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Perimeter security in high EMF environments

Electromagnetic Field (EMF) interference at power stations poses a formidable task for many perimeter detection systems due to the extremely high EMF produced by extra high tension (EHT) overhead cables from these plants which connect to the national grid. Electromagnetic Induction (EMI) is the production of voltage or an electromotive force due to a changing magnetic field, this is produced by EHT lines feeding to or from generation or distribution points on the national grid.

EHT Lines over fence.

When electrical or electronic equipment operates in an extreme EMF environment, the effect of the induction can play havoc with the proper function of security equipment. The effect can be exacerbated where long lengths of cable are connected to electronic equipment. However, if due care is taken with the installation, systems can work as intended, operating normally.

For this to happen the installation needs to be properly earthed and effectively (electrically) screened from this EMF. Equally important for proper system functionality is the design of the equipment and its ability to withstand certain levels of environmental EMI and then also, by filtering, to inhibit or attenuate EMI in the frequency bands they occur and the harmonics of these bands.

Proper earthing points need to be in place and, in most cases, especially designed earth mats at these types of generating plants or power distribution hubs exist. So, the proper earthing and bonding of the perimeter fence is critical for the reduction of EMI on the AcoustAlert sensor cables which are fixed to the perimeter fence. The AcoustAlert field processor also employs filtering of unwanted EMI and their harmonics. The result is AcoustAlert works as intended on the perimeter security fence of power generation plants or distribution yards.

AcoustAlert was installed at such a plant in Port Elizabeth 10 months ago and operates normally with no false alarms as a result of possible EMI interference. In addition, it has operated without fault over this period.

AcoustAlert perimeter intrusion detection forms part of our layered approach to security solutions for key point installations.

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