Dynamics and Control of Electric Transmission and Microgrids

5Modeling and Analysis of FACTS and HVDC Controllers

5.1 Introduction

As mentioned in Chapter , the AC network has no inherent power controllability. The flow in a line depends on the power (and reactive power) injections at the generation and load nodes in radial networks. In a mesh‐type network (with more than one path between any two nodes) the power flow is also dependent on Kirchoff's voltage law (KVL). Transmission planning was a major exercise in the vertically integrated utilities (VIU). However, with the advent of deregulation or restructuring, transmission expansion to accommodate load growth becomes an ad hoc exercise. There are two issues: one involves the need to increase power flows in the existing right of way (RoW) and the second relates to making transmission “flexible” to accommodate modifications of power flow pattern during system contingencies. It should be noted that the maximum power that can be carried in a line depends on the maximum temperature of the conductor. This depends on the power losses in the line and the ambient temperature. The dynamic rating of a line takes into account the temperature. The power losses include both losses and the corona losses, which depend on weather conditions.

The maximum power flow that can be permitted in an AC line also depends on its length. Steady‐state stability issues limit the power flow in a line below the thermal ...