One
facet of the Hum is Pumped Storage Hydropower, the Francis Turbine a common
denominator connecting the UK and Italy, by
Dr Chris Barnes, Bangor Scientific and Educational Consultants, June 28th 2013 e-mail manager@bsec-wales.co.uk
Dr Barnes' Homepage Link http://drchrisbarnes.co.uk
Abstract
The
Hum is very briefly reviewed. A possible
connection with the Hum and UK pumped storage hydropower schemes is reiterated
which is reinforced by recent contact with Luca Rizzardi
an Italian acoustician studying the Hum in that country. Francis turbines
appear to be a common denominator. The
predominant frequency recorded does not appear
to be capable of accounting for the pervasiveness of the Hum and is thus
probably symptom rather than cause.
Infrasound directly transmitted and arising by other earth and space
borne mechanisms from power flow oscillations is re-investigated. A connection
with wind power is also realised. Hums
due to these aspects of power systems are hopefully expected to be abated in
future as better wide area real time control is realised.
Introduction
The Hum is a geo-sporadic
auditory phenomenon or possibly group of phenomena which are reckoned to between (2% and 11% of the World’s population
[1].
Contemporary Hums were first documented in newspaper reports in the UK
in the 1970’s [2] and in the USA in
the 1990’s [3]. Hums as distinct from more mundane forms of
LFN are characterised by their apparent lack of traceability and rarely have
been recorded. They are also
characterised by the commonality in the description of the noise given, and the
noise which is said by those afflicted to sound like a distant irregularly
idling engine which cannot always readily be screened out by ear plugs . Hums are often tone matched by musically inclined hearers at
between 36 Hz and 80 Hz and with
quasi-periodic amplitude and frequency fluctuations of between .5 Hz and 5 Hz.
Occasionally both natural
and anthropogenic sources have been found for some Hums. For example a hum on the big island of
Hawaii was traced to volcanic action [4]
and see also Fee et al [5]. Since
volcanoes produce acoustic sound,
infrasound and seismic vibrations, this gives us a possible clue to the Hum. Another US Hum, the Kokomo hum was traced to
separate industrial compressors and fans producing frequencies of 10 Hz and 36 Hz, see Cowan (2008) [6].
Similar to volcanic infrasound,
these anthropogenic sources would also provide infrasound, acoustic
sound and, if ground mounted equipment was involved, seismic vibration.
The Hum used to be an
apparent problem of only the developed Western World which led some such as
Deming to propose it may be associated
with the operations of TCAMO aircraft and indeed in the 1990’s Deming suggested
that the Hum seemed to best correlate in time and space with such operations,
see Deming (2004) [7]. Such aircraft could produce acoustic sound,
infrasound and ELF amongst other radio transmissions.
More recently, however,
in the twenty-first century cases of the Hum have sprung up throughout the
world and in places where TCAMO would not be expected to be in use. Barnes has recently evaluated mapping on the
World Hum database in addition to the locations of visitors to Dawes’ Hum
website. Based on this evaluation it
would appear that the twenty-first century Hum is associated with renewable
electricity generation sites including wind power, pumped storage hydro-power
and solar power [8].
Hums began in the UK in
the 1970’s about the time that pumped storage hydro-power in North Wales and
Scotland was being developed. The
author has shown an association of a
Hum in Bangor and the surrounding area with the Dinorwig
pumped storage hydro-power scheme [9].
It is quite probable that two other well known UK Hums could be
associated with similar schemes. Largs in Scotland has had a famous Hum since the 1980's
which could be associated with the closely located Cruachan hydropower scheme. Loch Ness has a Hum which could equally be
associated with the nearby Foyers
scheme, see Wilson (2008) [10].
Amateur Hum investigator
John Dawes has also had a lifetime belief that the Hum in Britain since the
1970’s is somehow connected with the electricity industry [11]. Dawes even concurs
with the present author that in some facets signals from electricity grids may
even interact in the ionosphere to produce Hums [12]. The present author has
even commented how such interactions may impact the weather and climate[13].
The
Italian connection.
One difficulty with doing
science on the Hum is that it is a highly subjective phenomenon or group of
phenomena where one often has to rely on anecdotal reports. The present author has had the advantage
that he hears the Hum himself and has a live- in subject, namely his wife who
also hears the Hum. Another possible
criticism which could be levelled the present author is that most of his Hum
work has simply been self-published and not peer reviewed, and not reproduced
or endorsed by others nor is he presently directly affiliated with an academic
institution.
Very recently indeed the
author has been contacted by an Itlaian acoustic scientist with a University affiliation,
namely Luca Rizzardi
who has been working with people who hear the Hum in Belluno a province in North East Italy. Rizzardi has also
published evidence of this contact on a well known internet Hum forum [14] .
Furthermore Rizzardi
in his honours degree dissertation, (2012) [15]
has referred extensively to my work and has reached the conclusion that
the Hum in some Italian regions is probably caused by pumped storage hydro
plants. This is a conclusion the present author has previously reached
regarding the Hum in the Bangor Wales region.
Moreover the Italian plants use Francis turbines which are the same type
as those used in the UK. Rizzardi has successfully recorded the Hum about 1 km from
a hydro plant which uses Francis turbines.
The frequencies recorded are in the region of 30 Hz and some infrasound
well below 11Hz the exact frequency of
which is difficult to ascertain given the scales employed. I have previously ascribed on possible
cause of the Hum to infrasound in the presence of low frequency sound and a
flat higher frequency acoustic spectrum [16]. This also seems to be a feature of Rizzardi’s spectrograph. Rizzardi
also comments on the behaviour of the Hum as a function of ground conditions as
influenced by weather. He notes that
the Hum is often weaker or dies out all together when the ground is frozen or
wet but maximises in long, hot dry spells.
This is suggestive of ground propagation over the distance involved and
there is independently published data on the effects of moisture on such
propagation, see Hess et al (1990) [17]. The frequencies recorded are quite close to
those recorded by the present author close to the Dinorwig
Hydro Plant in North Wales and in his house
and neither are they that different from the frequencies associated with
the Kokomo Hum. It is worth noting that Rizzardi
believes the problem frequency to be 30 Hz on the basis of its inclusion in a
spectrum measured locally by the present author and on the premise that a
fairly close frequency of 32 Hz is included in the famous ’56 Hz’ hum spectrum
measured by Moir and his co-worker in New Zealand, see Chapman (2006) [18].
On the other hand, Ruprecht et al [19]in
noise reduction tests for a small Francis turbine conclude that a higher
frequency in the region of 166 Hz is more disturbing. Of course it should be
pointed out that Ruprecht was dealing with plant
operatives and not Hummers (people sensitive to LFN or the Hum).
Considering the frequency
spectrum involved, it is actually the lower of the two frequencies i.e. the
infrasound which would be expected to
propagate considerably further in both the ground (seismically) and air (acoustically) than the 30 Hz
frequency. In other words other than as
a locally experienced noise i.e. local to the power stations themselves, the
present author feels that the observation of 30 Hz is probably more symptomatic
than cause. There is no reason to
suppose that two or more dependent or independent sources, local and distant
could not be responsible for the Hum. For example two separate sources were
responsible for some of the cases of the Kokomo Hum [6].
In the UK some Hums heard
at considerably larger distances from hydro-plants than those observed by Rizzardi. Such plants are, nevertheless, suspected as being
at least in part as being involved [8-10].
It may be necessary to
develop additional or more complex models to explain how this can be and how
the Hum can be such a problem. To a
certain extent this has been done elsewhere by the present author but the sake
of completeness, will be revisited here.
Nevertheless the contact by Rizzardi
and the finding of his work [14,15]
is indeed an exciting development and it
adds considerable credulity to the
present authors’ previous works. The author views it of imperative importance
to explain how the quasi-periodicity of the Hum arises. In this respect an
investigation into pumped storage provides some interesting potential
answers.
Hypothesis: Why is pumped storage is such a problem with
the Hum?
Pumped storage power
stations in general are capable not only
of providing airborne sound and infrasound and coherent seismic
vibration, but also in line with other renewable energy systems such as wind
power their output waveform is notoriously unstable and may contain voltage and
phase flicker. The resultant electromagnetic signals will also have a
degree of coherence with the acoustic, infrasonic and seismic signals and may be capable of reinforcing such signals i.e. that which is the Hum at a distance either by interaction with
the atmosphere, the ionosphere or lithosphere or all three. The resultant infrasonic signals may also be
capable of exciting pulsed room resonance directly in buildings or as a result
of Helmholtz type resonance in
underground pipes or over ground
chimneys attached thereto [20].
Most pumped storage power
stations with a high head employ Francis turbines [21-23]. Francis Turbines
are notorious for pressure and power fluctuations due to hydrodynamic
hydro-acoustic oscillations of the
vortex rope often at infrasonic
frequencies and often with complications due subject to cavitations and or
elbows or bends in the draft tube, see Fanelli (1989)
[24]. In some cases severe self oscillatory
hydro-acoustic resonance, see Susan-Resiga et al (2006) [25]
and Nicolet and Herou (2006) [26] or a similar condition with
narrow band acoustic emission can occur, see Karavosov
et al. Sometimes this can lead to
catastrophic failure of the turbines, see Bashnin
(2013) [27]. Francis turbines can also suffer from
transient effects, see Nicolet et al. (2002) [28].
An almost unique feature
of the Francis turbine is that oscillations of the penstock and discharge
pressure can be excited with a rope
frequency close to one of the eigen
frequencies of the electric system, and particularly at around half load and
due to effect in the draft tube they are capable of acting non-linear oscillators with dynamic hysteresis, see Fanelli 1996 . Dorfler (PhD Thesis 1982) [29] has also confirmed that pressure fluctuations at partial load
in reversible Francis Turbines, i.e. of the type used in pumped storage
hydropower, are irregular. The power
plant close to the author's home has all these features, it has been shown it is
non-linear, multivariate and time varying, see Mansoor
et al (2000) [30]. There can under some instances be increasing
instability in the reverse pump mode, see Gong et al (2012) [31].
Such a mode is usually used at night-time to make use of cheap electricity.
Night-time is when most Hum is experienced.
Some attempts have been
made to control Francis turbines with
either jet control, see Susan-Resiga et al ( 2006)[32] or artificial neural network (ANN) systems, see
Kishor et al 2007 [33]. In China, frequency
converters have been used at the terminals of pumped storage plants to minimise
these sorts of problems, see Galasso (1991) [34]. In this respect it is
interesting to note that until the advent of wind power, another potential
cause of the Hum, China had no Hum reports, http://www.drchrisbarnes.co.uk/Chinahum.htm
[35]. Kishor (2007) [33] concludes that these problems have
still not been adequately solved.
Thus when large pumped
storage power plants are connected into electricity grid systems, their speed
governor characteristic can dominate low frequency inter-area
oscillations, see for example Gencoglu et al (2010) [36]. Power system oscillations generally lie in
the range 0.1-0.8 Hz, see Klein et al (1991) [37]. The present author
sees this as crucial to explaining the pervasiveness of the Hum, in that all
transformers and synchronous machines on a network will be subjected to the
effects of these, as will electrical
ground currents and power line harmonics radiated into space.
In addition to pumped
storage systems, wind farms are now been
shown to provide huge inter area oscillations, see Brownlees
(2006 and 2007) and Wilson et al (2011) [38]. Perhaps then not surprisingly, the present author has shown
contemporary Hums to be more or less exclusively limited to parts of the world
where renewable energy systems are employed.
The frequency range of
seismic signals from hydro-plants and the frequency range of power-systems
inter-area oscillations overlaps. This
range is also the range of reported quasi-periodicity of the Hum. Wilson et al
[38] show that in a power
system with such modes, un-damped oscillations can continue for periods of several hours at a time. Such
time scales are exactly what is
experienced with outbreaks of the Hum. The situation is further complicated because
power systems may also have an effect on natural ULF pulsations of the earth's
magnetosphere, see Fraser Smith (1981) [39]. The precise mechanism is unclear but somehow
by altered mechanism in the ionosphere, the atmosphere, the lithosphere or all
three, the present author has noted that there is nearly always an increase in
the amplitude of the Hum when the IMF ( interplanetary magnetic field Bz) is southward pointing [40]. This not only may add
to the quasi- periodicity and geo and temporal sporadic behaviour of the Hum
but also opens up the possibly that
some individuals may perceive the Hum by senses in addition to audition. Such findings may also account for why some
facets of the Hum behave as an
anthropogenic phenomena e.g. the weekend effect, and some facets are more like
a natural phenomenon.
Besides problems with the
Hum highlighted above there is clearly
separate concern amongst the electricity industry community regarding the dynamic behaviour of generating
stations in general, see Hung (2007) [41].
For instance GPS synchronised phasor measurement between areas is now
possible to monitor inter area oscillation, see Naoto 2006 [42]. Let us hope better power systems control
features will follow soon as a result, with potentially a consequential
reduction of or elimination of the Hum. In the meantime, the Hum clearly
remains a highly complex and enigmatic phenomenon or group of phenomena. The author's hypotheses on the Hum, although
complex, are perfectly logical and let us hope they will soon be independently validated.
One
proof of their validity would be the automatic reduction of or abatement
of many world Hums coincident with the development of such improved features
which will simultaneously benefit the
power generators with improved safety and efficiency. At least with regard to Francis Turbines Rizzardi [14,15] has provided the first element
of validation.
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