Measurements and modeling of EMC, applied to cabling and wiring

A myriad of cables transport power and communication signals in larger buildings and installations. Cross talk between cables and connected equipment is a major concern. Regulations do exist, but often show to be insufficient to avoid undesirable coupling. The current thesis research addresses this problem and provides a tested model for the interference coupling in buildings, in particular those caused by lightning. The model should also give an insight in the reliability of cabling and wiring, even when not all details of the installation are known. This was the goal as proposed in the IOP-EMVT project 'Optimal cabling in buildings and installations qua EMC'. A newly built pharmaceutical plant acted as main test object. In the measurements, currents of 0.3 kA were injected in the lightning protection grid on the roof. Inside the building, 100 m long test cables followed the path of other installation cables on the ladders and trays. The measured current and voltage are typical for the other cables. A simplified model of the installation included most designed current paths. It was implemented in method-of-moments program FEKO. Measurements and model agreed that the roof steel skeleton carried about 80 % of the current and the intended lightning conductors 20 %. A nearby, non-intended conductor (an air duct) had to be included in the model to obtain acceptable agreement between the calculated current through a cable support and the measured one. For three types of cables, the measured voltages agreed with the currents when combined with the transfer impedance measured in the laboratory. The agreement allows extrapolating the model to real lightning. This has been done in two steps, the first and simple takes the cable transfer impedances into account; the second and more complicated also includes travel time and resonances in the installation. The differences between both are limited for the Profibus fieldbus cable and not for the 2-lead cable with steel armor. The transfer impedance of the cables showed the advantages of armored cables even inside buildings. Additional interconnects to ground constructions cause a reduction of the lightning current inside a structure. They reduce the excitation of internal building resonances and shift the resonance frequencies upwards. Unrealistic artifacts in model results should be avoided by including a sufficient number of interconnects. Other shorter experiments are presented. For example: measurements and calculations on the lightning safety of an electronic lamp driver have been carried out on request of Philips Lighting. Based on the knowledge developed, an effective remedy against unacceptably large damage could be given. Simple configurations serve as direct test case for the models, such as the current distribution over a set of two 70 m long horizontal grounding electrodes. We compared measurements and the FEKO model, with simple analytical expressions. The interesting frequency range is up to 1 MHz, of relevance for lightning and conducted interference in switched mode power supplies

A case study on lightning protection, current injection measurements, and model

A newly built pharmaceutical plant has been investigated by measurements. Currents of 0.3 kA were injected in the lightning protection grid on the roof. Inside the building, test cables of 100 m length followed a path typical for cables belonging to the installation. We measured induced cable currents and voltages. A reduced model of the building incorporated most of the designed current paths. Measurements and model showed that the roof steel skeleton carried about 80% of the current and the intended lightning conductors 20%. The calculated current through a cable support was larger than measured. This is explained by also considering a nearby nonintended conductor. For three types of cables, we determined the transfer impedances. The measurements and model have been combined and extrapolated to actual lightning

Interconnections in buildings improve lightning protection

Two simplified models for a large building are compared for their lightning protection properties, one without and one with interconnecting conductive elements. The dimension is 69 × 19 m. At frequencies below 10MHz, the additional elements provide a skin-effect like protection of the building interior. The benefits of the interconnections at high frequencies are the suppression of resonances and shifting these to still higher frequencies where lightning is less prominent

Lightning protection of a pharmaceutical plant, measurements and modelling

The lightning protection of a pharmaceutical plant has been tested by current-injection on the structure. The study aims at two goals: 1) proof of safety by scaling the currents and voltage to lightning realistic values and 2) a comparison between measurements and a Method of Moments calculation. We measured the current distribution near the source and the induced currents and voltages in test cables. The cables and their 100 m long path were representative for the actual installation. By necessity the model is simplified, because of the large number of conductors, intended and unintended, and the uncertainty of their interconnection. The calculated currents are a factor of 3 larger than measured. © 2009 IEEE

Lightning protection improved by multiple interconnects in buildings

Two simplified models for a large building are compared for their lightning protection properties, one without and one with interconnecting conductive elements. The dimension is 69 × 19 m. At frequencies below 2 MHz, the additional elements provide a skin-effect like protection of the building interior. The benefits of the interconnections at high frequencies are the suppression of resonances and shifting these to still higher frequencies where lightning is less prominent

A case study on lightning protection, building resonances considered

In a recent paper (G. Bargboer and A. P. J. van Deursen, IEEE Trans. Electromagn. Compat., vol. 52, no. 3, pp. 684-90, Aug. 2010) we dealt with current injection measurements to test the lightning protection system of a newly built pharmaceutical plant. In a tentative extrapolation, the measurements were extrapolated to actual lightning. Here, we extend the model and calculate the response of the installation on lightning currents and include resonances in the cable trays and test cables contained in it. It turned out that suspension rods between roof support and cable tray were indispensable to suppress the resonances. The time dependence of the present results and the earlier simplified model given in differ greatly, but the amplitudes of induced voltages appear to be of the same order of magnitude

Lightning test on an electronic lamp driver

Two electronic drivers for gas-discharge lamps have been tested for the immunity of lightning induced common mode currents. A series of tests with increasing threat level have been applied, given equipment available in the TU/e high-voltage laboratory. One type of unit turned out to be damaged by CM currents of the order of 100 A. This unit proved also quite sensitive to lightning in practice. The other unit remains functional with 2.5 kA

Finding weak spots in lightning protection

The lightning protection of various industrial installations has been investigated by injecting current of smaller amplitudes. Large deviations of the intended current distribution and high values of induced voltages have been observed. Local measures can remedy the deficiencies