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it is the closing down of some major
industries, with more closures on
the way.
Energy demand is not the reason for
rising electricity prices – it’s peak demand.
Peak demand occurring for short
times will strain transmission and
distribution systems, requiring greater
capital expenditure and prompting
tariff increases. Figure 1 (overleaf)
shows what’s been happening to energy
demand in peak gigawatts over the
past 17 years.
However, real demand is measured in
kVA, MVA or, in the case of the graph, in
GVA to keep things on the same scale.
That measure is determined by power
factor. There is every reason to think
that the power factor issue is not going
away, and this is why:
>
growth in HVAC; and,
>
growth in ‘electronic’ loads including
lighting.
They add to the old-fashioned notion
of power factor.
They also add to the bill, as electricity
prices now include a kVA demand
charge. The poorer the power factor
is, the more you get slugged, because
everything that depends on good
voltage regulation in the transmission/
distribution system depends on
flattening that demand.
ELECTRICITYMETERS
Material published by the distribution
sector, and companies selling power
factor correction gear, includes images
of beers and coffees topped with foam.
The slogan is ‘You also have to pay for
the foam.’
Then there’s the right-angle triangle
explanation for the more technical
reader. The triangle is the graphical
explanation that:
kW² + kVAr² = kVA²
There’s a sharp definition of what
a kilowatt is – you heat water with
it – and torque multiplied by revs for
mechanical loads driven by motors.
There is no immediately sharp
definition for the other terms. That’s
because of the prevalence of
electronic loads including HVAC, and
the increase here and there due to
wind farms and solar farms with
increasing capacities being connected to
distribution networks.
The kVA measure depends not only
on the meter but also on the quality of
power being delivered.
Installations can’t be allowed to
spew out more than a certain level
of harmonics or there’s trouble with
the distribution company. That’s why
so many installations now feature
harmonic filters.
Then there’s power factor. Capacitor
banks or active filters, or a combination
of the two will improve the power
factor – you hope. It may well, but not
necessarily as much as ‘calculated’ from
the right angle triangle theory.
It’s how kVA is measured that
influences the demand charges. To put
it succinctly: irrespective of the
metrology employed in the electricity
meter, kVA represents your current
(including your harmonics) multiplied
by the power supply’s voltage (including
its harmonics).
The basic metrology for kVA is
the summing of small time-slice,
synchronously sampled voltage by
current multiplications.
The more distortion by way of voltage
harmonics there is in the supply voltage,
the more the kVA becomes.
If you would like to know the nitty
gritty, there are publications explaining
the IEEE 1549-2010 methods on how to
measure kVA.
However, it’s doubtful that a local
poles and wires outfit will be able to
answer the kVA theory of measurement
question. Furthermore, after December
2017 it won’t be their business to
automatically supply the electricity
meters. That will be the business of
meter co-ordinators (MCs), a separate
type of company created by the Federal
Government’s Power of Choice program.
In short, the kVA portion of the bill
is determined by a less than precise
kVA computation (certainly on the
part of the consumer) and a precisely
known tariff.
CANWE FORGET KVAR?
The ‘froth’ factor or real power factor
is simply kW divided by kVA.
But we can’t forget the kVArs.
There’s the kVAr which, when too high,
causes network instability. This is the
‘displacement’ kVAr, responsible for the
displacement power factor.
Distribution companies want
customers to keep to acceptable limits.
It’s part of the kVA, but only a part, as
explained above.
What sort of effect from harmonic
distortion can you expect on kVA
demand? It’s not necessarily dramatic,
but it can tip you over the edge if
there’s a maximum kVA beyond which a
punitive rate applies.
Additions to kVA can be major if
there is substantial voltage distortion.
That is something you should test
thoroughly. The procedure can be
trying. You need to switch off loads
likely to influence the voltage distortion
then check voltage distortion at the
switchboard. For a new installation it’s
easy – do the test, then connect.
And before we let the topic go, there
There’s business to be had from the more modest
consumers of electricity.
BY
PHIL
KREVELD