The
Hum: models for generation of and perception of an LFN noise nuisance with intriguing
properties, a facet of renewable energy
systems and their connection with the power grid at both local and more distant
points , by
Dr Chris Barnes Manager at Bangor Scientific and Educational Consultants E-mail manager@bsec-wales.co.uk
First published on-line Tuesday 15th
January 2013
Homepage
http://drchrisbarnes.co.uk
Abstract
The Hum, its LFN like nature, history and
supposed origin in the Worlds power systems and effects are briefly
reviewed. Frequency components in the
Worlds’ power systems are shown as adequate to provide those described for the
Hum. The wasted power in the World’s
power systems is more than adequate to provide the Hum. It strongly modulates the elctrojet. Mechanisms of Hum generation are discussed
and it is shown how the Hum can break out either close to a source of renewable
energy or more distant from it. A
simplified model of Hum reception by buildings is discussed and perception
therefrom by hearing and even deaf persons.
Finally possibilities for mitigation are discussed.
Introduction
The Hum is a geo-sporadic noise nuisance
heard/perceived by an estimated 2% of the world’s population, this figure
probably rises to well over 10% in the 40-70 age groups. The noise, an irregular pulsation like very
low pitched buzz, can be extremely irritating and annoying and in its extreme
even cause stress related illness and sleep deprivation. It is mainly but not exclusively in buildings at night even with the power switched off
and is characterised by the sound of a
slowly and irregularly (quasi –periodically) idling engine and these days is
perceived by the present author as often more sharply pulsing than
musical. Those musically minded hearers
of the first instance of the Hum in the USA, the so called Taos Hum tone
matched it between 30-80Hz and stated that it has quasi-period modulations or
fluctuations of between 0.5 and 5Hz.
Others describe a higher pitched buzzing yet still with the same sort of
underlying modulation. Another
strange facet of the Hum is that is either difficult or impossible to audio
record. Sadly this has pushed the Hum,
for some, into the realms of Science Fantasy. This paper, as with the other
works of the present author, aims to demystify the phenomenon.
Everything but power systems has
officially been blamed for the Hum. Scientists at Southampton University
concluded it is simply distant noise.
Wikipedia blames amongst other things colliding waves under the
ocean. Applying critical thinking one
immediately wonders why then distance noise or ocean waves shouldn’t cause the
Hum in the bulk of Russia and Africa and other places which either don’t or
until recently haven’t experienced the Hum.
Contrasting all kinds of infrastructure
between places that don’t and do experience the Hum and using world mapping it
has recently been shown that the Hum is best correlated with sites wherein
there is connection of renewable energy to the power grid. Long time amateur Hum investigator John
Dawes has suggested power systems may be to blame since the first Bristol and Largs Hums in the UK in the late 1970’s and early 1980’s
but has never been able to be specific about which elements of such systems
were the cause, instead John has referred to the general upgrading of the grid
which took place in that era. John does
however have quite a controversial theory of how the Hum might be perceived in
terms of gravity modulation. The present
author can see at least three physical mechanisms as to how this can occur but
not everyone might understand or agree.
It is imagined that John came up with his hypothesis to account for lack of audio recordings and to explain how some deaf people claim to hear the Hum
(and presumably describe the same noise as hearing people) and as to accounting
for how the Hum is sometimes difficult to screen with ear plugs.
The present author feels we now should
re-examine models of Hum to see if any simpler models can apply to perception
in hearing people or if additional facets are needed for or enhance perception
generally.
Hum
generation
First we must ask is it feasible to accept
the notion that the power grid with connected renewable energy sources is the
cause of the Hum?
Two questions need to be asked. Firstly is
the power grid a big enough source of energy?
Secondly does the power grid provide the correct frequency
elements?
The world’s energy grids now carry power
in the order of several TW of which about 200 GW is wind power. Loses are reckoned to be about 7% of which
known loses amount to 6.6%. This leaves 0.4% or about 20GW.
World power grids are cable of
radiating electromagnetic energy, airborne acoustic energy and ground-borne
seismic vibrations presumably this 20GW is distributed between the three.
It is interesting to compare the energy in
the grid with lightning. It is estimated that a moderate thunderstorm produces
about 500MW or power. There are about 2000 thunderstorms on earth at any one
time =1TW. Thus the world’s power grids
exceed this figure.
Thunderstorms influence space weather by
producing magnetospheric whistlers which can be
received as VLF signals on earth. Power
line harmonics and even ripple signals injected into power lines can also
influence the magnetosphere and be received anywhere on earth.
The author thus feels it is fair to
conclude that the power grid is a large
source of energy to provide a Hum or Hums over wide areas. Consistent with this is that some outbreaks
of Hum occur at quite a distance from power lines or electricity distribution
equipment. Kero
at al (2004) have stated that in the vicinity of
power lines, their harmonic signals are decades above those of natural signals
due to global lightning discharges.
Even the magnetic component of the weak ripple control signal at 1050 Hz
Dunedin New Zealand can be detected by the Demeter Satellite.
Dealing with the second question, it can
be shown that power grids contain exactly the right range of frequencies for
the Hum and sharply pulsating behaviours.
Firstly they contain a frequency of 50 or 60 Hz and its entire harmonics
in various proportions. These can be
radiated in all or any of the forms detailed above. Other frequencies can be supplied as a result
of inter-harmonics, sub –harmonics and injected control frequencies such as
those due to ripple control and cyclo-control.
The Hum is described as having
quasi-periodic modulations in the range 0.5-5Hz. Power systems can now supply
the same which will appear manifest as frequency and voltage fluctuations. Prior to the mid 1970’s power systems
oscillations were not recorded in Britain, neither was the Hum. At about the advent of the installation
of pumped storage schemes, power systems oscillations of about .5 Hz were noted
across the entire UK network. Intra
plant oscillations can also occur at 2-3 Hz. Local mode generator frequency
swings occur at 1-2 Hz. Inter area oscillations occur at 1 Hz or less and
finally torsion mode generator shaft oscillations can occur at anywhere between
10-46 Hz. Complicating the situation
for people living near Pumped Storage plants there will also be hydro-dynamic
standing pressure oscillations between 2-3 Hz, these cause both hydro-acoustic
pressure and initiate power oscillations (Koutnik et
al 2006). For wind turbines there is
also infrasound at blade crossing frequencies and coherent voltage flicker effects
at the same frequency.
Finally the Hum has become ‘pulsier’ in recent years.
Power systems harmonics have also become ‘pulsier’
due to the use of more solid state switching, frequency and voltage
compensation, AC/DC converters, Solar PV and wind-turbine inverters. On the
super grid SVC’S dominate for creating harmonics but on the lower voltage
networks embedded generation and domestic and commercial loads dominate
(Lundquist –PhD Thesis Chalmers University of Technology, Sweden). In the specific case of Solar PV
converters, the panels themselves also have the undesirable capacity to act as
radio antennas thereby picking up additional unwanted pulses from mobile and
other communication networks, which can on occasion appear in the inverter output
waveform.
Another potential complicating factor for
the Hum is the way in which the National Grid is now handling dynamic load
response. Domestic refrigerators (since 2009) and Supermarket heating and
ventilation equipment (since 2011) are now being used to this effect. Since effectively they are a reactive load
dynamic in dynamic response this too will increase the harmonics present.
Many loads in Britain are switched by the
BBC Radio 4 Long wave Radio teleswitch. This doesn’t
just send out a message to change Tariffs but is constantly signalling devices
thorough the electricity network.
A ripple control system called Pulsadis has been operated by EDF Energy in France for some
30 years and a similar system called VDEW operates in Germany. These signals start late at night and persist
until morning for Tarrif control. Similar systems
operate throughout Europe and Australasia.
Signals from these can be received together with mains harmonics by
radiation and
ionosphere reflection over huge distances. It is not known is Pulsadis
etc. features in the Hum or in its intensification but parametric mixing is
always a possibility.
Inter-harmonics are as relevant to the Hum
as harmonics and sub-harmonics and may be caused electric motors, wind
turbines, static frequency converters and mains-mark systems (Hanzelka and Bien 2004). Hanzelka and Bien also describe inter-harmonics
specifically as ‘a source of acoustic noise’.
Hum
perception – hearing person with building ‘amplification’
The present author has previously shown
that different acoustic frequencies exist inside and outside buildings and on
different walls and windows of buildings.
Buildings amplify background sound by room resonance. The notion is that any Hum arriving may
arrive by more than one path. In the simplest sense, airborne sound and seismic
vibration can either arrive directly from any piece(s) of hardware in a power
system carrying the relevant frequencies,
various combinations of which have been previously shown by the present
author to elicit the Hum especially if the 50 Hz component is either pulsating
or is not constant in frequency or amplitude (refs) . The seismic component will set the building
walls into forced or resonant vibration.
An alternative hypothesis is that if there
exist strong power system ground currents or electromagnetic fields then either
metallic parts of the building and/or the underlying rock might produce sound
and vibration by electro or magneto –seismic conversion, the latter which can
also enter the building concerned.
Ground currents are typically caused by phase imbalance on power grids.
Wind farms are notorious for causing such imbalance.
Thus the Hum might be expected to be more
pronounced then either near to the source of pumped storage plants, near to
wind turbines, near to industrial sites where there are increased levels of
harmonics or at the end of a long transmission line under a large load. Sometimes Hums may occur at other nodes in
power systems. It is known that transmission line resonance factors can occur
for fundamentals and harmonics even at line lengths as short as one eighth of
one wavelength (Lundquist). Improvements and new developments in both the
communications and power fields have, for the most part, eliminated the need
for transposing high-voltage power lines at close intervals. In many systems
transpositions are made only at switchyards and substations. Geometric
unbalance of un-transposed power lines leads to residual ground currents in solidly
grounded systems. Changes in diurnal power flows will also change the Hum.
Longer term changes in power flows across the entire country will also
cause sporadic outbreaks of the Hum in
places which haven’t previously suffered and could also bring abrupt cessations
of Hums in other places.
Taking specifically, for example, the Hum
in Bangor and the surrounding area as an example, this maximises at night when Dinorwig is pumping. Dinorwig has
been specifically documented as having oscillatory behaviour in its output
under certain conditions and each of its 6 Francis reversible turbines behaves
differently and is linked to a common water feed with some unwanted coupling
taking place. Water hammer is also a feature. Essentially under these conditions it
represents an ‘industrial’ load on the end of a long transmission line. Wind power also contributes to the
problem. The author has previously
noted that the Hum, at least in Bangor, is worse when certain pairs of Francis turbine
pump units are operational at Dinorwig (refs) and there is excellent evidence in the
Scientific Literature as to why this should be with Munoz-Hermandez
and Jones (2005) stating that ‘the
behaviour of Diniorwig is strongly dependent on the number of units
active’ . Dinorwig also has a physical vibration spectrum which
includes the synchronous machine shaft speed of 8.3 Hz and its harmonics (Pritchard 1998).
Another area specific feature of the
electricity network along the North Wales Coast is the power flows at night and
by day are radically different. The
super-grid and some Scottish Power transmission lines run substantially close
and in parallel path. There is the
potential for unbalance due to induced negative phase sequence voltages.
Perception of this kind of Hum requires no
special bio-properties other than sensitive low frequency hearing and
sensitivity to infrasound (Barnes). Even
though the prime mover is a common one different power grid frequency harmonics
and sub –harmonics all subject to oscillatory and pulsation behaviour for the
reasons above can combine by cochlear non-linearity to form the Hum. By using three field spectrum analyses
(Barnes) one can see the changes in real time which give rise to a particular
Hum. If two or more frequencies are
beating together to give the Hum like effect or if the frequencies are buried
in noise, so called stochastic resonance,
( http://www.sciencedirect.com/science/article/pii/S0006899300024756)
conventional audio recording may not be possible. Presumably this was the case with the
original Taos Hum? It should be stressed
however that with increased computational power available to all since those
days has come the ability to make virtual real time frequency spectrum analysis
and present the results in time, amplitude, frequency colour waterfall display
format which allows weekly pulsating audio signals in noise to be
displayed.
Perception
of Hum by deaf people
There are only anecdotal reports of this,
nevertheless it is worthy of attempting to develop a theory to encompass such
accounts. The only feasible hypotheses
would appear to be (electro) magnetic, gravitational, or depending on the type
of deafness bone conducted sound/vibration.
Such models of Hum perception may also
enhance Hum in hearing people under conditions of stochastic resonance by so
called synaesthesia or duelling of the senses.
In this case this would be duelling between conventional audition and a
form of magnetic or gravitational audition.
At least for the present author who although not deaf has firsthand
experience in Hum perception, the magnetic model would seem most feasible (Barnes)
and has been tested in so far as an anomalous case of hearing Hum like effects
in a vehicle not under power lines (Barnes) or at specific distances from
pulsed radio transmitter antennas (Barnes).
It is not certain if all individuals possess this ability because it
might be linked to ratios of biogenic and mineral magnetite in the body
(Barnes).
Perception
of the Hum in buildings with Solar PV
In the above two cases the Hum would be
expected to be perceived whether or not the local building electricity supply
was energised. The author has
experienced the Hum in buildings with Solar PV.
Solar PV inverters can both receive from and transmit distorted
waveforms to the mains. This is so
called embedded generation. The inverter itself may be the acoustic source and
strong electromagnetic fields will surround it.
The Hum from these sources has the potential to be accentuated because
the solar panels can also act as VHF/UHF radio antennas.
Possibilities
for mitigation/prevention
By better control technology it may be
possible to modify power flow oscillations (http://www.eeh.ee.ethz.ch/uploads/tx_ethpublications/tcsc_damp_sadikovic.pdf). Before Japan had the Hum its main power flow
oscillation frequency was of the order of tens of millihertz and it is doubtful humans would perceive
this. One wonders if it could be an
earthquake trigger however!
It is seen as highly unlikely that the
amount of harmonics and pulses our power grids will diminish any time
soon.
The author is aware of two cases of the
Hum, one in Charlbury Oxfordshire and one in
Woodlands Tyne and Wear which appeared to start after ground-works. It is postulated that these disturbed either
channels for conductivity of power grid seismic signals in some way and/or
ground conductivity and power grid earth current flows.
Either way there is a potential route for
R@D in Hum reduction/mitigation here.