Flashover and partial discharge characteristics of fiber of valve tower in converter station

Thyristors of valve tower in converter station are controlled through fiber. Valve fiber withstands strong electric field and harmonic voltage. Partial discharge (PD) and flashover faults sometimes happen in valve tower. In this paper, flashover test is conducted for different fiber sheath materials under different voltage types (DC voltage and harmonic voltage superimposed on DC voltage). PD characteristics of fiber under combined voltage of AC voltage and DC voltage are measured. And influence of sheath materials on the PD inception voltage is discussed. Test results indicate that the flashover voltages of fiber sheath materials are different under different voltage types. Sheath material with higher surface resistivity has higher flashover voltage under DC voltage. Moreover, PD of fiber under vertical electric field concentrates on the falling edge of the positive half-circle of the AC voltage, and the PD strengthens with the increase of DC voltage. And the sheath material whose ratio of volume resistivity to relative dielectric constant is approximate to that of the fiber body (SiO2), has higher PD inception voltage.