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Optimal Positioning of Superconducting Fault Current Limiters for the Smart Grid Application Using Simulink On Project Report
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ABSTRACT
In this paper, an application of superconducting fault current limiter (SFCL) is proposed to limit the fault
current that occurs in power system, SFCL is a device that uses superconductors to instantaneously limit or reduce
unanticipated electrical surges that may occur on utility distribution and transmission networks. At the time of fault occurs
in the line, a large surge of power can be sent through the grid resulting in a fault. These faults can result in damage to
expensive grid connected devices. SFCL's eliminate or greatly reduce the financial burden on the utilities by reducing the
wear on circuit breakers and protecting other expensive equipment. Utilities can reduce or eliminate the cost of circuit
breakers and fuses by installing SFCL. As for a dispersed energy source, 10 MVA wind farm with three units connected
and the total was simulated. Three phase faults have been simulated at different locations in smart grid and the effect of the
SFCL and its location on the wind farm fault current was evaluated. Three wind farms were considered and their
performance is also evaluated. Consequently, the optimum arrangement of the SFCL location in Smart Grid with renewable
resources has been proposed and its remarkable performance has been suggested.
INTRODUCTION
Smart grid is a term used for future power grid whichintegrates the modern communication technology andrenewable
energy resources for the 21 st century powergrid in order to supply electric power which is cleaner,reliable, effervescent
and responsive than conventionalpower systems. Smart grid is based on the principle ofdecentralization of the power grid
network into smallergrids (microgrids) having distributed generation sources(DO) connected with them, One critical
problem due tothese integrations is excessive increase in fault currentdue to the presence of DO within a micro grid
[1],Conventional protection devices installed for protectionof excessive fault current in power systems,mostly at the high
voltage substation level circuit breakers tripped by over-current protection relaywhich has a response-time delay resulting
in powersystem to pass initial peaks of fault current [2].But, SFCL is a novel technology which has thecapability to quench
fault currents instantly as soon asfault current exceeds SFCL's current limiting thresholdlevel [3]. SFCL achieves this
function by losing itssuperconductivity and generating impedance in thecircuit. SFCL does not only suppress the
amplitudes offault currents but also enhance the transient stability ofpower system [4].Up to now, there were some research
activitiesdiscussing the fault current issues of smart grid [5], [6].But the applicability of SFCLs into micro grids was
notfound yet. Hence, in order to solve the problem ofincreasing fault current in power systems havingmultiple micro grids
by using SFCL technology is themain concern of this work.The utilization of SFCL in power system provide the
mosteffective way to limit the fault current and results inconsiderable saving from not having to utilize high capacitycircuit
breakers.
SIMULATION SET-UP
Matlab/Simulink/SimPowerSystem was selected to design and implement the SFCL model. Simulink/SimpowerSystem has
number of advantages over its contemporary simulation software (like EMTP, PSPICE) due to its open architecture, a
powerful graphical user interface (GUI) and versatile analysis and graphics tools. Control systems designed in the
Matlab/Simulink can be directly integrated with SimPowerSystemmodels. A complete smart grid power network including
generation, transmission, and distribution with wind farm model was also implemented in it.
Design of Power System
Newly developed micro grid model was designed by integrating a 10 MVA wind farm with the distribution network.Two
more wind farms are connected with the power system model for the analysis of power system connected with multi energy
sources. The power system is composed of a 100 MVA conventional plant, connected through 3-phase synchronous
machine which is connectedwith 200 km long 154 kV distributed-parameters transmissionline through a step-up
transformer TR1. At the substation(TR2), voltage is stepped down from 154 kVto 22.9 kV.High power industrial load (6
MW) and low power domesticloads (1 MW each) are being supplied by separate distribution networks. The wind farm is
directly connected withthe branch (B1) through transformer TR3 and is providingpower to the domestic loads connected to
the distributing line. The 10 MVA wind farm iscombination of five fixed-speed induction-type wind turbines eachhaving a
rating of 2MVA. At the time of fault, the domestic loadis being provided with 3 MVA out of which 2.7 MVA is provided
by the wind farm.Four prospective locations for SFCL installation are marked like Location 1 as Substation, Location 2 as
Branch Network, and Location3 as Wind farm integration point with the grid and Location4 as Wind Farm. Generally,
conventional fault current protectiondevices are located in Location 1 and Location 2.The output current of wind farm the
output of Transformer3 in Fig. 1 for various FCL locations have been measured and analyzed inSection III for determining
the optimum location of SFCL in amicro grid.
SIMULATION RESULTS
Three scenarios of SFCL’s possible locations were analyzedfor four different fault occurring points and no fault in the
power system depictedin Fig. 1. As per the first assumtion the single SFCL was locatedat Location 1 Substation. Second,
single SFCL was located atLocation 2 Branch Network. Third, single SFCL was locatedat Location 3 Wind farm
integration point with the grid
Fault in the Distribution Grid (Fault 1)
In the case of SFCL located at Location 1 Substation orLocation 2 Branch Network.Fault current contribution fromthe wind
farm was increased and the magnitude of fault currentis higher than No SFCL situation. These critical observationsimply
that the installation of SFCL in Location 1 and Location 2, instead of reducing itincreased the DG fault current. Thissudden
rise of fault current from the wind farm is caused by the abrupt change of power system’s impedance. The SFCLat these
locations (Location 1 or Location 2) entered into currentlimiting mode and reduced fault current coming from
theconventional power plant due to rapid increase in its resistance.Therefore the wind farm which is other power source and
alsocloser to the Fault 1 is now forced to supply larger fault currentto fault point (Fault 1).In the case when SFCL is
installed at the integration pointof wind farm with the distribution grid, marked as Location 3 in Fig. 1, fault current in
thewind farm has been successfully reduced. SFCLgives 68% reduction of fault current from wind farm and alsoreduce the
fault current coming from conventional power plantbecause SFCL is located in the direct path of any fault currentflowing
towards Fault 1.
With dual SFCL installed at Location 1 and Location 4,45% reduction in fault current is observed.Eventhough two SFCLs
were installed, fault currentreduction of wind farm is lower than what was achieved by the single SFCLinstalled at Location
3. By observing the simulation results it
Fault in Customer Grid (Fault 2)
Fig. 5 shows a comparison between fault current from thewind farm (measured at output of TR3) for differentSFCL
locations in the case when a three-phase-to-ground faultwas initiated in the customer grid Fault 2 in Fig. 1.Fault 2 is
comparatively a small fault as it occurred in lowvoltage customer side distribution network. The results observedare similar
to what were observed in the case of distribution grid(Fault 1) as explained in Section III-A.Once again the best results are
obtained when a single SFCLis located at Loc 3 which is the integration point of thewind farm with the distribution grid.
Fault in Transmission Line (F3)
The Fault 3 in Fig. 1 indicates the rarely occurring transmissionline fault which results in very large fault currents. Fig. 6
showsa comparison between fault current from the wind farm (measuredat output of TR3 in Fig. 1) for different Super
conducting fault current limiter (SFCL) locations inthe case when a three-phase-to-ground fault was initiated in
thetransmission line (Fault 3 in Fig. 1).When a fault occurs in transmission line, fault current fromthe conventional power
plant as well as the wind farm wouldflow towards fault point. For the wind farm condition, fault currentwould flow in
reverse direction through the substation and intothe transmission line to fault . Thus, on the contrary to theprevious results
obtained in Sections IIIA and IIIB, SFCL positionedat Location 1(Substation) or Location 2 (Branch Network)reduces the
fault current in wind farm. This result comesfrom the fact that SFCL is installed directly in the path of reversecurrent being
generated by the wind farm towards faultpoint.