Operational Experience of Steady-State and Dynamic Reactive Power Capabilities of the Pugalur–Thrissur VSC-HVDC System

Nadu) and Thrissur (Kerala) using Voltage Source Converter (VSC) technology. This link, featuring two symmetrical monopoles, enables 2000 MW of power transfer (1000 MW per pole) and supports ±330 MVAr reactive power during steady-state operation. It employs a hybrid transmission system combining 138 km of overhead line and 27.2 km of underground cable, with a transition station facilitating the changeover. The converter stations are based on

Modular Multilevel Converter (MMC) design using half-bridge topology, where numerous submodules are series-connected to generate output voltage.

The paper analyses the steady-state and dynamic reactive power control features of the VSCbased HVDC system, evaluating two steady-state strategies: Reactive Power (Q) Control, where each converter regulates reactive power according to operator-defined setpoints, and

Voltage Sensitive Modulation (VSM), where converters adjust reactive power in response to

AC voltage fluctuations to maintain grid voltage within set thresholds. The study also assesses the system’s AC fault management capabilities. AC voltage control uses the positive phase sequence component measured on the AC side of the converter transformer. Specific AC voltage ranges are defined to coordinate control priorities. During fault conditions, dynamic support of reactive power is achieved through reactive reference current modulation based on converter characteristics.

Operational experience since the system’s commissioning shows that the VSCs perform effectively in regulating voltage, operating in both capacitive and inductive modes depending on real-time grid needs. This ensures grid stability not just locally, but also in adjacent substations. The improvement in the voltage profiles at nearby nodes under varying load and 1 weather conditions has been assessed using PMU data, since the commissioning of the VSC system.

The paper further investigates the VSC’s dynamic behaviour during grid faults using data from

Transient Fault Recorders (TFR), Disturbance Recorders (DR), and Phasor Measurement Units

(PMUs). A case involving a B-phase-to-ground (B-N) fault on the 400 kV Thrissur–Kochi-2 line is analysed, along with other fault types such as line-to-ground and line-to-line faults. These assessments help evaluate the VSC’s response to disturbances and its ability to enhance grid support.