Estimation of stored energy for TWIN source HVDC transmission line

Abstract

TWIN source is a two driver based negative ion source currently operational at IPR. The two driver RF negative ion source test bed to extract and accelerate H- ion beams up to 50 keV. For Negative Neutral Beam Injectors (NNBI) utilizing RF negative ion source, grid breakdown is a routine phenomenon during system conditioning and operation phases. During the grid breakdown event, there are chances that electrostatic energy stored in the transmission line is dumped in the grids, which may possibly damage them. In case of NNBI system with long high voltage transmission line, contribution for the stored energy emanates from their inter-conductor capacitance. The inter-conductor capacitance and thus stored energy could be reduced by proper designing of the HVDC Transmission line. However, it is equally difficult and challenging to estimate the inter-conductor capacitance of the transmission line with non-generic cross sections. This paper discusses estimation of inter-conductor capacitance, an experimental set up to realize a grid breakdown and thus estimate the stored energy of a HVDC transmission line prototype (1m length). The HVDC transmission line prototype (1m length) has vertical placement of conductors. Inter-conductor capacitance is estimated for vertical topology. The stored energy values from estimated inter-conductor capacitance value is compared with experimental results for HVDC transmission line prototype (1m length). Also, modeling of HVDC transmission line is done to simulate a grid breakdown and thus compute the stored energy for entire transmission line length (120m).