11-01-2012, 01:17 PM
POWER SYSTEM STABILITY: NEW OPPORTUNITIES FOR CONTROL
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I. Introduction
The power system networks in North America and Europe are the largest man-made
interconnected systems in the world. The Eastern Interconnection in North America that
stretches from the East Coast to almost the Rocky Mountains is the largest in terms of
geographic area covered, total installed generation capacity and total miles of transmission lines.
Moreover, all the rotating generators in one network rotate synchronously producing alternating
current at the same frequency, that is, all the generators operate together in dynamic equilibrium.
Any unbalance in the energy distribution of the system caused by disturbances tends to perturb
the system. Large disturbances, usually caused by short circuits of high voltage equipment, can
make the power system become unstable.
II. Power System Stability
A power system is a complex conglomeration of equipment all connected together electrically. A
simple description of the power system and its model is described first so that power system
stability and related control can be discussed conceptually without getting bogged down in the
details. Of course, readers must be cautioned that often the feasibility of proposed controls
depends on these details and implementation of such controls in a power system is a complex
undertaking.
2.1 Power System Model
A power system consists of a transmission network, the nodes of which can be connected to
generators or distribution feeders. The transmission network is made up of three-phase
transmission lines that carry alternating current at 60Hz (50Hz in some countries). It is a meshed
network, the mesh having developed over time and geography to provide adequate capacity to
transmit the electric power from the generators to the distribution feeders. This transmission
network can be modeled as a standard mesh circuit
2.2 Power System Control
Given the complexity of the power system and its dynamic phenomena, one would expect that
various controls have been developed over time to control various phenomena. These
developments have followed the availability of enabling hardware technologies (e.g. electronics,
communications, microprocessors) as well as the evolution of control methodologies. In this
section, a brief survey is presented of the various controls available today. The survey is neither
comprehensive nor complete but is meant to provide a general feel for the technologies being
utilized today and the phenomena that are being controlled
