Transient Performance Improvement of Microgrid by a Resistive

Superconductiong Fault Current Limiter

Feng Zheng, Lie Chen,member, IEEE,shichun Li, Yang Liu,and Yuxiang LiaoVol.25,no.3 JUNE 2015

By-Rohan V. JainRoll no. 152642

Guided by-Dr. C.H Vainkaih

Contents• Introduction to Microgrid• Need for fault current limiter on microgrid• Characteristics of an ideal fault current limiter• Traditional ways to limit fault current• Why Superconductors as fault current limiters• Types of SFCL• Resistive SFCL• Modeling of SFCL in Microgrid Application• Explanation using MATLAB Simulink• Conclusion

Microgrid

Need of fault current limiter• Increasing demand of power .• addition of more generators, transformers.• Frequency matching problem with local sources and utility in

microgrid.• large networks causes higher stress on power system.• Connection of Distributed Generation in Microgrid• Cascading of fault can turn to blackout.

Characteristics of an 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• Fully automatic • highly reliable• Light weight• Compact• Low cost• Longer life

Traditional ways to limit fault current• Current limiting fuses-• Circuit breakers with ultra-high fault current rating.• High impedance transformers• Air core reactors• Reconfiguration of system by splitting power buses

Why Superconductors as fault current limiters

• Have zero impedance throughout normal operation.• Online power loss reduced.• Provides sufficiently large impedance under fault conditions.• Provides rapid initiation of limiting action.• Provides immediate recovery of normal operation after clearing fault.• Fully automatic.• Fast and smooth transition from Grid connected to islanded mode of

operation in Microgrid.

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.• 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 resistive SFCL.

Types of Superconductor FCL• Resistive type SFCL

• Inductive type 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.• Shunt Rsh needed to avoid hot spots during quench, to adjust the limiting current

and to avoid over-voltages due to the fast currentlimitations.

Modeling of Resistive SFCL

Rn= impedence being saturated at normal temprature

t0=quench starting time

t1 & t2 =first and second recovery starting time

• SFCL has recovery time less than 0.5s so as to matchup with auto reclosing operation.

Material and working

• High Temperature Superconducting materials are used.

• Bismut-Strontium-Calcium-Copper-Oxide

(BSCCO) Bulk Bi series Bi-2212 (2G)• YBa2Cu3Ox(YBCO) (Yittrium-Barium-Copper-Oxide) 2nd

generation(2G) Widely used for Resistive SFCL because 1.less recovery time(2ms to 4ms) 2.higher current limitation than Bi series

Application of Resistive SFCL on Microgrid’s transient performance.

• PCC- point of common Coupling between main network and microgrid.• Energy storage device served as Master DG• DG has mainly two control pattern 1.P-Q Control 2.V-f Control

Schematic of typical microgrid integrated with the SFCL

• Based on fault condition, SFCL need to switch microgrid from grid connected mode to islanded mode very fast. • Due to rapid quenching characteristics of SFCL, fast trigger signal will

send to collection system for DG’s control switching

• Under Normal condition Grid connected mode-DG will use P-Q control• Under Fault condition Islanded Mode – DG will use V-f control

Microgrid Operating Modes• Grid Connected Mode:

• Utility grid is active.

• Static switch is closed

• All the feeders are being supplied by utility grid.

• Island Mode:

• Utility grid is not supplying power

• Static switch is open.

• Feeder A, B, C are being supplied by Microsources.

• Feeder D (not sensitive ) is dead.

BLOCK DIAGRAM

• 1&3- to achieve master DG’s (P,Q) control

• 2&4- to achieve master DG’s V-f control

Control strategy of the energy storage device in consideration of the Resistive SFCL’s trigger signal

Simulation study

• The simulation parameter

Creating a fault at middle of connecting lines• in simulation set suppose fault at t0=1s and last for 100ms and the

steady state switch will be operated at t=1.1s• In this duration Microgrid has to change from grid connected to

islanded mode.• Before fault happens, MG is connected to main network and exchange

some power.• After the fault , variation in SFCL voltages and current and current

limiter are shown.

Fault current at PCC and voltage change at SFCL terminals Superconductor mechanism

• Applying to SFCL can maintain PCC voltage as 0.5pu compared to that PCC voltage falls below 0.08pu without SFCL.• Employing Resistive SFCL can makes MG smooth transitions between modes.• Fast detection of fault and gives activation signal to control mechanism in quarter of

power frequency cycles.• Reliability of Power supply increses.• SFCL’s current liming Resistance effectively absorb the surplus power, so as to

maintain frequency variation.

Observations from SIMULINK

Future scope

• SIEMENS has started research on that and trying to make use it in real power system.• 100kVA fully functioning model have been tested by SIEMENS.• Overcurrent relays employed with SFCL in power system can prevent

its malfunction.

conclusion• SFCL provides quick system protection during a severe fault.• SFCL reduced the level of short circuit Fault current which is caused

due to fault in Grid.• It is fast acting FCL.• Causes no power loss during steady state condition.• Provides the system effective damping for frequency oscillation.• Improves the transient stability of Power System.

References• M. D. Ainslie et al., “Superconducting fault current limiter design using parallel-connected YBCO

thin films,” IEEE Trans. Appl. Supercond.,vol. 19, no. 3, pp. 1918–1921, Jun. 2009.• S. M. Blair, C. D. Booth, G. M. Burt, and C. G. Bright, “Application

of multiple resistive superconducting fault-current limiters for fast fault detection in highly interconnected distribution systems,” IEEE Trans.Power Del., vol. 28, no. 2, pp. 1120–1127, Apr. 2013.

• J. A. Peças Lopes, C. L. Moreira, and A. G. Madureira. “Defining controlstrategies for microgrids islanded operation,” IEEE Trans. Power Syst.,vol. 21, no. 2, pp. 916–924, May 2006.

• C. A. Baldan, J. S. Lamas, C. Y. Shigue, and E. R. Filho, “Fault currentlimiter using YBCO coated conductor-the limiting factor and its recoverytime,” IEEE Trans. Appl. Supercond., vol. 19, no. 3, pp. 1810–1813,Jun. 2009

THANK YOU…..