Performanceof 1-ϕGIS withandwithoutdielectric coating

In Gas Insulated Substations (GIS), a free conducting particle can approximate any shape. If the conductor surface is not smooth and rough, then dielectric strength will be lost. So, to regain the dielectric strength, which was lost, the conductor inner surface is coated with a dielectric material of epoxy resin for which the dielectric strength can be regained. In this paper, work of simulation is done forvoltage class 132kV, 145kV,220KV and 245KVin a 1-ϕGIB for Al & Cu particles and peak radial movement was found. All the simulation analysis was carried out and resultsare shown in detail.


Introduction
Across the globe, Gas Insulated Substation (GIS) is widely preferred as it offers excellent benefits compared to Air Insulated Substation (AIS). The main parameters for popularity of GIS is its safety, problems of land availability and pollution aspects. Hence, there is necessity of shifting from the AIS to GIS. It was known from the studies that almost 30% failures are caused because of contamination of particles which is by defects of manufacturing or due to transportation [1-2].There are so many merits with dielectric coating in GIB. If the inner surface is rough, then chances of failure of insulation is more as it deteriorates the dielectric strength. But with coating, the surface becomes smooth and chances of insulation failure is less, and electrical strength increases and lift-off field also increases. At the same time, the charge acquired by the particle also reduces. In this paper, the free conducting particleradial peak movement was found in 1-Φ GIB for with & without dielectric coating. The motion equation of the particle is shown as differential equation of second order given below [4-6]:

Motion of particle simulation
The Particle charging mechanism [4] for dielectric coating is shown in figure2.

Figure2.
Mechanism of chargingof a free particle on a coating of dielectric.
The lift-off field equation in case of dielectric coating is given as:

Result analysis
All the results of simulation shown are achieved for l=10mm, r=0.3mm for voltage levels 132KV, 145KV,220KV and 245KV with calculation of field for with and without dielectric coatings and are compared as depicted in Table.1 for 1-Φ GIB using advanced C language program.
It can be inferred from the results that without coating, particularly for Al particles, the mobility is higher than Cu particles due to lighter mass. However, with dielectric coating , the mobility of the particle greatly reduces as against without coating ,both for Al and Cu particles [4][5][6][7][8][9][10].This is because of the fact that coating material inhibits the mobility of the particle and it raises the breakdown voltage. There are various types of coating materials namely epoxy, RT 481, GK 115, Al2O3 etc. But in this work, epoxy resin coating of light shade 100micron thickness is used. For voltages 220KV and 245KV as depicted in table 1, no mobility of the particle was observed for without coating as the particle crosses the inter electrode gap.Figs 3 to 10 show the Peak radial movements for Al & Cu particles with coating of dielectric epoxy resin of 100micron thickness [11][12][13][14][15][16][17][18][19][20][21]. Figures 11 to 16 show the Peak radial movements for Al & Cu particles without coating.             Figure16.Movement pattern for Cu particle for 245kV.

Conclusion
Peak movement in radial direction was found at the particle locations for with and without dielectric coatings and compared and a mathematical model was developed. An advanced C program language is used for simulation. It is noticed that Al particles have higher movement than Cu particles both for with and without coatings. Due to lighter in weight, it is also observed that particles of Al are highly affected by the voltage than copper particles. The mobility of the particle is greatly reduced with dielectric coating as against without dielectric coating due to reduction in the charge possessed by the particle. All the analysis of results are done for 132KV, 145KV,220KV and 245KV and presented.