Electricity + Control August 2015

ELECTRICAL PROTECTION + SAFETY

Periodic inspection of portable earthing and short-circuiting devices Reduced cable cross-sections of portable earthing and short-cir- cuiting devices (EaS devices) resulting from copper corrosion and breakage of conductor strands, or increased resistances in the con- nections, may have fatal consequences when earthing and short- circuiting devices are subjected to short-circuit currents.Therefore, portable EaS devices must be tested prior to each use and at reg-

ular intervals. So far, only a visual inspec- tion made eco- nomic sense. A newprocedure is now availa- ble which pro- vides reliable information on the condition of the portable

EaS device based on static and dynamic measurements of the ohmic resistance. DEHN AFRICA offers this improved test for portable EaS devices on the customers’ premises. An earthing and short-circuiting device is tested in three steps and the resistance values are compared with theoretically and experimentally deter- mined limit values.The first step is the visual inspection for visible signs of damage. A static test is performed in the second step, in which the absolute resistance value is measured at the station- ary earthing and short-circuiting device. Step three includes the dynamic test, which notes the measurement of the relative change in resistance at the moving earthing and short-circuiting device. The measurement of the resistance change value ΔR between the non-moving and the moving EaS device is a new approach which allows for the detection of local damage, such as breakage of conductor strands in the conductor cable. To prove the effectiveness of protection measures, it is often nec- essary to perform lightning current tests on complete systems. DEHN ’s newly designed test laboratory generates extremely high lightning currents with a peak value up to 400 kA in the standard- ised 10/350 μs test wave form. This powerful test laboratory allows for the testing of light- ning protection systems for installations and systems requiring maximum protection.The performance of the test laboratory has been doubled so that lightning impulse currents twice as high as that required for the maximum lightning protection level (LPL I: 200 kA (10/350 μs)) described in the latest IEC 62305-1 lightning protection standard, can now be simulated. The test centre consists of five different laboratories, extend- ing over a floor space of 800 m 2 . It is equipped with the latest devices and technologies essential for developing new products and practical solutions. Enquiries: Alexis Barwise. DEHN Africa.Tel. 011 704 1487 or email alexis.barwise@dehn-africa.com Enquiries: Alexis Barwise.Tel. 011 704 1487 or email alexis.barwise@dehn-africa.com Launch of lightning impulse current laboratory

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