge protective devic- es connected to low-voltage power distribution systems - Selection and application principles. [4] IEC 62305-3. 2010. Protection against lightning − Part 3: Physical damage to structure and life hazard.

Suppressor diodes Suppressor diodes are less powerful, but very fast-acting voltage-limiting components. Their operation characteristic is comparable with the operation characteristic of varistors. The residual voltage of suppressor diodes is usually lower than the residual voltage of a varistor with the same dis- charge capacity. Suppressor diodes are less prone to ageing than varistors. Therefore a thermal moni- toring of suppressor diodes is usually not required. Because of the limited discharge capacity of sup- pressor diodes, they are mainly used in Class III SPDs for circuits with extra low voltage (ELV). SPDs with a series connection of a varistor and a GDT are frequently used for the protection of electrical systems where repetitive voltage spikes can be expected. During the conduction phase the residual voltage stays at a relatively high voltage level. SPDs with a series connection of a varistor and a GDT can sometimes be used as first stage of protection. Due to the high level of the residual voltage, their protection effect – during long-du- ration lightning impulses – is not as good as the protection effect of spark gaps with a low level of the residual voltage. To achieve an optimised protection effect, some- times different surge-protective components are connected directly in parallel. Triggered Class I spark gaps are the best choice to divert high-en- ergy long-duration lightning currents, and Class II varistors are the best choice to divert man-made short-duration switching overvoltages. A triggered Class I spark gap and a Class II varistor, connected in parallel right at the service entrance, are the per- Series connection of surge-protective components Parallel connection of surge-protective components

Figure 2: Fully automatic high- voltage test device for the safe electrical testing of pluggable SPDs.

Holger Heckler is in Product Marketing Surge Protection, Busi- ness Unit TRABTECH, at Phoenix Contact GmbH & Co. KG. Enquiries: Tony Raynor, Phoenix Contact South Africa. Tel: +27 (0) 11 801 8200 Email: tonyr@phoenixcontact.co.za or hheckler@phoenixcontact.com

26 Electricity + Control

JANUARY 2018