DC Line Fault Recovery Performance of the India’s first ±320kV VSC HVDC Pugalur-Thrissur Link

(Kerala state) has been designed to transfer DC Power of 2000MW at ±320kV DC Voltage through an overhead DC line (150 km) and DC Underground Cable (28 km). The transmission system consists of two (2) symmetrical monopoles with Modular-Multilevel Converter (MMC) topology using half-bridge sub-modules. The VSC link is also capable of reactive power of

±1100MVar.

The VSC link was commissioned in year 2021 and has been in service since last five (5) years.

Pugalur - Thrissur VSC HVDC transmission line is a combination of overhead line and DC cable, a safe, economic, and reliable fault recovery ability of the HVDC system is essential along with a selective fault detection between overhead line and cable. During DC faults, unlike the LCC Converters (Thyristor Valve), blocking of the VSC converters can neither cut off fault currents, nor de-energize the DC circuit as MMC with half bridge sub-modules represents an uncontrolled diode rectifier during blocked condition. In case of a fault on these lines, the VSC

HVDC system shall clear the fault and recover operation.

This paper presents a field-validated evaluation of DC line fault recovery performance for a

±320 kV, 2000 MW VSC-HVDC system with a hybrid overhead line and underground cable configuration. The key contributions are: (i) analysis of actual transient fault recorder data obtained during nearly five years of commercial operation, (ii) quantitative benchmarking of recovery performance against project specifications and established industry requirements, and

(iii) demonstration of the effectiveness of a selective DC line fault recovery strategy for half-bridge MMC-based VSC-HVDC systems under pole-to-ground fault conditions. The results provide practical insights applicable to future VSC-HVDC projects with mixed transmission corridors.