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CONTENT INTRODUCTION

WHAT IS SURGE CURRENT

SUPER CONDUCTOR

MEISSNER EFFECT

FAULT CURRENT LIMITOR

SUPERCONDUCTOR FCL

TYPES OF SFCL

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INTRODUCTION

Modern power system is growing very fast with transformers,generators and large networks.

Faults occur in this system at any time.

Super conductors which have zero resistance is used to protect the system from fault current.

Here we are discussing about different types of super conducting devices

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WHAT IS SURGE CURRENT?

•Maximum input current drawn by the electric circuit

when first it is turn on.

•Also known as inrush current,input surge current or

switch on surge.

•High as 100 times the normal steady state current value

and lasts for less the half normal 60 Hz cycle.

• surge current can cause component damage and/or

failure within the equipment itself, blown fuses, tripped

circuit breakers and may severely limit the number of

devices connected to a common power source 4

Surge current waveform

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SUPERCONDUCTOR An element, inter-metallic alloy or compound that will

conduct electricity without resistance below a certain temperature.

Superconductivity is a phenomenon of exactly zero electrical resistance certain materials when cooled below a characteristic critical temperature. The dutch physist Heike kamerlingh onnes observe in mercury.

Types of Superconductors:

Low Temperature Superconductor (lead,mercury)

High temperature Superconductors (YBCO, BSCCO, LSCO)

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MEISSNER EFFECT The Meissner effect is the expulsion of the magnetic

field from a superconductor during its transition to the superconducting state.

The German physicists Walther Meissner and Robert Ochsenfeld discovered the phenomenon in 1933 by measuring the magnetic field distribution outside superconducting tin and lead samples.

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FAULT CURRENT LIMITOR device which limits the prospective fault current when a

fault occurs.

An ideal FCL should have following features

Have zero impedance throughout normal operation

Provide sufficiently large impedance under fault conditions

Provide rapid detection and initiation of limiting action within less than one cycle or 16ms.

Provide immediate (half cycle or 8ms) recovery of normal operation after clearing of a fault.

Be capable of addressing low faults within a period of 15 seconds

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FAULT CURRENT PROBLEM Occurs when expanding buses

When using large transformers

additional generation from co generators and independent power producers (IPPs)

customers request parallel services that enhance the reliability of their supply but raise: the fault duty

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SUPERCONDUCTING FCL

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HOW SFCL WORKS?when operated below critical

parameters: Temperature (Tc)

current (Ic)

Magnetic field (Hc)

Superconductors have virtually zero resistance

When operated above Tc, Ic, Hc, normal state resistance is restored.

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The inherent ability to switch from virtually zero resistance to a finite value when Ic is exceeded can be used to limit short-circuited, fault current.

This property is utilised in inductive shielded type FCL.

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FCL APPLICATIONS Fault-current limiter in the main position. The fault-

current limiter FCL protects the entire bus

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benifits a larger transformer can be used to meet increased

demand on a bus without breaker upgrades

a large, low impedance transformer can be used to maintain voltage regulation at the new power level.

I^2t damage to the transformer is limited.

reduced fault-current flows in the high-voltage circuit that feeds the transformer,which minimizes the voltage dip on the upstream high-voltage bus during a fault on the medium-voltage bus

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Fault-current limiter in the feeder position. The fault-current limiter FCL protects an individual circuit on the bus.

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Fault-current limiter in the bus-tie position.

The two buses are tied, yet a faulted bus receives the full fault current of only one transformer.

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benifits separate buses can be tied together without a large

increase in the fault duty on either bus.

during a fault, a large voltage drop across the limiter maintains voltage level on the unfaulted

bus the paralleled transformers result in low system impedance and good voltage regulation; tap-changing transformers can be avoided

excess capacity of each bus is available to both buses, thus making better use ofthe transformer rating

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TYPES OF SUPERCONDUCTIN FCL RESISTIVE FCL

SUPERCONDUCTORS AS VARIABLE RESISTOR

SHIELDED CORE SFCL.

HYBRID CURRENT LIMITOR

MAGNETIC SHIELDING TYPE SCFCL

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RESISTIVE FCL Superconductor connected in series with the line to be

protected.

To keep it superconducting, it is usually immersed in a coolant that is chilled by a refrigerator.

In case of a fault the inrush of current and magnetic field take the super conductor into the transition region, thereby the increasing resistance limits the fault current.

The behavior of resistic fault current limiter is largely determined by the length of the superconductor and the type of material used for it.

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Resistive FCL with protective shunt

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SUPERCONDUCTORS AS VARIABLE RESISTORS

Superconductors are strongly dependent on direction of an applied external magnetic field. The resistance of a superconductor can change by several orders of magnitude by applying a magnetic field

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SHIELDED CORE SFCL The shielded core fault

current limiter basically a shorted transformer

The device’s primary coil is normal conducting and connected in series to the line to be protected, while the secondary side is superconducting and shorted

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Operation of inductive shielded core SFCL During a fault, increased current on the secondary

causes the HTS element to quench, resulting in a

voltage increase across L1 that opposes the fault

current.

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HYBRID CURRENT LIMITER Consist of series winding transformer.

Primary winding inserted in series.

Secondary winding connected to non inductively wound conducting coil.

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MAGNETIC SHIELDING TYPE

SUPERCONDUCTING FCL

uses a superconductor to shield the magnetic field generated.

During a fault the magnetic field penetrates the superconducting shield at large impedance.

consists of limiting element, an iron core and a control ring.

limiting element is a superconductive cylinder.

The control ring is added to control the currents of superconductive cylinder in fault conditions.

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MAGNETIC SHIELDING TYPE

SUPERCONDUCTING FCL

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IDENTIFICATION

LTS

•Resistance SCFCLs (fast heating type) Toshiba corp.

Kawasaki, Japan together with Tokyo utility Tepco

has built a 13.2 MVA (66KV/2000A) single phase

prototype a 2-4 GVA device is under development.

•GEC Alstom along with Electrocute de France (EDF)

developed and tested a 7.6 MVA (35KV/210A) single

phase device.

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Current limiting characteristics of Toshiba FCL (Nakade 1994, 35).

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HTS American superconductor corp. (ASC) and sumitomo

electric Industries ltd have produced ling lengths of silver

sheathed wire based on Bi 2223 with a critical current at

77K on the order of 50 KAcm-2.

Siemens have demonstrated a resistive 100 KVA model

base4d on YBCO Films.

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CONCLUSION The purpose of this paper was the study of surge

current protection usingsuperconductors.

The SCFCL offers efficient advantages to power system and opens up a major application for super conducting material.

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Reference www.superconductors.com

KE Gray, DE flower-“superconducting fault current limiter”

IEEE transaction on Applied superconductivity – vol.3, march 1997

www. IEEE.org

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THANKS

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