# Security Constrained Multi-Stage Transmission Expansion Planning Considering a Continuously Variable Series Reactor

## TL;DR

This paper proposes a novel multi-stage transmission expansion planning model incorporating cost-effective Continuously Variable Series Reactors (CVSRs) with security constraints, using linearization and decomposition techniques for large-scale systems.

## Contribution

It introduces a linearized mixed-integer model for TEP with CVSRs and a decomposition method to handle large systems efficiently.

## Key findings

- CVSRs significantly enhance planning flexibility and reduce costs.
- The proposed approach is effective on IEEE 24-bus and Polish 2383-bus systems.
- Decomposition reduces computational burden without guaranteeing global optimality.

## Abstract

This paper introduces a Continuously Variable Series Reactor (CVSR) to the transmission expansion planning (TEP) problem. The CVSR is a FACTS-like device which has the capability of controlling the overall impedance of the transmission line. However, the cost of the CVSR is about one tenth of a similar rated FACTS device which potentially allows large numbers of devices to be installed. The multi-stage TEP with the CVSR considering the $N-1$ security constraints is formulated as a mixed integer linear programming model. The nonlinear part of the power flow introduced by the variable reactance is linearized by a reformulation technique. To reduce the computational burden for a practical large scale system, a decomposition approach is proposed. The detailed simulation results on the IEEE 24-bus and a more practical Polish 2383-bus system demonstrate the effectiveness of the approach. Moreover, the appropriately allocated CVSRs add flexibility to the TEP problem and allow reduced planning costs. Although the proposed decomposition approach cannot guarantee global optimality, a high level picture of how the network can be planned reliably and economically considering CVSR is achieved.