Dynamic Performance of Dual HVDC Terminals (±800 KV LCC and ±320 KV VSC) at common AC busbar- Operational Experience

Raigarh-Pugalur-Thrissur HVDC link transfer bulk power over a long-distance of 1965 km from Central India to South India. HVDC scheme comprises of ±800kV, 6000 MW HVDC LCC Scheme between Raigarh-Pugalur with 1785 km of HVDC Line with dedicated metallic return (DMR) and ±320kV, 2000 MW VSC based HVDC Scheme between Pugalur-Thrissur with line length of 178 km (150km DC line + 28Km UG cable). Pugalur HVDC Terminal located in Tamil Nadu state in India. The station is unique with Dual HVDC systems of different technologies i.e. LCC HVDC & VSC HVDC located at the same premise connected electrically to the common 400kV AC bus.

The scheme has several advantages in the perspective of RE integration in Southern Region which is seasonal. The LCC is designed to carry 6000MW power in normal direction (from Raigarh to Pugalur) and 3000MW power in reverse direction (Pugalur to Raigarh). The LCC is utilized to import power from Chhattisgarh (Central India) to Tamil Nadu (Southern Region) during summer and export the RE power (from wind farms in Southern Region) to Chhattisgarh during peak wind season. Rest of the period, the LCC link is used for Bi-directional power flow as per the availability of the wind energy in the Region. The VSC link is designed to carry active power of 2000MW in both the directions and reactive power of ±1100MVar (±660 to ±1100MVAr). The reactive power compensation provided by VSC link is very helpful for the surrounding 400kV AC bus and grid. The HVDC links have been utilized in different operating mode and different power flow directions as per grid requirements by system operators.

The subject paper covers the operational experience of dual HVDC Terminal (±800 KV LCC and ±320 KV VSC) at the common busbar Pugalur in terms of dynamic response and recovery of both VSC and LCC links during faults. The fault cases pertaining to AC line faults, DC line fault on LCC link, DC line fault on VSC link have been discussed. Dynamic response of both VSC and LCC link along with fault ride through capability and response of VSC reactive power controller has been discussed. The response of field faults is further compared with response studied during the dynamic performance study performed using EMTDC offline simulations, to the extent possible. During the offline EMTDC simulations utmost care was taken to include integrated simulations using the as-built control models of both the LCC and VSC schemes. It may be noted that the faults simulated in offline EMTDC simulations are ideal cases in terms of fault impedance, AC network conditions and fault duration while the field responses are with actual AC network fault levels and different fault impedance. The performance of dual HVDC system at common AC bus Pugalur during faults has been found satisfactory and is in line with intended control and protection response and ramp rates for different fault events. Dynamic reactive power support of VSC was also generally in line with intended performance. The link has shown successful fault ride through capabilities and recovery of systems is satisfactory.