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Designed to withstand
Siemens GIC-safe power transformers
Reliable under exceptional
network conditions
In every power supply network,
transformers are strategic nodes.
They are in operation in long­
distance lines and complex inter­
meshed power grids that must
contend with exposure to quasistationary low-DC currents and
even high-amplitude geomag­
netically induced currents (GIC)
caused by recurrent solar magnetic
disturbances. Siemens accepted
the challenge and offers specially
adapted design measures to im­
prove transformer performance
and resistance capability under
exceptional network conditions.
Areas of GIC impacts
GIC is a risk for electric infrastructures
worldwide. The moment, intensity,
and location of a GIC event cannot
be precisely calculated. The shortest
­solar cycle is predicted for every
eleventh year, so the next GIC event
is forecast for 2012–2014.
Solar wind effects:
•GIC turbulence: can last for days,
with alternating intensity and
polarity
•Basic GIC level 10–50 amp DC
for minutes to hours
•Extreme GIC peaks up to
200 amp DC in transformers
Danger from outer space won’t harm Siemens power transformers –
designed to withstand GIC events from solar wind and sunspots
GIC –
geomagnetically induced currents
Space weather events like solar wind and
sunspots cause geomagnetically induced
currents. Electrically charged particles in
both the magnetosphere and ionosphere
experience enormous variations, influencing the earth’s magnetic field.
• Coronal mass ejections create solar
wind and charged particles
• Interactions with the earth’s
magnetosphere
• Variations in the earth’s magnetic field
of low (quasi-stationary) frequency
(0.1 to 0.001 Hz)
• Solar events follow 11-year cycles
• Solar cycles of higher magnitude
predicted for 2012–2014
• High latitude countries
(Canada, Scandinavia, Russia) are
particularly vulnerable to magneticfield turbulence (aurora borealis)
Historic GIC events –
the start of Siemens’ research
In the year 1859, there occurred a solar
superstorm known as the Carrington
event, which was the most powerful solar
storm in recorded history. Auroras were
seen all around the world, telegraph
­systems worldwide failed, pylons threw
sparks, and telegraph paper caught fire.
On March 13, 1989, a geomagnetic storm
caused the collapse of the Canadian
Hydro-Québec power grid and, in a few
seconds, six million people were left without power for nine hours, with significant
economic loss. Since this GIC event,
­Siemens Transformers has been researching the phenomenon and developed GICsafe power transformer designs to reduce
the risk of electric o
­ utage caused by
these events.
GIC and the grid
High-voltage overhead transmission lines,
earth-return paths, and grounded highvoltage HV windings are linked to geomagnetic field changes (dB/dt ... 200 to
400 nT/minute).
The magnitude of GIC depends on:
• Induced voltage (up to two to 10 V/mile)
• Network topology
• Resistivity of soil
• High-voltage transmission line
resistance
• Angle between HV transmission line
and magnetic field
GIC flow from grounded transformer
­neutrals through the HV windings into
the transmission lines with some impacts
on the transformer.
Answers for energy.
Back effects from transformer
on the grid
• Higher magnetizing current – reactive
power consumption up to 50 MVA
• Harmonics may occur
hotspot temperature in winding
75
10,0
9,0
8,0
70
7,0
65
6,0
5,0
60
4,0
3,0
55
2,0
1,0
50
0
5
10
15
20
25
30
35
time in min
40
hotspot @ 120A DC
hotspot @ 200A DC
45
50
55
60
0,0
loss factor
hotspot temperature in K
EARTH SURFACE POTENTIAL
GIC effects on transformers
• Additional noise (15 to 20 percent
enhancement) with characteristic
spectrum: odd multiple frequencies
of 60 Hz in spectra ... 300 Hz; 420 Hz).
Example: Noise increase with
2 amp DC/Phase is 15 dB(A)
• Tank vibrations
• Critical eddy-loss heating in specific
metallic parts
• Tie bars near core are most vulnerable
(even at low DC levels)
• Clamping plate, tank cover, and
windings are vulnerable at extremely
high DC levels only
How GIC calculations led
to GIC-safe power transformer
solutions
From GIC calculability to transformer
design reality
Siemens Transformers began its GIC
research in 1989, intensified the development of GIC-safe power transformers,
and has been conducting out case studies
and specific GIC tests since 1996. While
the actual GIC event still cannot be calculated, today the calculation of their
potential impact on transformers is highly
advanced in terms of:
• Heating of different structural parts
• Winding hotspot increase for any given
GIC on/off load cycle
• Reactive power consumption
in combination with analysis
For a detailed examination of different
GlC effects, two different calculation
models are used. With transient FEM-3D
(finite element method), hot spots in tie
plates and clamping plates can be precisely
identified, where eddy current heated
these metallic parts. For GIC effects on
the transformer in connection with the
grid, transient electromagnetic network
models are required. In this case, the
transformer is modeled as a magnetic
subsystem of the total grid to permit the
determination of the reactive power consumption and harmonics of the current.
In addition, network models deliver the
potential to calculate eddy losses in single
winding parts for a detailed winding
hotspot calculation.
Verification through testing
The GIC-safe transformer is then put
through its paces in the test lab.
GIC-withstand capability is verified by:
• DC and GIC injection tests with hotspot
measurements
• A DGA analysis before and after testing
with specified acceptance levels is used
to verify the success of the GIC-safe
power transformer design.
“For knowledge, too, itself is power”
In GIC cases, Siemens’ expertise is unique
and ensures GIC safety down to the
smallest detail:
• Specific steps to avoid critical heating
caused by GIC are calculated using FEM
• GIC-safe transformers are
manufactured for up to 200 A
extra DC capability
• The use of non-magnetic steel inserts
in tank base and clampings reduces
high saturation levels at extreme DC
levels, lowers eddy current losses, and
prevents overheating due to lower
specific losses
Trick the GIC
Since Siemens has succeeded in addressing GIC effects on power transformers,
the grave “danger from outer space” that
can seriously damage our electrical supply
is no longer a threat. To keep customers’
power grids going, the choice must be the
safest transformers and shunt reactors
that can endure GIC impacts even at
­extreme DC levels.
Published by and copyright © 2014:
Siemens AG
Energy Sector
Freyeslebenstrasse 1
91058 Erlangen, Germany
Siemens AG
Energy Sector
Power Transmission Division
Transformers
Katzwanger Strasse 150
90461 Nuremberg, Germany
www.siemens.com/energy
Power Transmission Division
Printed in Germany
Dispo 19200
TH 101-140116 472581 DB 0714
siemens.com/energy/transformers