C Pollution measurement based on DDG method for different type s of insulator profile

Transcription

1 21, rue d'artois, F Paris C4-401 Session 2004 CIGRÉ Pollution measurement based on DDG method for different type s of insulator profile M.R.Shariati *, A.R.Moradian, M.R.Ghaemi, M.Oskouee A.Omidvarinia B.Masoudi Niroo Research Institute (N.R.I) Khuzestan D.E.C TAVANIR IRAN Abstract Iranian southern provinces are one of the severe environmental conditions based on DIN and its large temperature fluctuations and condensation phenomenon, resulting in dew, worsens the situation for T&D network. In order to overcome these conditions and determining insulator maintenance intervals, we measured site pollution severity by ESDD and NSDD parameters at 3-monthly periods. We installed an online leakage current monitoring system for evaluating of leakage current of polluted insulators in daily & monthly periods. Another method for measuring of pollution in parallel of mentioned methods was DDG that helped us to develop a simple and passive method for measuring pollution in the other areas. Measuring of ESDD and NSDD on 5 types of insulators and comparing of the result with LCM and DDG methods shows we can define a Correction factor based on profile of insulator for measuring of site severity on DDG method, so in this paper we introduce a correction factor based on profile of insulator. Keywords Insulator Directional Dust Gauge -Site Pollution Severity ESDD-NSDD - Leakage Current 1-Introduction Iran s location in middle east with its variety of climate including little rain, frequent sand storms, condensation phenomenon and dew resulting from large temperature fluctuations between day & night worsen the situation for T&D system, particularly in regions close to Persian Gulf & Oman sea. Site severity with respect to pollution often affects the dielectric performance and reliability of stations & HV lines. Pollution monitoring becomes therefore, more and more important and needed for the proper design and choice of insulation, establishment of adequate maintenance procedure and defining effective countermeasures against pollution s flashovers. Up to now, several investigations has been done to classify the contamination location and its degree around the world. In order to assess the pollution severity of a site in addition to interpretation and application of the test results, a procedure seems to be necessary. Among many useful procedures DDG was chosen, * mshariati@nri.ac.ir

2 because it requires no power supply, it is inexpensive and simple enough to be applied by local personnel. Considering the mentioned severe climate in Iran, N.R.I (Niroo Research Institute) now has more than 270 test insulators installed on 30 de-energized ESDD stations and 30 DDG test-stations in addition to an energized test-station equipped with LCM system through out the state of Khuzestan in Iran. In this research the behavior of different types of insulators, with different shapes, under natural condition dominated by mixed marine, industrial and desert pollutions are assessed.in addition, through a comparative field study at several sites, practical results and information on application of the resulted data from pollutions monitoring methods (ESDD-NSDD, LCM and DDG methods) are presented. 2-Experimental Methods 2-1-ESDD, NSDD Method The contaminants were removed with a cotton swab and carefully collected from area of the test specimens, except the metal parts. The contaminants were dissolved in de-ionized water and stirred; then the conductivity was measured by a volume conductivity meter and corrected to room temperature (20 C) by a correction factor. The salinity of the solution was determined and ESDD was estimated from the volume of the solution, area of the clean surface and the salinity. Afterwards a pre-dried and weighted funnel should filter out the solution; filter paper will be weighted again. NSDD shall be calculated based on IEC & This procedure is time consuming but it has the capability of assessing the self-cleaning properties Test sites And Specimen Insulators Thirty stations were established to investigate insulators behavior and pollution severity. Each station contains an insulator string of five cap & pin discs, a pin type insulator (ANSI (56-3)), a pin type insulator (ANSI (56-5)), a long rod insulator, and a pedestal insulator supported on a concrete or wood pole structure. ESDD and DDG Test stations were located in heavy industrial and marine polluted areas of Khuzestan, a southern state in Iran, as shown in figure 1. The mentioned specimens are shown in figure 2 and their characteristics are presented in table 1. ESDD Station 3 DDG Stations Fig. 1: Exposure Test Stations 2

3 2-2-Leakage Current Monitoring Leakage current monitoring was performed on cap and pin insulators (No: 1-5). The insulators were mounted in a vertical position at the same height as those used for the ESDD measurements. The system consist of a sensor, protective system, data transfer system, Personal Computer and accessories. Main programs written in the lab view package were used for storing LC data and their analyses. In this method, the highest peak current of an energized insulator at its service voltage is recorded in a certain period. Recent studies have shown that an arc of minimum length must be established before flashover can occur. A critical current, which has been expressed with formula (1), is associated with this critical arc length. 2 ^ 800X c Ic = (1) ^ V c Where : X c =critical arc length [ cm ] ^ V c =Flashover voltage [ Volt] Pederson [7] substituted X c by 2L/3, where L is the insulator creepage path length, and obtained good correlation between calculated and measured values of the critical current. It was confirmed by practical measurement, that: ^ 1600L Ic = ^ 3V c (2) Therefore: ^ 2 I c = KS (3) Where : K= , S= the specific creepage distance [ mm/kv ]Um Table 1: Characteristics of Tested Insulators Leakage Path Insulator Type Designation No. (mm) 2 Shed diameter (mm) Cap-and-Pin Pedestal Pin Type ANSI (56-3) Pin Type ANSI (56-5) Long Rod Directional Dust Gauges Four dust gauges, each gauge sets to one of the four cardinal points of the compass, were used to collect pollution particles in atmosphere. Figure (2) gives a general view of one of the stations. The pollution is collected in the four containers attached at the bottom of the gauges. In monthly intervals, the collected contaminants were mixed with 500cc of distilled water and the pollution index which is defined as the mean of the conductivities of the four gauges expressed in µ S/cm and normalized to 30-day interval is calculated. This method is simple and it can be used at de- energized site without insulators. In DDG method, self-cleaning of insulators and effect of the shed profile on ESDD is not assessed, but it is inexpensive and requires no power supply, it is simple enough to be applied by local personnel. 3

4 Fig.2: Directional Dust Gauges & Specimen insulators 3-Test Results 3-1-Test Procedure The insulators and DDG instruments were exposed to natural contamination conditions in a year. ESDD-NSDD periodically measurements were done as shown in table (2). ESDD-NSDD Measurement Guide Table 2: ESDD-NSDD Measurement Guide Designation No First Measurement s Second Measurement - - s3 s Third Measurement - s5 - s Fourth Measurement s8 - s7 s6 - s9 s10 s11 s12 : ESDD-NSDD Measurement was done - : ESDD-NSDD Measurement was not done si: Sampling No (i = 1-12 ) Table 3: Contamination Site Severity Site Severity ESDD (mg/cm^2) CIGRE [4] IEEE [5] IEC [6] None Very Light Light Medium Heavy > Very Heavy Exceptional >

5 3-2-ESDD-NSDD Measurements Figures (3), (4) show ESDD, NSDD results of 30 test-stations. These data were derived from maximum ESDD-NSDD values of cap and pin insulators through four sampling periods. 3-4-Insulator Profile Effects On ESDD Figure (5) shows ESDD variations on test insulators in a year for 30 stations. Table (3) shows region classification respect to IEEE, CIGRE, and IEC Standard STATION NO Fig. 3: ESDD Measurements of 30 Test Stations s s12 SAMPLING NO s STATION NO s1 SAMPLING NO Fig. 4: NSDD Measurements of 30 Test Stations 3-6-Leakage Current Monitoring Results Figure (6) shows a sample of leakage current measurement of first station in daily and monthly periods. From the variations of leakage current, which recorded by LCM system, we could consider 5

6 HEAVY degree for this station.this study has confirmed our previous measurements and analyses St No. ins1 ped ins INS 56-3 IN56-5 LR 6 MONTH Fig. 5: ESDD Variations on Test Insulators for 30 Stations Fig. 6:Leakage Current Monitoring Of First Station 3-7-Pollution Index Based On DDG Method The DDG provides information about amount of pollution and its direction. Only the magnitude value will be considered here. Figure (7) shows pollution index for 30 stations. Fig. 7: Pollution Index for 30 Stations 6

7 4-Conclusion 4-1-Considering the maximum degree of pollution in periodical ESDD measurements based on IEC60815, 1986, the Site Pollution Severity for these stations is HEAVY degree. Operational history of existing installations in some stations like stations No 15, 16, 18 shows insulator failures in this level.therefore it is necessary to define a new criteria based on ESDD-NSDD ratio for polluted stations. Associated with mentioned criteria in figure (8) and measured values in stations No15, 16, 18 it can be conclude that the Site Pollution Severity of these stations is very heavy and this criterion is approved by operational history. Fig. 8: ESDD - NSDD Ratio on 30 Stations 4-2-It can be seen in figure (5) that pin type insulators (ANSI (56-5)) and pedestal insulators have good performance in polluted conditions. These insulators absorb less contamination than the others and cap & pin insulators are vise versa. Therefore, it is necessary to use cap & pin insulators for site pollution severity measurements. 4-3-Having compared performance of different types of insulators based on ESDD-NSDD measurements and Leakage Current Monitoring results, a correlation of Directional Dust Gauges measurement and site pollution severity can be defined. Considering pollution measurement in Azerbaijan state, which has lower pollution level than Khuzestan, helped us to complete table.4 for all of site pollution severities. Table 4: Correlation of DDG Measurements and Site Pollution Severity DDG Pollution Index µ S/cm Site Pollution Severity <125 Very Light Light Medium Heavy >750 Very Heavy 7

8 4-4-Considering pollution index mentioned in figure (7) and using DDG method, contamination levels were assessed through out Khuzestan. Based on the research we replaced all of pin type insulators (ANSI (56-3)) with pin type insulators (ANSI (56-5)) in a distribution feeder close to Persian Gulf in Mahshahr, which was faced with pollution problems. No failure has been reported in 3 years. In addition, the initial cost would be returned in 4 years. 5-Acknowledgment The authors express their special thanks to Mr. Asadian, the managing director of Khuzestan Distribution Electric Company and Dr. Arabani, the chairman of CIGRE Iran, and Mr.Mohammadi and Mr.Kashi for their great supports of the research program. 6-References 1- Round Robin Monitor Study, CIGRE Taskforce , 11 August Insulator Pollution Monitoring, CIGRE taskforce , Electra no 152 February 1994, pp New Investigation On Insulation Failures In Iranian EHV Lines Located In Polluted Area, CIGRE Session 2000, M.P.Arabani, A.R.Shirani, M.Hojjat. 4- A Critical Comparison Of Artificial Pollution Test Methods For HV Insulators, CIGRE Taskforce 33-04, Electra No 64, Jan 1979 pp _ Application Guide For Insulator In A Contaminated Environment, IEEE Transaction on PAS, Sep/Oct, 1979, pp Guide For The Selection Of Insulators In Respect Of Polluted Conditions, IEC 60815, The Performance Of High Voltage Outdoor Insulation In Contaminated Environments, The Transaction of the S.A.Institute of Electrical Engineering, R.E.Macey, April 1981,pp Research And Assessment of Insulator Performance in Marine and Desert Environment, INMR, July August 2000, pp