An Algorithm Based On Discrete Wavelet Transform For Faults Detection, Location and Classification in Radial Distribution System

ISSN 2349-7815
International Journal of Recent Research in Electrical and Electronics Engineering (IJRREEE)
Vol. 2, Issue 2, pp: (41-47), Month: April 2015 - June 2015, Available at: www.paperpublications.org
Page | 41
Paper Publications
An Algorithm Based On Discrete Wavelet
Transform For Faults Detection, Location and
Classification in Radial Distribution System
1
Ranjitha H, 2
Mr. K. R. Mohan, 3
Mr. B. Kantharaj
1
PG Student, 2
Associate Professor and Head of the Department, 3
Associate Professor, Department of EEE,
Adichunchanagiri Institute of Technology, Chikmagalur
Abstract: An electric power distribution system is the final stage in the delivery of electric power; it carries
electricity from the transmission system to individual consumers. Fault classification and location is very
important in power system engineering in order to clear fault quickly and restore power supply as soon as possible
with minimum interruption. Hence, ensuring its efficient and reliable operation is an extremely important and
challenging task. With availability of inadequate system information, locating faults in a distribution system pose a
major challenge to the utility operators. In this paper, a faults detection, location and classification technique using
discrete wavelet multi-resolution approach for radial distribution systems are proposed. In this distribution
network, the current measurement at the substation have been utilized and is demonstrated on 9-bus distribution
system. Also in this work distribution system model was developed and simulated using power system block set of
MATLAB to obtain fault current waveforms. The waveforms were analyzed using the Discrete Wavelet
Transform (DWT) toolbox by selecting suitable wavelet family. It was estimated and achieved using Daubechies
‘db5’ discrete wavelet transform.
Keywords: Fault detection, Fault location, Fault classification, Multi-resolution analysis, Discrete wavelet
transform, Distribution system
I. INTRODUCTION
An important objective of all the power systems is to maintain a very high level of continuity of service, and when
abnormal conditions occur, to minimize the outage times. It is practically impossible to avoid effects of natural events,
physical accidents, failure of equipment or mis-operation which results in the loss of power, voltage dips on the power
system.
The very important issue in power system engineering is to locate the fault and estimate the distance in order to clear fault
quickly and restore power supply as soon as possible with minimum interruption.
Natural events can cause short circuits i.e. faults which can either be single phase to ground or phase to phase or phase
to phase to ground or a three phase fault. Most faults in an electrical system occur with a network of overhead lines are
single-phase to ground faults caused due to lightning induced transient high voltage and from falling trees. In the
overhead lines, tree contact caused by wind is a major cause for faults. The appropriate percentages of occurrences
various faults are listed below:
Single line to ground fault – 70-80%
Line-Line to ground fault - 10-17%
Line-Line fault – 8-10%
Three phase – 2-3%

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Paper Publications
Recently, several fault location methods for transmission and distribution system have been proposed. They are
categorized in three main categories;
1) Impedance based methods; these methods usually calculate the apparent impedance sequences using measurement
point data and estimate the possible fault locations based on iterative algorithms. Considering the multiple fault locations
estimation in these method and existence of many laterals in distribution system is the drawback of impedance base
methods.
2) Intelligent methods consist of artificial neural networks (ANN), expert systems and etc. ANN based method need to be
trained after any change in system and update network weights, the other drawback with ANN based methods is that in
case of complicated networks they became slow and may fall in local optimum. Expert system methods have a slow
response time since they involve knowledge based maintenance and conventional interference mechanism.
3) Wavelet transform; The wavelet transform (WT) is a recently developed mathematical tool which can be used for
signal processing with a wide variety of applications, e.g. acoustics, communications, transient analysis, medicine, etc.
The main reason for this growing activity is the ability of the wavelet not only to decompose a signal into its frequency
components, but also to provide a non-uniform division of the frequency domain, whereby it allows the decomposition of
a signal into different levels of resolution.
In general, the first step in the power system relaying algorithms is the detection of fault and the next step is
classification. This work uses a combination of Wavelet Transforms and multi-resolution detecting and classifying power
system faults. The Objective of this work is to classify the faults according to the following parameters:
1. Fault type
2. Fault location
The fault cases are classified as single phase to ground faults, phase to phase to ground faults and a three phase faults.
The fault location is an important parameter especially in high voltage power systems. The knowledge of fault location
leads to high speed fault clearance as well as improved transient stability.
II. HISTORICAL REVIEW: FROM FOURIER ANALYSIS TO WAVELET ANALYSIS
The history of wavelets begins with the development of the traditional Fourier Transform (FT), which is widely applied in
signal analysis and image processing. Fourier Transform breaks down a signal into the sum of infinite series of sines and
cosines of different frequencies. Fourier transform is very effective in problems dealing with frequency location.
However, time information is lost during the process of transforming to frequency domain.
To improve the performance of the FT, the Short Time Fourier Transform (STFT) has been developed in signal analysis.
STFT compromises between the time and frequency based views of a signal by examining a signal under a fixed time
window. The drawback of STFT is that , for all the frequencies the time window is fixed. Many signals require a more
flexible approach; the window size is required to vary according to the frequency.
Wavelet analysis or wavelet transform is close to the Fourier transform, but has a significant advance. It applies a
windowing technique with variable-sized regions, a shorter time interval is used to analyze the high frequency
components of a signal and a longer one is used to analyze the low frequency components of the signal. Wavelet analysis
is very effective for dealing with local aspects of a signal, like trends, breakdown points, and self similarity. Furthermore,
wavelet analysis is capable of removing noise from signal and compress signal.
III. DISCRETE WAVELET TRANSFORM (DWT) AND MULTI-RESOLUTION ANALYSIS
(MRA)
The wavelet transform is a mathematical tool that divides up data, functions or operators into different frequency
components and then studies each component with a resolution matched to its scale. Basically, wavelet transforms are
divided into two, namely: Continuous Wavelet Transform (CWT) and Discrete Wavelet Transform (DWT). Since most
operations are now performed using computers, which uses digital forms of data, the latter is preferred by most
researchers and is used in this study.

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The DWT analyses the original signal at different frequency bands with different resolutions by decomposing the signal
into a coarse approximation and detail information. In doing this, the DWT employs two sets of functions called Scaling
functions and Wavelet functions. These are respectively associated with high and low pass filters.
Fig.1 Schematic Diagram of Multi-Resolution
Analysis of DWT Decomposition
KEY
=Down Sampling by 2
LPF= Low Pass Filter
HPF= High Pass Filter
A=Approximation Co-efficient
D =Detail Co-efficient
A very useful implementation of DWT, called multi-resolution analysis, is demonstrated in Fig. 1. It is designed to
produce good time resolution and poor frequency resolution at high frequencies and good frequency resolution and poor
time resolution at low frequencies. The original sampled signal I(n) is passed through a high pass filter g(n) and a low
pass filter h(n). Then the outputs from both filters are decimated by 2to obtain the detail coefficients and the
approximation coefficients at level 1 (D1 andA1). The approximation coefficients are then sent to the second level to
repeat the procedure. Finally, the signal is decomposed at the expected level.
In the case shown in Fig.1, if the original sampling frequency is F, D1 captures the signal information between F/4 and
F/2 of the frequency band. D2 captures the signal between F/8 and F/4. D3 captures the information between F/16 and
F/8, and A3retains the rest of the information of original signal between 0 and F/16. By such means, we can easily extract
useful information from the original signal into different frequency bands and at the same time the information is matched
to the related time period. In this work db5 wavelet is used to make a 3 level decomposition. The wavelet tool box in
MATLAB provides a lot of useful techniques for wavelet analysis.

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IV. MATLAB SIMULATION
A simulation model is developed for the system shown in figure 2 using simulink.
Fig.2 Single line diagram of the 9-bus distribution system
Table I: Generator rating
Generators Ratings
Generating station 11KV, 50Hz
Table II: Distribution line data set
Sending End bus Receiving End Bus R (ohm) X (henry)
0 1 0.1233 0.4127
1 2 0.0140 0.6050
2 3 0.7463 1.2050
3 4 0.6984 0.6084
4 5 1.9831 1.7276
5 6 0.9053 0.7886
6 7 2.0552 1.1640
7 8 4.7953 2.7160
8 9 5.3434 3.0264
Table III: 9BUS data set
Bus No. Active Power (P) in KW Reactive Power (Q) in KVAR
1 1840 460
2 980 340
3 1790 446
4 1598 1840
5 1610 600
6 780 110
7 1150 60
8 980 130
9 1640 200

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A. The Phase Currents of the Simulation Model without Faul:
Fig.3 Healthy 3phase current signal
B. The Phase Currents of the Simulation Model with L-G Fault:
Fig.4 Current waveforms for an L-G fault
V. RESULTS AND DISCUSSION
A. Wavelet Distance Protection Algorithm:
In order to investigate the applicability of the proposed wavelet transform distance protection algorithm, a simulation of
distribution line model is developed. Fault simulations were carried out using MATLAB. The three phase current signals
are then filtered using the pre-band-pass filters to attenuate the dc component. The output filtered signals are the input to
the proposed wavelet distance protection algorithm.
B. Analysis of L-G Fault:
The simulated fault signals are being analyzed through the wavelet transform using MATLAB wavelet toolbox. Three
phase current signals are loaded to wavelet 1-D in the wavelet toolbox main menu. The proposed technique is divided
into two sections.
1) Fault Detection:
The first section is detection of the fault by observing the output of the high pass filter details of the first decomposition
level. This decomposition level has the ability to detect any disturbances in the original current waveform. The loaded
current signals are decomposed at one level with the db1 wavelet.

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Fig.5 First level decomposition of phase ‘a’
Fig.6 First level decomposition of phase ‘b’
Fig.7 First level decomposition of phase ‘c’
2) Estimation of Current:
The second section of the algorithm is the estimation of the fundamental frequency currents. It can be done by observing
the output of the low-pass filter at the third decomposition level (A3). The third level of decomposition gives good
approximation of the phasors. At this level the high frequencies in the signal are eliminated by the high-pass filters of the
first and second decomposition levels and DC component has already been eliminated by pre-band-pass filtering the
signal. The estimation of phasors is based on capturing the peak value of each signal (magnitude).The three phase current
signals are decomposed by the db5 wavelet.

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Fig.8 3-levels of decomposition of phase ‘a’
VI. CONCLUSION
In this paper, the wavelet Multi-Resolution Analysis (MRA) has been applied to identify and locate the fault in the radial
distribution system and is tested on 9-bus distribution system. This wavelet based technique allows decompose the signal
into frequency bands (multi-resolution) in both time and frequency allows accurate fault detection as well as estimation of
fault current signal at the fundamental frequency. The MRA approach is found to be very effective in identifying various
types of fault (LG, LL, LLG, and LLLG) and also in locating the faulty section. Hence, the method is quite simple to
adopt and extremely fast for the fault identification and location.
REFERENCES
[1] Mukesh Thakre, Suresh Kumar Gawre And Mrityunjay Kumar Mishra, “Distribution System Faults Location And
Classification Based On Wavelet Transform,” ISSN 2319-2526, Vol. 2, Issue-4, 2013.
[2] S.Mallat, “A theory for multi resolution signal decomposition: The Wavelet representation,” IEEE Trans. Pattern
Anal. Machine Intell , vol.11, pp. 674–693, July 1989.
[3] Ngaopitakkul, C. Apisit, C. Pothisarn, C. Jettanasen and S. Jaikhan, “Identification of Fault Locations in
Underground Distribution System using Discrete Wavelet Transform”, A vol.2, March 2010.
[4] U. D. Dwivedi, s. N. Singh, S. C. Srivastava, “A Wavelet Based Approach for Classification and Location of
Faults in Distribution Systems”, IEEE, 2008, pp.-1-6.
[5] Om Prakash Mahela, Sheeesh Ram Ola, Lalit Goyal, “Optimal Capacitor Placement for Loss Reduction in Radial
Distribution Feeder,” IOSR-JEEE, vol. 4, pp 43-48, April 2013.
[6] D. Prabhavathi, K. Prakasam, Dr. M. Suryakalavathi, Dr. B. Ravindranath Reddy, “Wavelet Based Detection and
Location of Faults in 400KV, 50km Underground Power Cables,” IJCER, vol.5, Feb. 2015.
[7] Subba Reddy .B, D. Sreenuvasalu Reddy, Dr. G.V. Marutheshwar, “ Identification of Fault Location in Multiple
Transmission Lines by Wavelet Transform,” IJCER, vol.4, Feb. 2014.

An Algorithm Based On Discrete Wavelet Transform For Faults Detection, Location and Classification in Radial Distribution System

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An Algorithm Based On Discrete Wavelet Transform For Faults Detection, Location and Classification in Radial Distribution System