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  $EM!N@R on

Electromagnetic Transient Analysis of

the Saturated Iron-Core

Suer conductor ault Current "imiter 

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OBJECTIVES:

 Superconducting fault current limiters offersuperior technical performance in comparison with

conventional methods to limit fault currents.

 Considering the actual structure, the sophisticated

equivalent magnetic circuit of the SISFCL was

proposed first in the paper.

 The electromagnetic transient simulation model of

the SISFCL was built in MatlabSimulin!.

 "ewton iteration method and fundamental

magnetic magneti#ation curve are introduced.

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I"T$%&'CTI%"(

  )igher electrical loads, new consumers, and newdistributed generation plants are constantl* being added.

 The concern is that the e+pected fault current levels ma*

e+ceed the interrupting capabilit* of the e+isting Cs.

  There are several traditional approaches to suppress the

fault current

 System reconfiguration .

 Bus splitting.

 Insertion of high impedance transformers or air-

core reactors.

 An alternative solution to the problem, whichhas gained much attention lately, is the

application of

  -Fault Current Limiter ,,

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Comarision #ith SISC"

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n FCL is t*picall* installed in series with theequipment to be protected.

'nder normal operating conditions, the FCL

displa*s negligible impedance so that the powerflow is unobstructed.

In the event of a fault, however, the FCL/s

impedance rapidl* increases, which limits the

fault current.

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CLASSIFICATION:

Base upon the task performed,

a. un0interrupting t*pe .

b. interrupting t*pe.

c. Composite t*pe.

FCLs can be implemented with passive non0linear

elements, inductive devices, vacuum switches ,semi conductor switches, superconductors.

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DESIRED FEATURES

In the normal state the FCL is expected to:

a1have a low insertion impedance2

b1be able to withstand distribution and transmission level

voltage and current ratings2

c1have a low voltage drop2

In case of a fault, the FCL is required to:

a1be capable of limiting the first fault current pea!2

b1displa* a large increase of impedance2

c13ithstand the fault condition for a sufficient time

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ST'$T4& I$%"0C%$4

S'54$C%"&'CTI"6 F'LT C'$$4"T

LIMIT4$ .

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WORKING OF SISFCL

  In normal operation mode,

 The dc current in superconducting coil drives both

iron cores into deep saturation.

 As the low permeability of saturation region, the

inductance of SISFCL is very small in normaloperation condition.

 In a fault operating mode,

The high ac current drives the wor!ing points of two iron cores

to be out of saturation alternatel* each half c*cle.Since the permeabilit* of the cores increases significantl*, a high

impedance value is obtained to limit the fault current .

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EQUIVALENT MAGNETIC

CIRCUIT

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 According to the law of magnetic circuits,

 Hs1ls+ H y1l y + Hc1lc= Naciac + Ndcidc =F1  (1)

 Hs1ls+ H y2l y + Hc2lc = Naciac − Ndcidc =F 2 (2)

 According to the equivalence principle, the equivalent

excitation , currents of the two iron cores are satisfied

with

  Naciac + Ndcidc =Ndciμ1 (3)

  Naciac − Ndcidc =Ndciμ2  (4)

The current-limiting inductances Lμ is given by

  Lμ=Lμ1+Lμ2=(Ls1 //L y1 //Lc1 ) + (Ls2 //L y2 //Lc2 ) (5)

 By combining all these eq.the magnetic flux ΦC1 and ΦC2 

 passthrough the iron coresC1 and C 2 , shown in Fig. 1.is

 given by….

  N 2dcc1(1/Lμ1 )= Naciac + Ndcidc = F1  (6)

  N 2dcc2(1/L μ2 )= Naciac − Ndcidc =F 2  (7)

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"ewton iteration methodis used in this paper to solve

nonlinear computation

  since the magnetic flux is an unknown

quantity , e q .(6) and (7) can be transformed into

  f() = 0 (8)

The correction equation of newton iteration

method is

f((k)) + f ’((k))∆(k) = 0 (9)

 For k+1 step,(k+1)=(k)+ ∆(k) =(k) – f((k) ) / f ’((k) ) (10)

The iteration calculation will not stop until the following condition is satisfied…

 

max fi((k+1 ) ) < €

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lgorithm process

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E%ECTE& RES'"T

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MM AN& "' ( T)( IR(N C(RES

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