CLASSIFICATION OF DIFFERENT FAULTS IN STATOR OF AN ALTERNATOR

8/11/2019 CLASSIFICATION OF DIFFERENT FAULTS IN STATOR OF AN ALTERNATOR

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IEJRD Journal of Science & Technology

E-ISSN: 2349-0721

Volume :1 Issue 1

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CLASSIFICATION OF DIFFERENT FAULTS IN STATOR OF AN ALTERNATOR

Manoj U. Bobade1, Prof.Niermal Chhajed

2,Prof. Pooja Ambatkar

3,Prof.Sneha Palkar

4

[email protected],[email protected],[email protected],

[email protected]

1Dept. of Electrical Engineering ,2Asst.Prof. Dept.Of Electrical Engineering,3Asst. Prof. Dept. Of ENTC, 4Asst. Prof. Dept. Of ENTC, AVBIT, Wardha

___________________________________________________________________________________________

Abstract:

Synchr onous generator are important elements of power system. Its reli abil ity and proper functioning are

crucial in maintaining an uninterrupted power supply to the customers. Their reliabil ity af fects the electri c energy

availabil ity of the suppli ed area. Hence the alternator pr otection is cri tical issue in power system as issue lies in the

accurate and rapid discrim inati on of healthy conditi on fr om diff erent faul ts. I t is very dif fi cult to describe the

relationship of f ault inf ormation and terminal parameters by accurate mathemati cal expression. By applying

arti fi cial neural network i n alternator, the fault diagnosis can obtain a good result. When there are faulty samples

in the traini ng samples of ANN, the severi ty inf ormation of the alternator faults can be directly obtained. Thi s

project describes a novel and simple arti fi cial neural networks (ANNs) technique without using r igorous

mathematics. I n th is project various faults were conducted on an laboratory al ternator and f ault curr ents were

captured using Data Acquisiti on System. The energies of these curr ent samples were calcul ated using Di screte

Wavelet Tr ansform and were given as input to ANN. The resul ts so obtained are f inall y compared to classif y the

faults.

Keywords: alternator, cur rent, ar tif icial neural network, data acquisition system, discrete wavelet tr ansform.

Introduction

Power system are the largest and most complex human made system, where faults always occurred. Faults can

reason workforce and tools safety problem, and can result in substantial financial fatalities. In classify to resolve the

problems, faults automatic detection, location and isolation must be employed. Most fault can cause large currents or

voltage changing, and they are often detected by traditional protective relay. Whereas, some faults such as high

impedance error, grounding error of unsuccessfully earthed distribution system, cause small currents and voltages

changing and they are difficult to be detected using traditional protective relay. Synchronous generators are important

elements of a power system. Its reliability and proper functioning are crucial in maintaining an uninterrupted power

supply to the customers. Some of important fault which may occur on Alternator are Overvoltage, Over speed, Over

current, Failure of Prime mover, Unbalanced Loading, Failure of Field and Stator winding faults (which includes Line

to earth Faults, stroke To stroke Faults, dual Line To Ground Fault, Three phase Fault and inter turn Fault.)
mailto:[email protected],[email protected],[email protected]:[email protected],[email protected],[email protected]:[email protected],[email protected],[email protected]:[email protected],[email protected],[email protected]:[email protected],[email protected],[email protected]:[email protected],[email protected],[email protected]:[email protected],[email protected],[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected],[email protected],[email protected]


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A lot of attention has been focused on generators single phase to ground fault which is one of the main causes

for shutting down a generator. . Stators winding fault must be avoided since the amount of time wasted and the cost for

repairing a generator is enormous. Hence, it is necessary to prevent such occurrences by incorporation reliable

protection and monitoring schemes.The Literature based on the algorithm which detects and discriminate the faults on

the basis of magnitude and direction of the reactive power. More recently two ANN based differential protectionscheme have also been introduce to provide protection for generator stator windings. While the first technique uses

samples taken from the line-side, neutral-end and field current of the generator, the difference and average of the

current entering and leaving the generator windings. This project describes the simple technique based on Artificial

Neural Network to discriminate various types of faults in Alternator. Three phase current of Alternator for normal and

faulty condition are captured with the help of data acquisition systems. (DSO) with 100MHz bandwidth an adjustable

sampling rate of 1GHz is used to capture the current. These currents are then fed as input to Artificial Neural Network

which then discriminate healthy and faulty condition.

Alternator:

A.Basic of alternator.

A.C. generators or alternators operate on the same fundamental principles of electromagnetic induction as D.C.

generators.

B.Principle of operation.

Alternators generate electricity by the same principle as DC producer. while magnetic field

lines cut across a conductor, a current is induced in the performer. In broad, an alternator has

a stationary part (stator) and a rotating part (rotor). The stator contains windings of conductors

and the rotor contains a moving magnetic pasture. The pasture cuts across the conductors, generating an electrical

current, as the mechanical input causes the rotor to turn.The rotating magnetic field induces an AC voltage in the stator

winding. Often there are three sets of stator winding, physically offset so that the rotating magnetic field produces athree phase current, displaced by one-third of period with respect to each other.

The rotor magnetic field may be produced by induction (in a "brushless" generator), by permanent magnets, or by

a rotor winding energized with direct current through slip rings and brushes. Automotive alternators invariably use

brushes and slip rings, which allows control of the alternator generated voltage by varying the current in the rotor field

winding. Permanent magnet machines avoid the loss due to magnetizing current in the rotor but are restricted in size
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owing to the cost of the magnet material. Since the permanent magnet field is constant, the terminal voltage varies

directly with the speed of the generator. Brushless AC generators are usually larger machines than those used in

automotive applications.

An automatic voltage control device controls the field current to keep output current constant. If the output voltage

from the stationary armature coils drops due to increase in demand more current is fed into the rotating field coils

through the automatic voltage regulator or AVR. This increase magnetic field around the field coils which induces a

greater voltage in the armature coils. Thus, the output voltage is brought back up to its original value.

Alternator in central power stations use may also control the field current to regulate reactive power and to help

stabilize the power system against the effect of momentary faults.

Faults

Definition:A fault in a line is any failure which interferes with the normal flow of current in the line. Most of

the fault on the power system lead to a short-circuit condition. When such a condition occurs a heavy current(short

circuit current) flows through the equipment, causing considerable damage to equipment and interruption of service to

the consumer.

3.2 Faults - Types and their Effects

It is not practical to design and build electrical equipment or networks so as to completely eliminate the

possibility of failure in service. It is therefore an everyday fact of life that different types of faults occur on electrical

systems, however infrequently, and at random locations. Faults can be broadly classified into two main areas which

have been designated Active and Passive.

Active Faults

The Active fault is when actual current flows from one phase conductor to another (phase -to-phase) or

alternatively from one phase conductor to earth (phase-to-earth). This type of fault can also be further classified into

two areas, namely the solid fault and the incipient fault.The solid fault occurs as a result of an immediate complete

breakdown of insulation as would happen if, say, a pick struck an underground cable, bridging conductors etc. or the

cable was dug up by a bulldozer. In mining, a rock fall could crush a cable as would a shuttle car. In these circumstances

the fault current would be very high, resulting in an electrical explosion.

This type of fault must be cleared as quickly as possible, otherwise there will be:

1. Greatly increased damage at the fault location.(Fault energy = 1 x Rf x t where t is time).

2. Danger to operating personnel (Flash products).

3. Danger of igniting combustible gas such as methane in hazardous areas giving rise to a disaster of horrendous

proportions.

4. Increased probability of earth faults spreading to other phases.


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5. Higher mechanical and thermal stressing of all items of plant carrying the current fault. (Xmers whose windings

suffer progressive and cumulative deterioration because of enormous electromechanical forces caused by

multiphase faults proportional to the current squared).

6. Sustained voltage dips resulting in motor (and generator) instability leading to extensive shut-down at the plant

concerned and possibly other nearby plants.

The incipient fault, on the other hand, is a fault that starts from very small beginnings, from say some partial

discharge (excessive electronic activity often referred to as Corona) in a void in the insulation, increasing and

developing over an extended period, until such time as it burns away adjacent insulation, eventually running away and

developing into a solid fault.

Other causes can typically be a high-resistance joint or contact, alternatively pollution of insulators causing

tracking across their surface. Once tracking occurs, any surrounding air will ionize which then behaves like a solid

conductor consequently creating a solid fault.

Techniques For Classification Of Alternator Faults

The techniques for classification of alternator faults include:

A) Time domain analysis

B) Frequency domain analysis

C) Using Artificial Neural Network

Algorithm For Fault Discrimination Using Ann.

1.Start and run the alternator at its rated speed.

2.Faults are done on alternator with the help of contactor and take different types of fault reading.

3.The current signal captured with the help of DAS and the energies of these current signals are calculated using

DISCRETE WAVELET TRANSFORM and given as input to ANN

4.ANN get trained and classify the faults.

FLOWCHART


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EXPERIMENTAL CIRCUIT DAIGRAM

EXPERIMENTAL SETUP

Fig no:1 fig no:2.

Fig no:3

Specifications of ANN:1)Network used: multi-layer feed forward.2)No of Hidden layer(s) : 1. 3)Cross

validation : zero.

4)Test percentage : 50%. 5)Transfer function : tanhaxon.6)Learning rule : momentum.7)Maximum Epochs :

10008)Step size : 1.00. 9)Momentum : 0.7.Info about DWT:1)Mother Wavelet : db4.2) Decomposition

levels : 1 to 5. 3)Window type : rectangular window (i.e. rectwin).4)Number of section for each signal :

Results

A.Line-to-ground fault:When one line conductor comes in contact with ground, is said LG fault. It is most severe

fault when it is near to generator terminal.

Sr.no. Name of facilities specification

1 3ph Synchronous Generator 1KVA, 400V, 1.5A, 3000rpm

2 DC Shunt Motor 0.75hp,230V,6.8A,1500rpm

3 Ammeter 0-5 A

4 Rheostat 1750/0.6A

5 Rheostat 750/1.2A

6 Voltmeter 0-600V

7 DSO & CTs


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Fig:graphical representation of current Vs time for LG fault reading

Above figure represents the fault current wrt time. On x-axis time is present and on y-axis magnitude of current.

0 200 400 600 800 1000 12000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

X:144.1

Y:1.054

fft ofofIaLG

Fig:graphical representation of current Vs frequency for LG fault reading

current Vs frequency for LG fault reading graphical representation energies at five different levels for 14

differeent sets of readingsAbove figure shows energies of fault currents at five different levels as in wavelet transform

the energy is decomposed to five different energy levels.

A. Double Line-to-ground fault

When two line conductors comes in contact with ground is said to be LLG fault. It is unsymmetrical type of fault

0 500 1000 1500 2000 2500-50

050

Signal

WAVELET DECOMPOSITION OF SIGNAL

500 1000 1500 2000 2500-20020a

500 1000 1500 2000 2500-1-0.500.5d

500 1000 1500 2000 2500-0.4-0.200.20.4d

500 1000 1500 2000 2500-0.500.5d

500 1000 1500 2000 2500-101d

500 1000 1500 2000 2500-202d

Switching instant

of fault current

x=144.1

y=1.054

Switching instant offault currents


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Above figure represents the fault current wrt time. graphical representation of current Vs frequency for LL fault reading

On x-axis time is present and on y-axis magnitude of current. Above figure represents various frequency components present in fault current.

On x-axis frequency is present and on y-axis amplitude of current

Triple Line fault:

current Vs frequency for LL fault reading graphical representation of current Vs time for LLL fault readingAbove figure shows energies of fault currents at five different levels as When all line conductor get short then it is said to be LLL fault. This is most severe fault . This is

symmetrical fault.. in wavelet transform the energy is decomposed to five different energy levels.

ANN RESULTS: Using multilayer perceptron for one cycle and testing percentage 50%.

Fig: percentage accuracy Vs PE for one cycle.

Table shows the results of classification of various faults in an alternator by the use of 50% training percentage

and multilayer perceptron, it is found that the best results are obtained with 3 processing elements for one cycle.

Network description : 1) Number of hidden layer=1

2) Transfer function= tanhexon

3) Processing elements=8

4) Result obtained= 71%

0 50

100

150

200

250

-1

01

Signal

WAVELET DECOMPOSITION OFI

50

100

150

200

250

-

05a

50

100

150

200

250

-01d

50

100

150

200

250

-

01d

50

100

150

200

250

-0.

00.

d

50

100

150

200

250

-0.

-0.

00.

0.

d

50

100

150

200

250

-0.

-0.

00.

d

0 50 100 150 200 2500

0.

1

1.

2

2.

3

3.

X:

.

Y:.

fft of of

x=141.7

y=0.7152

Switching

instant of fault

currents


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Best suited network:

DISCUSSION ON RESULT:1)In artificial neural network multilayer percepton network is used.

2) In MLP no of processing elements used are 1 to 8 and percentage accuracy obtained for

LG,LLG, LL, LLL faults are 100% with 4 neurons and 50% testing percentage.

The above table gives the comparative results of time domain and frequency domain

(FFT and DWT ) and best results are obtained in frequency domain and mainly with

the help of discrete wavelet transform.

DISCUSSION ON RESULT:In artificial neural network multilayer perceptron network is used.In MLP no of processing elements used

are 1 to 8 and percentage accuracy obtained for LG,LLG, LL, LLL faults are 100% with 4 neurons and 50% testing percentage.

Conclusion Conclusion:This project describes a simple technique based on ANN to classify stator faults.

A neural N/W which consists of one hidden layer, one neuron, using multilayer perceptron for training with energy of d-level 1to4 as

inputs is found to be the best N/W.

Future Scope:This method is an offline method & can be made online by connecting some embedded system consisting of some

threshold weights to the experimental set up which is used to capture current waves & input can be given to ANN to classify the faults.

References

"Protective Relays Applications Guide," The English Electric Company Limited, Relay Division, Stafford,

1975.

C. J. Mozina, IEEE Tutorial on the Protection of Synchronous Generators, IEEE Tutorial Course, IEEE Power

Engineering Society Special Publ., no. 95 TP102, 1995.

M. S. Sachdev and D. W. Wind, "Generator differential protection using a hybrid computer," IEEE Trans.Power Apparatus System, PAS-92(1973) 2063-2072.

H. Tao and I. F. Morrison, "Digital winding protection for large generators," J. Electr. Electron. Eng. Aust., 3

(1983), 316-321.

Current Differential Protection of Alternator Stator Winding N.W.Kinhekar, Sangeeta Daingade, and

Ajayshree Kinhekar

Time DFT DWT

CLASSIFICATION OF DIFFERENT FAULTS IN STATOR OF AN ALTERNATOR

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