IEC 61000-2-10-2021 Electromagnetic compatibility (EMC) – Part 2-10: Environment – Description of HEMP environment – Conducted disturbance.
5 Description of HEMP environment, conducted parameters
5.1 Introductory remarks The electromagnetic field generated by a high-altitude nuclear explosion described in IEC 61 000-2-9 can induce currents and voltages in all metallic structures. These currents and voltages propagating in conductors represent the conducted environment. This means that the conducted environment is a secondary phenomenon, a consequence of the radiated field alone. All metallic structures (i.e., wires, conductors, pipes, ducts, etc.) will be affected by the HEMP. The conducted environment is important because it can direct the HEMP energy to sensitive electronics through signal, power, and grounding connections. It should be noted that there are two distinct categories of conductors: external and internal conductors (with regard to a building or any other enclosure). While this can seem simplistic, this separation is critical in terms of the information to be provided in this document. The difference between these two types of conductors is explained by electromagnetic topology. In general, external conductors are those which are located outside of a building and are completely exposed to the full HEMP environment. This category includes power, metallic communication lines, antenna cables, and water and gas pipes (if metallic). For the purposes of this document, the conductors can be elevated above the ground or buried in the earth. Internal conductors are those which are located in a partially or completely shielded building where the HEMP fields have been reduced by the building. This is a much more complex situation, because the HEMP field waveforms will be significantly altered by the building shield, and the coupling to internal wires and cables is consequently very difficult to calculate, although some measured data are available from simulated HEMP tests. In this document the external conducted common mode environments are calculated using simplified conductor geometries and the specified HEMP environments for the early, intermediate, and late-time waveforms. These conducted external environments are intended to be used to evaluate the performance of protection devices outside of a building, and because of variations in telecom and power systems, the effects of transformers and telephone splice boxes are not considered here. This process results in approximate, but well-defined waveforms that are needed to test protective elements on external conductors in a standardized manner. For the internal conductors, a procedure is defined to estimate the conducted environments appropriate for equipment testing. For unshielded multiconductor wires, it is assumed that the line-to-ground currents are equal to the common-mode current.
5.2 Early-time HEMP external conducted environment For the early-time HEMP, the high-amplitude electric field couples efficiently to antennas and to any exposed lines such as power and telephone lines. The antenna coupling mechanism is extremely variable and dependent on the details of the antenna design. In many cases, it is advisable to perform continuous wave (CW) testing of an antenna and to “combine” the response function of the antenna with the incident HEMP environment using a convolution technique. However, simple formulae have been provided to compute the response of thin antennas (see 5.5). For long lines, it is possible to perform a comprehensive set of common mode calculations that are reliable and depend only upon a few parameters. These parameters include conductor length, exposure situation (above ground or buried), and the surface ground conductivity (for depths between 0 m and 5 m). In addition, because the HEMP coupling is dependent on angle of elevation and polarization (see Figure 1 ), it is possible to statistically examine the probability of producing particular levels of current.IEC 61000-2-10 pdf download.