Re: [HCDX]: Re: Noise from power lines

["Fernando de Sousa Ribeiro" <fernando-m-ribeiro@xxxxxxxxxx>]

The noise generated by power lines is a matter of great concern to
electricity suppliers. The main reason for this is power electronics.
Whatever function it performs (in rectifiers, inverters, motor
controllers, etc.), it usually involves the repeated switching of
large currents, which can be as high as thousands of amperes, as it
happens in some industrial plants. This switching action generates
harmonic frequencies that are radiated, as well as conducted along the
lines, both downwards and upwards. The radiated noise is controlled by
such techniques as shielding, grounding, etc. The conducted noise is
damped by filters, but there is always a vestigial ripple present,
superimposed to the fundamental frequency of 50 or 60 Hz. While
conducting such noise, the power lines radiate it too.

The European Union directives concerning EMC (electromagnetic
compatibility) are extrememly tight, but they are only 2 or 3 years
old; therefore, there is still a lot of electronic equipment that does
not conform to these directives. We could hope that things could
improve in Europe during the next years, as the older equipment is put
aside and the newer one is in accordance with the EMC directives. I'm
afraid that such an improvement, if any, will not be very noticeable,
since we are being surrounded by more and more power electronic
equipment. The (great) quantity is replacing the (bad) quality.

We must still consider other factors that generate noise into the
power lines:

- the spikes, harmonics, brownouts, etc. caused by the switching on or
off of large inductive loads, such as motors, induction ovens, etc.
This noise is ever increasing, too;

- the natural causes, such as thunderstorms;

- the leakage currents, around dirty or defective isolators, for
instance, which cause very annoying interferences; etc.

Adding all this, we can understand the concerns of the electricity
companies about the quality of the service they provide.

The possibility of transmitting data through the power grid has raised
much interest some time ago. Maybe there are already some LANs (local
area networks) and some Internet accesses using the power grid, but it
is still in a small scale. The power lines are not well suited to the
transmission of high speed data with great reliability, because they
are a very noisy environment. Therefore, their use will be limited to
small to medium speed data and to some residential or small business
customers.

For the transmission of large amounts of high speed data, without
being affected by electromagnetic noise, the electricity companies in
various countries (including Portugal) have deployed fiberoptic cables
along the power lines. As everybody knows, fiberoptics is imune to
electromagnetic interference. These companies have been using it for
the transmission of their own data and, since the infrastructure is
very expensive, they are now entering the telecommunications business,
to take profit from their own fiberoptic networks.

73s

Fernando de Sousa Ribeiro
Lisbon, Portugal
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