Open Line Test Application in UhVDC for Condition Monitoring of Insulation health of Ultra high Voltage Equipments

Open Line Test is used in Ultra High Voltage DC Transmissionsystem to test the voltage insulation capability of a line or a converter after an extended period of de-energization or after recovering from insulation faults. It is done in order to avoid converter startup towards a solid ground fault. OLT can be done on the internal dc pole bus in each station/converter or in the dc line. To perform OLT, converteris deblockedin open circuit condition and the dc voltage is increased to the desired reference level at a predefned ramp rate. DC voltage reference level and the voltage ramp rate are operator selectable. For any kind of persisting insulation fault, the converter fails to build up the dc voltage across the pole to neutral.

To understand the behavior of HVDC system during OLT, modeling and simulation for following converter confgurations have been done

(a) Converter is connected to DC bus without DC filter and without DC line.

The simulation results thus obtained have been compared with the actual OLT operation results.This paper analyses the application of the results of the Open Line Test as an effective tool for condition monitoring of the insulation health of HVDC equipments.