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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 longdistance lines and complex intermeshed grid structures that must
contend with both quasi-stationary
low-DC currents and high-amplitude
geomagnetically induced currents
(GIC) caused by recurrent solar
magnetic disturbances. Siemens
accepted the challenge and offers
specially adapted design measures
to improve 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.
Solar wind effects:
•GIC turbulence: can last for days,
with alternating intensity and
polarity
•Basic GIC level 10–50 amp DC
per phase for minutes to hours
•Extreme GIC peaks up to
200 amp DC per phase 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
• High latitude countries (Canada,
Scandinavia, Russia) are particularly
vulnerable to magnetic-field 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 October 30, 2003, hundreds of thousands of people in the southern Swedish
city of Malmö lost power. Many accidents
occurred because the traffic lights failed.
Telephone and railway systems were also
compromised, causing significant economic loss. Siemens Transformers has been
researching this phenomenon since 1989,
motivated by the GIC-induced collapse of
the Canadian Hydro-Québec power grid.
Since this GIC event, Siemens Transformers
has been researching the phenomenon
and developed GIC-safe power transformer
designs to reduce the risk of electric
outage 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 is conducted from the transmission
lines to the HV windings over the grounded
transformer neutral, which can have an
impact on the transformer.
Grid disturbances
• 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-current heating in
specific metallic parts
• Tie bars at the core are most vulnerable
(even at low DC levels)
• Clamping plate, tank cover, and
windings are vulnerable only at
especially high DC currents
How GIC calculations led
to GIC-safe power transformer
solutions
From calculation to design
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 under load conditions
• Reactive power consumption with
harmonic wave analysis
For a detailed examination of different
GlC effects, two different calculation
models are used. With the transient finite
element method (FEM-3D), hot spots in
structural parts can be precisely localized.
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 provide the option of
calculating 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 injection tests with hotspot
measurements
• A DGA analysis before and after testing
with specified acceptance levels and
built-in temperature sensors is used
to verify the success of the GIC-safe
power transformer design.
• Harmonic and reactive power can be
measured.
“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
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
Siemens AG 2016
Energy Management Division
Freyeslebenstrasse 1
91058 Erlangen, Germany
Siemens AG
Transformers
Katzwangerstrasse 150
90461 Nuremberg, Germany
Printed in Germany
Dispo 19200
TH 101-150745
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