Replacement of 400kV, 63 MVAR Aged Reactor with 400kV, 125 MVAR Reactor on the Same Foundation: Challenges, Modifications, and Lessons Learnt

Transmission assets are becoming old and the ageing factor is affecting their performances. The increasing demand for reliable and efficient power transmission has necessitated the modernization of critical substation components with higher ratings. This paper focuses on the replacement of a 33 years old 400kV, 63 MVAR Bus Reactor (Shunt Reactor) with a highercapacity 400kV, 125 MVAR Bus Reactor on the same foundation at POWERGRID Gooty

Substation due to presence of Furan content resulted by Insulation degradation. The challenges, foundation modifications, and lessons learned during this replacement are comprehensively documented, providing valuable insights for similar projects in the future.

The project aimed to achieve three key objectives: (1) Replacement of the old 63 MVAR reactor with a 125 MVAR reactor to meet increasing grid demands, (2) Reuse the existing foundation with structural modifications to reduce costs and project time, and (3) Complete the replacement with minimal interruption time. The existing foundation, originally designed for the smaller reactor, required additional assessment and modification to accommodate the increased size, weight, and operational forces of the new reactor.

The technical challenges encountered during the project are discussed in detail. These include the increased dimensions and weight of the 125 MVAR reactor, the limited space in the substation yard, and the constraints of completing the replacement within a tight outage window. Also, the old Reactor had a separate cooler bank (Radiators) arrangement whereas the new Reactor is having a body mounted arrangement.

A portion of the paper is dedicated to the foundation assessment and modification process.

Shear bond drilling, increased Reinforcement, high-strength concrete has been used to support the increased load. HVWS spray system (for fire-fighting) modification is also involved with new pylon supports and their foundations.

The installation phase involved precision alignment and the upgrading of electrical connections to match the specifications of the new reactor. The old Reactor had only one Buchholz relay and one Pressure Relief Device (PRD) whereas the new Reactor is having 2 nos PRDs and 2 nos Buchholz relays. Sudden Pressure rise relay is present in the new Reactor along with Some additional alarms. These things required additional cabling and terminations from Reactor to the Relays and protection system. All the Protective relays, were reconfigured for compatibility.

The commissioning process included mechanical and electrical testing, such as LVAC tests,

LVDC tests and oil parameter tests etc.

The project’s success was attributed to meticulous planning, collaboration, and the innovative reuse of existing infrastructure. Lessons learned include the importance of thorough preassessment of structural and electrical components, effective coordination among teams, and the need for contingency planning to address any unforeseen challenges.

Reusing the foundation not only reduced costs but also minimized the environmental impact.

This case study serves as a practical guide for similar modernization projects, emphasizing costefficiency, environmental sustainability, and enhanced grid reliability.