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Comparison of Two UV Imaging Parameterss Ln

the Insulator Fault DiagnosisLv Fang-cheng,Dai Ri-jun,Li Hai-de, Jin Hu

Hebei Provincial Key Laboratory of Power Transmission Equipment Security Defense, North China Electric PowerUniversity, Baoding 071003, China

Sande13142-@163.com

Abstract- At present, the main parameter is the ultravioletflare area and flare diameter, in order to has a contrast in

the insulator for fault diagnosis, in this paper, through the

water spray classification method to choice normal, good, a

mark, degradation and serious aging 5 kinds of insulation ofthe same kind of insulator. The platform structures is in the

laboratory, the pressurized are 8 kV, 10 kV and 15 kV,

through the South Africa CoroCAM504 UV camera to take

enough UV insulator pictures under discharge conditions,

using digital image processing algorithm extracting the two

parameters ,through MATLAB digital simulation, paper

obtain the change of two parameters with insulating of state

trend. The results show that: 1) when the insulator insulation

is in good condition, flare area and flare diameter almost

negligible, correspondence is better, conversely, in these two

parameters are small, it's always good insulator insulation. 2)

when the insulator insulation comes problems, both had a

tendency to rise, but flare area have a turning point 4, and

flare diameter not, this shows that when insulation

degradation to certain degree, flare area is not too big, anddifferentiate the spot diameter can be distinguished. Ultimately

it provides a quantitative assessment of the basis and certain

guidance for insulator in the running status .Key words- insulators; Ultraviolet imaging; light spot; Flare

diameter; Mathematical morphology; Condition assessment

I. INTRODUCTIONHigh voltage insulators bear high voltage level, during

the long-term operation process, for various reasons that theperformance of insulations will decrease, coincided with asurface discharge. According to its characteristics ofdischarge we can monitor its operation condition online,

detect the fault insulators and reduce the harm. UV imagingis a new method to detect insulation condition of high-voltage electrical insulators, the basic principle is that assessthe insulate situation of insulators by detecting the UV light

signals emitted from the discharge point of the insulatorssurface. Compared with the traditional detection methods,this method has characteristics of long detection distance,

non-contact, high sensitivity and positioning the dischargepoint precisely [1-3]. Currently, UV imaging method appliedin the power system mainly in the following aspects: (1)

Filthy discharge detection of high voltage electricalequipment; (2) Insulator discharge detection; (3)Externalinjury detection of wire; (4)Maintenance of high-voltagesubstation and line; (5) Find other sources of radio

interference[4]. However, in the current UV imaging methodquantitative and characterize the intensity of discharge isgenerally used the parameter of so-called flare number.But, according to the relevant information provided byequipment manufacturers we can see that the parameter isnot really the number of flare, just the number of spotswithin a period of time in the UV image area through theequipment used within a certain signal processing

algorithms. Flare number of parameters can be read directlyfrom the instrument screen, convenient and quickly. Butthrough extensive research and field pre-testing the authorsfound that the use of the actual number of ultraviolet flare to

characterize the discharge exist inadequate aspects: (1) flare

number and ultraviolet imagers gain, it appears morecomplex non-linear relationship in distance, and it isdifficult to get a better curve and not easy to quantify the

discharge; (2) flare number need to be read from the screenmanually, so it is not easy to extract and calculateautomatically, and so it is not easy to study the dynamicprocess of the discharge; (3) Observing distance have a

great impact on the number of flare, and the distance isdifficult to determine from the scene, under differentdistance testing results are not comparable.

During the observing, the scale of spot size (the area of

discharge and light-emitting region, this article will referredas spot )in the UV image change dynamic with thestrength of the discharge, this article will be defined as

spot area , compared with the flare number, the spot areahas the following characteristics: (1) The spot area extractedby the ultraviolet image in imaging method is actually theUV-channel images, that glow discharge and ionizationregion, the spot size and intensity of the discharge has a

more clear physical meaning; (2) The relationship betweenthe variation of spot size and gain of distance is better, andwe can get a clear explanation from works of imaging andinstrumentation, and this facilitate the engineeringapplications; (3) The use of image processing software can

2011 Second International Conference on Intelligent System Design and Engineering Application

978-0-7695-4608-7/11 $26.00 2011 IEEE

DOI 10.1109/ISdea.2011.173

1400

2012 International Conference on Intelligent Systems Design and Engineering Application

978-0-7695-4608-7/12 $26.00 2012 IEEE

DOI 10.1109/ISdea.2012.550

1400

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automatically calculate large number and continuous spot in

UV area of video, and the efficiency in parameter extractionis good. In the digital image, the discharge spot areacomposed by a lot of pixels. In the binary image each pixelin the region of1, while the black background region by

the 0. Therefore, the number of pixels of1"in statisticalimage matrix can be obtained by the number of spot area,

this article will be defined as spot area. The maximumdistance of two points in the edge of the spot is defined asspot diameter also stated by pixel value. At present, themore commonly used is these two parameters, but in thefield, in order to get better relationship corresponding withthe insulator failure, it is necessary to compare the

performance of these two parameters[4-5].

II. BUID TEST PLATFORMA. Test Selection

The main purpose of this paper is to compare the twoUV-fault diagnosis of parameters in the performance of

insulators. So choose a set of samples as follows: compositeinsulator, its model is FXBW4-10/70, a total of 5, theinsulating state as follows: by the method of waterclassification in the field select insulators in five kinds of

the insulating state: normal,well,micro marks,deteriorationand a serious of aging. Wash them before the test, then airdry for 24 hours, stand-by.

B. Test Process

Study will take place to ensure a stable power supply

and adjust spot size in the larger range as much as possible,so this paper uses ultraviolet imager model for South AfricaCoroCAM504, the use of video to record the test system

connection designed to test this section shown in Figure 1.

Fig.1 Experiment system connection diagram

The high voltage of high-frequency in test provided bythe HY-AC20-type 100kV of high voltage console,

composite insulators model is FXBW4-10/70. The front iscontrolled by the program, keeping gain the data thatremoved from a circular buffer, then send it into the bufferof application to compute, archive, and display graphics. As

long as the speed of data processing, archiving is larger than

the speed of data acquisition or equal to it, continuous data

collection will be sustainable.

III. THE CORRESPONDENCE BETWEEN SPOT AREA ANDTHE INSULATOR STATE

A. The Main Algorithm To Calculate Flare Area

Use computer technology to process image, translatethe images of JPEG format into BMP format, thats to saytransform the color images into grayscale pictures, andfurther into the gray-scale map of the binary pattern. Sothese pictures expressed by 0 and 1 , it is not only can

reduce the computer memory, the more important is theinformation of picture only have a relationship with theposition in the image of0 and 1, without consideringother factors , this is a great convenience to the scene. After

binarization, segmented discharge spot area by imagesegmentation techniques and digital image processing andmathematical morphology, further statistic thecharacteristics of spot. Binary image stored in a matrix

made up of0 and 1 , on which basis for mathematicaloperations, mathematical operation, and finally achieve thedischarge of quantification spot information, including flarearea and flare diameter. The two parameters provide an

important reference for the technical personnel.The mainly information Ultraviolet Imager get is

ultraviolet image. In order to get the information of onlineoperation insulator, need image processing, mainly using

image segmentation and morphologic image processing.Mathematical morphology is a kind of nonlinear analysismethods, which made signal waveform characteristicscompletely in the time domain. Image segmentation is a

typical example of its application, that is, to divide theimage into several meaningful area, extracted the image you

need to apply the feature, such as the pixel gray value,contour and texture of the object, and so on. Image

segmentation is the key steps of image processing for theimage analysis [6]. The basic approach: first choose a graythreshold in the image gray value range, and apply thethreshold to all image pixels. Because, usually, the whole

picture with a threshold to handle cannot get goodsegmentation results. So when using dynamic thresholdsegmentation method for software design, by adjusting thethreshold value, trial and error, until transfer to the

satisfaction of the outcome. The basic idea can berepresented by the following function:

1

1 2

2

0,

( ) 255,

0,

x T

f x T x T

x T

d-

t

(1)

Among them, 1T and 2T for the threshold.

Another image processing methods is mathematicalmorphology, including image erosion, expansion, image onor image closed operations. Corrosion of the operator is

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defined as .For a given image B and structure element

S, all the B has a related structure elements S, currentposition pixel is called S that is the collection of the B

corrosion.Mathematical expression of the operation is:

{( , ) }xyE B S x y S B (2)

Expansion can be expressed as:

( , ){( , ) [( ) ]}x yD B S x y S B z (3)

Where, for the expansion operator.

Image sharpening is to keep edge blur and contour

lines of the image becomes clearly, to clarify the detailsbetter. From a mathematical point of view, image fuzzy isthe essence of the image under the influence of average orsharing operations, therefore its inverse operation (such as

differential operations) can make the image clearer. Whileedge that detected by morphological edge detectionmethods is more smoother, retains more edge detail [7-8].This article uses second-order differential operator

Laplacian image enhancement. Continuous binaryfunction ,f x y , the Laplace operations defined as:

2 22

2 2

f ff

x y

w w

w w

For digital image, Laplace operator can be simplified as:

, , ,k l

r k s l

g i j f i r j s H r s

(4)

where , 0,1, 2, , 1i j N .

1, 1, ,k l H r s as follows:

1

0 1 01 4 1

0 1 0

H

(5)

B.Relationship of Spot Size And Insulation Condition

Test images are as follows:

Fig.2 Discharge experiment figure

Under the condition of the pressurized respectively for 8

kV, 10 kV and 15 kV, the measurement of flare area with

the changes of the insulation states are shown below:

Fig.3 The change of flare area with insulation state

IV.SPOT DIAMETER AND INSULATORS INSULATING STATEMAP

In this article, spot diameter and spot area for the samealgorithm, in the same case, are the following parameters:

Tab.1 The change of flare diameter with insulation state situation

Insulator

state

normal good Micro-

mark

degradation Serious

aging

Flare area

8

3 11 122 266 385

Flare area

10

4 13 135 275 392

Flare area

15

6 17 150 283 402

By MATLAB simulation, can get the following rules:

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Fig.4 Flare diameter with insulation change status curve

V. ANALYSISA. Spot size variation with the insulating state

(1) see from a single curve trend, before the "2" when the

insulation is in good insulator the spot size is almostnegligible, but curves rise rapidly between the "2" to "4" ,and after the "4 "although a certain rise, but more gentle.

(2) Between each curve, before the "2" almost overlap,after the "2", the curve of applied higher voltage slightly

higher than the curve of applied lower voltage.

B. Spot diameter variation with insulation status

(1) See from a single curve, before the "2" the rise isvery gentle, after the "2" rise rapidly, and there is no

turning point.(2) Although the three curves show the distribution with

the applied voltage level, but separation is not obvious.

C. Comparative Analysis

By 4.1 and 4.2, we may see:(1) When the insulation in good condition, spot area

and spot diameter is almost negligible, the correspondence

is better, on the contrary, when these two parameters aresmall, shows a good insulator insulation.

(2)When insulator insulation have problems, both areon the increase, but the spot area have a turning point "4",but did not spot diameter, which shows that, when the

insulation deterioration to a certain extent, the spot size isnot much distinction between degrees, while the spotdiameter can be distinguished.

VI. CONCLUSIONThrough the experiment, the article compared the

ultraviolet flare area and flare diameter with the changes ofthe insulation states insulator, analyses their characteristics,in general, made the following results:

(1) Design of test platform, South Africa CoroCAM504

Ultraviolet Imager, with 5 kinds of insulation condition ofan insulator by UV test under different voltage, received thetest pictures.

(2) Using mathematical morphology to process UV

image, and got different test conditions of ultraviolet flarearea and flare diameter.

(3) Obtain the changing relationship of the spot area andspot diameter with the insulating state through MATLABsimulation curve, and obtain each of their changes, andfinally, by comparing the two parameters change with theinsulating state, get the similarities and differences betweenthe two and ultimately achieve important quantitative basis

to assess insulator state.

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