Fault Analysis in Four-wire Distributed Networks

8/3/2019 Fault Analysis in Four-wire Distributed Networks

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BY:

MD ABDUL RAHEMAN

UNDER THE GUIDENCE OF:

M N SUNEETHA

R.M. Ciric, L.F. Ochoa, A. Padilla-Feltrin and H. Nouri, Members, IEEE


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Fig. 1. Three-phase four-wire line section, considering ground.

where

a, b, c phase lines;

n neutral wire;g ground.

5x5 impedence matrix

POWER FLOW ALGORITHM


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A. Model

Fig. 2. Model of the three-phase four-wire multi-grounded distribution line.


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B. Power Flow Algorithm

At iteration k:

1. Nodal current calculation

WhereIia, Iib , Iic,Iin , Iig are the current injections at node i;

Sia, Sib, Sic, are scheduled (known) power injections at node i;

Via, Vib , Vic , VinVig are voltages at node i;

Yia Yib, YicYin, Yig admittances of all shunt elements at node i;

Zgri grounding impedance at node i ( Zgi = Zgri+ Zggi )


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2) Backward sweepsection current calculation

Where

current flows on line section ;

M set of line sections connected downstream to node j .


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3) Forward sweepnodal voltage calculation

. Voltage Correction:


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Convergence Criterion:

the power mismatches at each node for all phases, neutral wire, and ground arecalculated as

Flat Start:

The initial voltage for all nodes should be equal to theroot node voltage

If the real or imaginary part of any of the power mismatches is greater than a

convergence criterion, steps 1, 2, and 3 are repeated until convergence is achieved.


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SHORT-CIRCUIT ANALYSIS

The hybrid Thevenin equivalent is calculated from:

General fault boundary conditions in a 5x5 network representation for calculatingdifferent types of fault are given as:

Where

Vt is the voltage mismatch vector from (7)Vf

(s) is the scheduled voltage (fault boundary condition)

Vf(0) is the pre-fault voltage at the faulted node


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Thevenin compensation impedance matrix Zt is determined in the form of a3x3-network representation.

Hence, boundary fault conditions for Vf(s) are kept in 3x3 notation.

solving fault currents It by (7),

Node current injections of phases a, b and c = post-fault current injections + pre-faultnode current injections.

The pre-fault node current injections of phases a, b and c are determined frompower flow solution.


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For three-line-to-ground faults, at a three-phase line section, post-fault currentinjections are given by:

whereIfa

(p) , Ifb(p), Ifc

(p) are post-fault phase current injections

Ita, Itb, Itc are fault currents obtained by solving (7).

For double-line-to-ground faults or line-to-line faults, on phases b and c, post-

fault current injections can be If(p)

formed by


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For single-line-to-ground fault on phase a, post-fault current injection If(p) is

determined from

Post-fault node current injections of the neutral wire and ground are thencalculated using

where

Ifn(p)

, Ifg(p)

are post-fault neutral wire and ground current injectionsZgrfis the grounding impedance at the faulted node

Znnf, Zggfare neutral wire and fictitious ground conductor impedances in thefaulted section (Zgf=Zgrf+Zggf).


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CONCLUSION

In this paper a method for fault analysis in four-wire DNs is discussed.

In this paper, a power flow algorithm for three-phase four-wire radial DNs,considering neutral wire and multigrounding, is proposed.

High-order line models (4x4, 5x5 and higher) may easily be added to acommon solution method for three-phase power flow.

Documents

Fault Analysis in Four-wire Distributed Networks