Research On The Effect Of The GIL Ground Electrode Coated Dielectric Layer On Movement Of Metal Particles

Metal particles may be inevitably produced in the process of production,transportation,installation and operation in GIS/GIL.Driven by the electric field force,metal particles will move between the electrodes and cause partial discharges to damage insulation performance of the system,even adhere to surface of insulator,shortening electrical insulation distance along surface of the insulator,distoring electric field on the surface of insulator,and initiating gas gap breakdown or insulator surface flashove.Research on the pollution of metal particles in GIS/GIL is carried out,mainly to study the suppression effect of the ground electrode coating dielectric layer on metal particles and its influencing factors.A platform for simulating particle movement and aging tests was built.The motion platform can provide a stable gas environment,and realize acquisition and measurement of images,vibration signals and UHF signals.In aging test platform,according to the principle of accelerated aging sample preparation,thermal aging,electrical aging and combined electrical and thermal aging of dielectric layer are realized.At the same time,a simulation model of particle movement in a uniform electric field is established..Based on the above-mentioned test platform,the movement characteristics of particles in the electric field are first studied.The ground electrode coated with a dielectric layer can increase lifting field strength of particles.On the one hand,the dielectric layer obstructs charge of particles,on the other hand,it generates an additional force o to prevent relative movement of particles.Influencing factors of the particle suppression effect of the dielectric layer are studied.When thickness is less than or equal to 200μm,increasing the thickness of dielectric layer can increase lifting field strength of particles.Improvement of dielectric properties can increase the lifting field strength of particles.Lifting field strength of particles on the bare electrode is not affected by type of voltage,but when electrode is coated with a dielectric layer,lifting field strength of particles in the AC system is much higher than that of particles in DC system,increased to 7～10 times that of DC.In AC system,increasing air pressure will significantly increase suppression effect of layer on particles,but in DC system,improvement of lifting field strength is very small.Influence of electrothermal aging on the particle suppression effect of the dielectric layer is studied.Thermal aging will weaken the barrier effect of the dielectric layer on the particles obtaining charge and reduce the additional force of the dielectric layer on the particles,resulting in a weakening of the suppression effect of the dielectric layer on the particles.Electrical aging only weakens the barrier effect of the dielectric layer on the particles to obtain charge,resulting in a weakening of the inhibition of particles by the dielectric layer.Thermal aging and electrical aging are independent processes,but electrothermal aging will cause the aging speed to increase and the aging degree to deepen.The additional force of unaged viscous medium layer on spherical particles is 10-3～10-2N,which is much larger than gravity of particles and electric field force before the gap breakdown.The viscous medium layer can achieve the purpose of completely suppressing movement of metal particles.With the progress of thermal aging,the viscous medium layer’s suppression effect on moving particles will rapidly decrease.Experimental studies have shown that the ground electrode coated with a viscous dielectric layer can significantly improve the suppression effect of dielectric layer on the movement of particles,and the effective duration can be about 60,000 hours,which has certain engineering application significance.