Design Modification of Spacer and Conductor Structure for Reducing Electrical Stress on 150 kV Three-Phase GIS Spacer

This paper reports electric field intensity minimization in a three-phase 150 kV GIS spacer with aim to reduce the maximum electric field intensity (Emax) in the spacer, especially around the triple junction area, where conductor, spacer, and SF6 gas meet. The three modifications of the GIS spacer and the conductor structure are performed to reduce electric field in the GIS spacer. First, the distance between phase conductors (d) is changed with varied ratio of 0.8, 0.9, 1.1, 1.15, and 1.2 times of original distance (d0). The original distance between conductor phase-S and T and phase-S and R is 206 mm, while the distance between conductor phase-R and T is 260 mm. The configuration of the conductors is also varied. The type of triangles all three conductors form is changed from an isosceles triangle (the original configuration) to an equilateral triangle. The distance between conductors in the new equilateral triangle configuration is varied from 230 mm, 250 mm, 270 mm, to 290 mm. The last parameter changed for modification in the spacer form is contact angle. The contact angle (θ) refers to the angle between the spacer-HV electrode side and the spacer-grounded electrode side. This angle is varied from 75° to 60°, 45°, and 30°. The result shows that the Emax in the spacer which is originally 138 kV/cm can be reduced from 10% up to 59%. The results show that the modification performed by controlling the phase conductors gave the Emax of 131 kV/cm when the distance between phase conductors is 1.15 times of the original distance of the unmodified spacer. A combination of modifying the distance and triangle configuration of phase conductors has reduced the Emax to 118 kV/cm. It is achieved when the phase conductors have equilateral triangle configuration with distance between conductors is 270 mm. The most significant reduction in electric field intensity is given by the modification contact angle between spacer, conductor, and SF6, that can reduce the Emax to 97 kV/cm at contact angle of 75°.