1

Superconducting Fault Current Limiters

First Friday Club1st April 2011

Gerhard Novak – UK Technical Manager

Joachim Bock – Managing Director, Nexans Superconductors

2

Smart Grid Solutions

3

Fault current

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.

4

Fault current

Such a fault current is dangerous for two reasons:

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.

5

Power Networks in the UK

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

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

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

6

Do we need fault current limiters?

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

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 In the UK our power network is facing new challenges, concepts which have applied for the last 40 years are becoming outdated

• Distributed generation such as

Co-generationWind farms

Solar farms

• Stronger linkage/coupling

AC transmission

DC transmission

“Smart grids”:

consumer = producer

7

Do we need fault current limiters?

The traditional load flow will change as we have sustainable energy sources like wind farms included in our network.

Some of our substations will not have been designed for the maximum short circuit currents which may occur in this new situation.

8

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

9

What do we expect from a fault current limiter

normal operation short-circuit recovery

time

curr

ent

First peak:Stress on

the system

Followcurrent:

Thermal loadAND

Detection

10

The typical use is in applications such as:

Where do we need fault current limiters?

• 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)

FCL

FCL

Transformer feeder

Busbar coupler

High voltage

Medium voltage

11

Fault Current Limiters

What are the available technologies?

Pyrotechnic FCL (ABB Is-limiter)

Solid State Fault Current Limiter SSFCL

Superconductive Fault Current Limiters (SFCL)

Resistive type SFCL

Saturated core type SFCL

12

Pyrotechnic FCL (ABB Is-limiter)

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

13

Solid State Fault Current Limiter SSFCL

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

14

Superconductive Fault Current Limiters

The two most common SFCL systems are

Saturated core type

Resistive Type SFCL

Both have been subject to tests on electrical networks

15

Superconductive Fault Current Limiters

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.

16

Superconductive Fault Current Limiters

Resistive Type SFCL

Drawbacks and advantages:

+ Intrinsically safe+ High limitation level (up to 80%)+ Compact size+ Resistive limiting action - Recovery time

17

Production,workshop,and test area

Office building, and assembly hall

Nexans Super ConductorsHTS system provider

18

Alcatel High Temperature Superconductors

ZF Frankfurt Höchst and GBA Knapsack

Corporate Research & Technology

HOECHST RESEARCH & TECHNOLOGY

Nexans SuperConductors

October 1987

January 1995

January 1998

May 1998

October 2000

October 1999chemistryphysicsmaterial sc. electrical eng.mechanical eng.

Nexans Super ConductorsMaterials – Components - Systems

From R&D to systems

19

buffer2buffer1

substrate

YBa2Cu3O7-x

Bi-2212/ Bi-2223 tape1st generation

Bi-2212 bulk

Y-123 cc-tape2nd generation

Y-123 bulk

HTS material and conductor typesfor industrial applications

20

BSCCO-2212 tubes

BiSrCaCuO

powder

Fault Current Limiter Components

Melt Cast ProcessNexans proprietary process

From powder to HTS-components

21

component module set-up of a phase

accommodationin a cryostat

Basic design of the FCL

•Current and voltage adjustable by modular construction•Fault Current Limiter connected in series with the grid

Connection for adaptation •Current in parallel•Voltage in series

22

Realisation of the FCL

Nexans capabilities encompass the full manufacturing and

installation process

23

ASL, NewcastleENW, Bamber

Bridge

Live on grid10-2009 to 06-2010

Project 1: 12-100 Field test

24

• 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

Project 2: Vattenfall Brown Coal Power Plant- First FCL worldwide in a power plant

25

Project 3: ASL 12-400 Ainsworth Lane (Scottish Power)

System ready testedDelivery Feb 2011

26

Thank you very much for your attentionAny Questions?

Contact Details: Joachim Bock joachim.bock@nexans.com +49 (0) 22 33 48 66 58

Gerhard Novak gerhard.novak@nexans.com +44 (0) 1908 250 821

27

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)

28

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