Superconducting
Fault Current Limiters
First Friday Club
1st April 2011
Gerhard Novak – UK Technical Manager
Joachim Bock – Managing Director, Nexans Superconductors
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Smart Grid Solutions
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Fault current
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What is a fault current?
A fault current is the current which flows during a
short circuit.
At home we have fuses or magnetic circuit breakers
to switch off in case of a short circuit.
In a substation the situation is the same – only the
current is much higher - thousands of ampere.
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Fault current
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Such a fault current is dangerous for two reasons:
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Magnetic forces: during a short circuit enormous
magnetic forces are created which try to move
electric conductors away from each other.
Thermal energy: The high current during a short
circuit heats up all electric conductors in fractions of a
second and can lead to a fire.
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Power Networks in the UK
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Until now, operators of public and industrial
electrical networks could only have limited protection
from high short circuit currents, either by the use of
complicated equipment or overrated components
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Development of distributed generation, such as wind
power, and the ever increasing demands for power
have pushed medium voltage power grids to their
maximum operating limits
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Short circuits can occur more often and are more
likely to cause high, uncontrollable fault currents
which can lead to defects in the electrical systems
and to power failures
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Do we need fault current limiters?
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If we could look into the future we could plan for every substation and
switchgear to cope with the maximum fault current the network will ever
deliver
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But we have to work with our existing network. In the UK our power
network is facing new challenges, concepts which have applied for the last
40 years are becoming outdated
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¾ Win
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¾ Sola
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• Stro
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¾ AC t
ission
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¾ DC t
grids”:
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Do we need fault current limiters?
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The traditional load flow will change as we have sustainable energy
sources like wind farms included in our network.
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Some of our substations will not have been designed for the maximum
short circuit currents which may occur in this new situation.
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Do we need fault current limiters?
Solutions:
1. Upgrade the substation to cope with the new maximum short
circuit current – from mechanical and thermal point of view.
This may cost several million £.
2. Or, add a device which reduces the short circuit current to a
value which our existing substations can cope with
A Fault Current Limiter
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What do we expect from a fault current limiter
normal operation
short-circuit
recovery
current
First peak:
Stress on
the system
Follow
current:
Thermal load
AND
Detection
time
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Where do we need fault current limiters?
The typical use is in applications such as:
• Busbar coupling
• In-line (secondary side of transformer)
House load protection in power plants (a coal power plant
needs 8% of the power created for auxiliary systems)
High voltage
Transformer
feeder
FCL
•
Medium
voltage
FCL
Busbar
coupler
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Fault Current Limiters
What are the available technologies?
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Pyrotechnic FCL (ABB Is-limiter)
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Solid State Fault Current Limiter SSFCL
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Superconductive Fault Current Limiters (SFCL)
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Resistive type SFCL
¾
Saturated core type SFCL
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Pyrotechnic FCL (ABB Is-limiter)
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Existed for 50 years but usage is not
widespread as it has several drawbacks:
- Non fail save
- Safety concerns (explosion)
- No automatic recovery (time!)
+ Can be disabled by software
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Solid State Fault Current Limiter SSFCL
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Still at R&D stage
-
High loss also at standby (high operation cost)
Needs external trigger (Reliability?)
The control hardware is responsible for the function
Complex system
Cost
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Superconductive Fault Current Limiters
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The two most common SFCL systems are
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Saturated core type
¾
Resistive Type SFCL
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Both have been subject to tests on electrical networks
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Superconductive Fault Current Limiters
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Saturated Core Type
Drawbacks and advantages:
- Weight
- DC operation of superconductor
- Low limitation level (approx. 20%) of 1st peak
- Large size
- Oil cooled
- Losses and limiting effect
+ Immediate recovery
+ Intrinsically safe
+ No need to disconnect
This system doesn’t use the special properties a superconductive material has and theoretically
it could be built without using superconductive conductors.
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Superconductive Fault Current Limiters
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Resistive Type SFCL
Drawbacks and advantages:
+
+
+
+
-
Intrinsically safe
High limitation level (up to 80%)
Compact size
Resistive limiting action
Recovery time
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Nexans Super Conductors
HTS system provider
Office building,
and assembly
hall
Production,
workshop,
and test area
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Nexans Super Conductors
Materials – Components - Systems
From R&D
to systems
ZF Frankfurt Höchst and GBA Knapsack
October 1987
Corporate Research & Technology
HOECHST RESEARCH & TECHNOLOGY
January 1995
January 1998
May 1998
chemistry
physics
material sc.
electrical eng.
mechanical eng.
October 1999
Alcatel High Temperature Superconductors
October 2000
Nexans SuperConductors
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HTS material and conductor types
for industrial applications
YBa2Cu3O7-x
buffer2
buffer1
substrate
Bi-2212/ Bi-2223 tape
1st generation
Bi-2212 bulk
Y-123 cc-tape
2nd generation
Y-123 bulk
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From powder
to HTS-components
Melt Cast Process
Nexans proprietary process
Fault Current Limiter
Components
BSCCO-2212
tubes
BiSrCaCuO
powder
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Basic design of the FCL
Connection for adaptation
•Current in parallel
•Voltage in series
component
module
set-up
of a phase
accommodation
in a cryostat
•Current and voltage adjustable by modular construction
•Fault Current Limiter connected in series with the grid
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Realisation of the FCL
Nexans capabilities encompass
the full manufacturing and
installation process
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Project 1: 12-100
Field test
ASL, Newcastle
ENW, Bamber
Bridge
Live on grid
10-2009 to 06-2010
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Project 2: Vattenfall Brown Coal Power Plant
- First FCL worldwide in a power plant
• Installation
10/ 2009
• Commissioning
02.11.2009
• End of field-test
12/ 2010
Second field test
planned with new
superconductor
(tape)
• Significant savings for extension and new construction
• Improved safety for personnel and equipment
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Project 3: ASL 12-400
Ainsworth Lane (Scottish Power)
System ready tested
Delivery Feb 2011
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Thank you very much for your attention
Any Questions?
Contact Details:
Joachim Bock [email protected] +49 (0) 22 33 48 66 58
Gerhard Novak [email protected] +44 (0) 1908 250 821
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Superconductivity
Superconductivity – what is that?
Superconductivity is a physical phenomena which happens at very low
temperatures (-270 to -273°C) – at this low temperatures the resistance of
an electric conductor drops to zero.
This phenomenon is known since 1911 but it is only recently (1986) that
materials have been developed which show this phenomena at higher
temperatures - The so called ‘high temperature superconductors’. The
temperature is still not high – as we speak about 85K
(approx -188°C) – but this temperature is easier to reach than -273°C…
Where do we find superconductors? Wherever the need for a strong magnetic
field is (CERN particle accelerator, Magnet resonance tomography) and
where energy needs to be transported with low resistive losses
(superconductive cables)
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Superconductivity
As the resistance of a superconductive material is zero it will not heat up
during normal use.
But there is one other physical limit – the current density. (Ampere per mm2)
The current density of a superconductor is approximately 1000 to 10000
times higher than that of copper – if the current flow goes above this limit
the superconductor starts to heat up and instantly loses its’ special
superconductive properties until it is cooled down to 85K again.
This effect is used for the SFCL
back up
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