Electricity + Control August 2017

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13 Electricity + Control AUGUST 2017
• Harmonics: These generally result from the
load source and propagate themselves back
into the local and distribution networks. De-
pending on the type and severity of the har-
monic, it can result in over heating of the neu-
tral conductors, premature tripping of circuit
breakers and possible reversing of electrical
motors. The harmonics also influence the pow-
er factor of the plant and can be responsible for
the failure of the PFC capacitor circuits
With these quality of supply problems, it’s easy to
see that simply having a back-up power solution isn’t
enough. Businesses that rely on power – and, let’s
face it, they virtually all do – can find themselves
faced with more than just a power outage. Damage
caused by surges, sags, spikes and harmonics can
costs businesses hundreds of thousands of rand in
equipment repair and loss of productivity.
UPS – the answer?
UPSs are seen as the ‘one solution fits all’ option to
protecting equipment and, while that’s not entirely
true, it’s also not quite so simple. There are a lot of
factors that influence what type of UPS is required,
such as the nature of the equipment being sup-
ported, the load, how critical maintaining constant
power supply is, and the electrical environment, as
indicated above. As can be seen from above, one
requires continuity of supply, voltage stabilisation,
filtration for the spikes and harmonics and galvanic
isolation in order to be called a power conditioner.
There are essentially three types of UPS, start-
ing with the most basic, which is your offline UPS.
These, offer just enough time to shut down equip-
ment – usually 3 – 4 minutes and are commonly
used to support things like office computers. This
type of UPS offers limited protection from surges
or voltage instability and are as susceptible to be-
ing damaged themselves by poor quality power.
The second type is your line interactive UPS,
which has a small amount of power conditioning
built in, such as voltage stabilisers to help regulate
input power and has an element of line filtering and
surge protection to reduce spikes and dips. Very
<<Author>>
Kevin Norris, Solutions
Architect, Jasco
Power.
popular in small IT environments, these units are
reasonably priced and typically offer about 15 min-
utes of back-up time – just enough to facilitate auto-
matic shutdowns of systems and servers. Howev-
er, the extent of power conditioning is still limited.
The last type of UPS technology is the true, on-
line double conversion UPS, which is designed to
run 24 hours per day, with large battery banks for
extended back up during power failures.These UPSs
act as intermediaries between the grid and equip-
ment, offering good power conditioning and can tol-
erating most surges, sags and fluctuations in supply.
However, experience and the results of many
site surveys have shown that UPSs are not com-
pletely effective on their own, and need to be sup-
ported by additional power conditioning equipment
such as voltage stabilisers for extreme fluctuations
in input voltage. The use of isolation transformers,
offers very good common mode protection and can
help to reduce or increase incorrect supply voltage
conditions and are able to contain harmonic condi-
tions in a network. It is also important to understand
that a UPS is not a lightning protector and that a
lightning protection device should be added to all
UPS installations to protect both the load and the
UPS from failure due to excessive lightning activity.
Conclusion
Finally, it is very important to refer to the UPS man-
ufacturers electrical and environmental operating
specifications, as too often the level of harmonics
present and the extreme deviation of the power
factor from unity can result in the inability of the
UPS to function correctly and results in both the
load and UPS being permanently damaged.
Businesses,
particularly those
for which quality
of supply is
critical, must plan
their solutions
properly.