Fault Current Limiters Using

Superconductors

Name – Jaypal SinghRoll no. – 104021Branch – Electrical(Core)

Contents1.What is fault current?2.Need for fault current limiter3.Characteristics of an ideal fault

current limiter4.Traditional ways to limit fault current5.Superconductors as fault current

limiters6.Types of SFCL7.Comparison between different SFCL8.Advantages of SFCL9.Conclusion

What is fault current?

Fault current is any abnormal electric current that flows through a circuit during the electrical fault conditions like L-G, L-L-G, L-L-L-G, L-L, L-L-L faults.

Fault current may be several times larger in magnitude than the current that normally flows through the circuit.

Fault current limiter is a device which limits the prospective fault current when a fault occurs.

Need for fault current limiter

Increasing demand of power and addition of more generators, transformers and large networks causes higher stress on power system.

Higher stresses results in higher probability of faults.

In near future, networks may reach or exceed the short circuit limits.

Characteristics of ideal fault current limiter

Have zero impedance throughout normal operation

Provides sufficiently large impedance under fault conditions

Provides rapid detection and initiation of limiting action

Provides immediate recovery of normal operation after clearing fault

Characteristics cont..

Fully automatic highly reliable Light weight Compact Low cost Longer life

Traditional ways to limit fault current

Following methods are used to limit fault current-: Circuit breakers with ultra-high fault

current rating High impedance transformers Current limiting fuses Air core reactors Reconfiguration of system by splitting

power buses

New approach using superconductors

Superconductor- It is an element, inter-metallic alloy or compound that will conduct electricity without offering resistance below a certain temperature.

Types of superconductors- Low temperature

superconductors(LTS) High temperature

superconductors(HTS)

Cont..LTS are the substances that

lose all resistivity close to 4K, a temperature attainable only by liquid helium.

Examples of LTS - Lead and MercuryHTS are the substances that

lose all resistance below temperature mainly attainable by liquid nitrogen (70K).

Examples of HTS – YBCO, BSCCO etc.

Superconductor fault current limiter

(SFCL)Superconductor is used because of their sharp transition from zero resistance at normal currents to finite resistance at higher current densities(above critical temp).Parameters for superconductivity- Temperature (T) Current (I) Magnetic field (H)

How do SFCLs work 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.

Cont..

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.

Types of Superconductor FCL Resistive SFCL

Inductive Shielded core SFCL

Resistive SFCL Utilize superconducting material as

main current carrying conductor under normal grid operation

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

Resistive FCL with protective shunt

superconductor

Operation of SFCLWhen a fault occurs, the current increases and causes the superconductor to quench thereby increasing its resistance exponentially.

Inductive shielded core SFCL

Device resembles a transformer with the secondary side shunted by an HTS element

An electrical connection is made between the line and the HTS element through mutual coupling of AC coils via a magnetic field

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.

Applications of SFCLThree main applications areas

are -Fault-current limiter in the main

position - the fault-current limiter FCL protects the entire bus

Fault-current limiter in the feeder position - the fault-current limiter FCL protects an individual circuit on the bus. Underrated equipment can be selectively protected as needed in this manner.

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.

Advantages of SFCL

In comparison to conventional technology, SFCL provide -

Faster response time Shorter recovery timeTime-adjustable response

functions