Fault Detection and Classification in Transmission Line Based on Wavelets

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Relative Probability of Occurrence of Faults in Transmission Lines

Type of Short Circuit Fault

Percentage Occurrence

Single line to Ground (L-G)

70

Line to Line (L-L)

15

Double Line to Ground (L-L-G)

10

Three Phase Short Circuit (L-L-L)

2 or 3

SIMULATION MODEL FOR TRANSMISSION LINE FAULT ANALYSIS

A 3 phase transmission line rated 400kV and length of line is 300km has been considered for the case study. The circuit diagram of the transmission line fault analysis is shown in figure.

[pic 1]

Fig: Circuit for Transmission line Fault Analysis

Sequence Parameters of Source and Line

Source parameters

(Impedance Ω)

Positive, negative sequence

0.45+j5

Zero sequence

0.675+j7.5

Line Inductance

(mH/km)

Positive, negative sequence

0.95

Zero sequence

3.25

Line capacitance

(μF/km)

Positive, negative sequence

0.0124

Zero sequence

0.0084

Line resistance

(Ω/km)

Positive, negative sequence

0.0234

Zero sequence

0.3885

The fault analysis of transmission lines involves transient phenomena. Therefore, the positive, negative and zero sequence parameters of the source as well as transmission lines are necessary. The various line parameters pertaining to source as well as transmission line are shown in above table.

An active load of 500MW and a reactive load of 20MVAR (inductive) are used for the analysis.

[pic 2]

Fig: Simulink Model for Transmission line Fault analysis

The simulation model for the transmission line fed from one end is based on MATLAB and SIMULINK, as shown in figure 2.2. In the simulation model the first block represents a three phase equivalent source of 500MVA and 400KV. The next block (mutual inductance Z1-Z0) represents the positive, negative and zero sequence impedances for the source. The block for voltage and current measurement captures all the voltages as well as currents during the simulation. The two blocks representing transmission line are based on distributed parameter representation. Between the two transmission line blocks, (3 phase fault block) any particular type of fault is created. This block provides fault inception angle and fault resistance for any kind of faults. The last block represents a 3 phase load consisting of resistance and inductance.

FAULTED CURRENT WAVE FORMS

Factors affecting the fault current

The fault may appear at any instant of time, and thus voltage or current ranging from 0 to 360 degrees. The angle at which fault occurs is called fault inception angle and it effects the amplitude of fault current. The fault distance changes then corresponding line impedance changes which is going change the fault current. Fault resistance also affects the fault current. Fault resistance increases fault current decreases. Different types of power system faults are created using simulation model as shown, at different fault distances having different fault inception angles with different fault resistance. The wave forms are shown below.

[pic 3]

Fig: Ia, Ib, Ic for AG Fault at D==100Km, FIA=0, Rf=0.001Ω

[pic 4]

Fig : Ia, Ib, Ic for AB Fault at D==200Km, FIA=0, Rf=0.001Ω

[pic 5]

Fig: Ia, Ib, Ic for ABG Fault at D==200Km, FIA=0, Rf=1Ω

[pic 6]

Fig: Ia, Ib, Ic for ABC Fault at D==100Km, FIA=0, Rf=0.001Ω

FAULT DETECTION AND CLASSIFICATION

Wavelet Transform

The fault current signals are non-stationary in nature. Therefore, conventional Fourier transform and short time Fourier transforms are inadequate to deal with such signals. The Wavelet theory and its applications are rapidly developing fields in applied mathematics and signal analysis. The wavelet transform is a tool that divides up data into different frequency components, and then evaluates each component with a resolution matched to its scale. The wavelet transform is useful in analyzing the transient phenomena associated with transmission-line faults and/or switching operations. Wavelet analysis is the breaking up of a signal into shifted and scaled version of the original (or mother) wavelet. Scaling a wavelet means stretching (or compressing) it. Shifting a wavelet simply means delaying its onset.

Standard wavelets

Haar

Any discussion of wavelets begins with Haar wavelet which is the first and simplest. Haar wavelet is discontinuous and resembles a step function. It represents the same wavelet as Daubechies Db1.

Daubechies

Daubechies, one of the brightest stars in the world of wavelet research, invented what