  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.
