Study On Parallel Gap Lightning Protection Devices For Insulator Strings Of Overhead Transmission Lines

Faults induced by lightning stroke on the transmission line become a global difficult problem in the power supply security. To improve the lightning impulse withstand level and to reduce lightning trip-out rate of transmission is the main measures taken in our country for lightning protection nowadays. Those traditional measures are conservative and one-sided when our power grid structure is stronger now. Therefore, it is significant to study an effective and practical parallel gap lightning protection device (PGLPD) for lightning protection.Aim for a well performance PGLPD, this thesis acquires the ratio of 220 kV composite insulators and PGLPD gap length via experimental study. Research shows: the lightning impulse voltage-time characteristics of composite insulators without shielding rings and stick type PGLPD are abrupt; when the gap length of PGLPD is 1700mm~1800mm, which is 11.94%~16.83% shorter than the dry arcing distances of insulators, the lightning impulse voltage-time characteristics of stick type PGLPD is lower than of insulators, so insulators can be protected effectively, but the protection margin is small.Based on the arc chain model, the arc movement model with consideration of thermal buoyancy is set up. As a validation, simulation of arc movement in the PGLPD on 110 kV overhead transmission line is conducted and shows good correspondence with experiment results. The proposed model can explain the jumping phenomena of up root owing to short-circuits between the up root and arc column successfully. In addition, arc movements under different amplitudes of current and different structure types are done. Results suggest that the larger short-circuit current is, the less time the arc motion lasts. A smooth shape of the electrode is beneficial to the shift of the arc.Take 220 kV composite insulators as example, the author adopt finite element method to establish a three-dimensional electric field calculation model of composite insulators in the transmission line. Then, the impact of different type of PGLPD on the distribution of voltage along insulators is analyzed. Besides, the author makes a comparison of voltage distribution along insulators when PGLPD and shielding rings is employed, separately. Results are as follows: the performance of ring type PGLPD is better than of stick type PGLPD. For ring type PGLPD, the effect of improving electric field on the end of the insulators is better when the pipe diameter is bigger and ring diameter is smaller. And the effect of improving electric field on the end of the insulators is better only when the insertion depth of PGLPD. Besides, a conclusion can be obtained is that it is feasible to use ring type PGLPD as an alternative of shielding rings.