POWER January 2016 - 14

3. A safe alternative. Geomagnetically induced current (GIC) can destroy transformers,
but a GIC-safe unit like the one shown here is designed to avoid damage. Courtesy: Siemens
Energy Management
4. Rapid response. Utilizing a plug-andplay
concept, mobile resiliency transformers
allow operators to recover quickly during
emergencies. Courtesy: Siemens Energy
Management
so it can be avoided. GIC-safe units are
manufactured for up to 200 amp extra DC
capability. The use of nonmagnetic steel
inserts in the tank base and clampings
reduces high saturation levels at extreme
DC levels, lowers eddy current losses, and
prevents overheating due to lower specific
losses. By addressing GIC effects on power
transformers in this way, the grave danger
from outer space is less of a threat.
React. Reactive measures cannot prevent
a blackout, but they give power utilities
an ace up their sleeve in the case of
an emergency. Siemens' solution for fast
reaction is a mobile resiliency unit based
upon a plug-and-play-concept. The main
characteristics of this power transformer
type are its mobility and compactness.
It is a spare unit that utilities can
keep in reserve and transport to a location
where it is needed within a very short
timeframe. The dimensions and weight allow
for transportation on a regular truck
instead of transporting it as an abnormal
load. Unlike installing normal replacement
transformers-which can require a long
time and highly trained staff-mobile
resiliency units (Figure 4) are equipped
with plug-in connectors, bushings, and
cables. Typically, the utility's staff can do
this work easily and quickly thanks to the
plug-in components.
Analysis needs to be done beforehand
Siemens has successfully tested bulletresistant
materials up to .50-caliber M2
ballistics.
To protect transformers from natural
effects, such as geomagnetically induced
current (GIC) from solar storms (Figure 2),
Siemens offers GIC-safe units (Figure 3).
Powerful solar storms are estimated to hit
Earth approximately every 100 years. The
best known and most famous such storm
was the Carrington Event, which shocked
telegraph operators and set some of their
14
offices on fire in 1859. The insurance
company Lloyds has estimated that such
a storm could cause permanent damage to
key transformers and widespread blackouts
of 16 days to two years, affecting up to 40
million people.
In the case of solar storms, GIC flows
from grounded transformer neutrals
through the high-voltage windings into
the transmission lines with some effect on
the transformer. Siemens' intelligent models
calculate critical heating in advance
www.powermag.com
on which locations and which duties the
mobile resiliency unit will serve. Instead
of investing in one spare unit per substation,
it is possible to get a versatile unit
that covers different ratings.
Siemens has already developed such a
solution in cooperation with two different
U.S. utilities. One of them allows reconnection
between the 335/136 kV system
(300 MVA) and the 132/68 kV system (150
MVA) with no oil handling. This solution is
filled with ester instead of mineral oil and
can be transported with oil in the tank,
whereas the other solution relies on partial
removal of mineral oil from the tank
for an even lighter transport weight.
Mobile resiliency units following a
POWER | January 2016

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POWER January 2016

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