An intelligent load shedding approach to enhance the voltage stability of a power system

Abstract

Load shedding can be defined as a coordinated set of controls which result in the decrease of electric load in the system. Load shedding may be initiated due to two reasons: (1) Frequency; (2) Voltage.One of the differences between the two problems is--The frequency problem is a system-wide phenomena affecting the entire electrical island, whereas the voltage problem is generally localized.The present day utility philosophy considers load shedding as a last resort in the emergency control of the system. This is understandable because the shedding of a load leads to dissatisfied customers, decreased revenues, bad publicity, and possible litigations (depending upon the seriousness of the incident). Utilities try to avoid it as much as possible.The objective of this dissertation is to perform an exhaustive study of the areas of load shedding and load management and recommend techniques for improvement (for the voltage problem). Two main accomplishments are presented. They are: (1) Expert Load Shedding (ELS), an intelligent operator's aid to help in load shedding is the result of the study of current load shedding practices, and intelligent methodologies. The method suggested in this document has been designed for implementation in an Energy Management System (EMS) environment. A prototype of the ELS has been implemented in the Dispatcher Training Simulator (DTS) which simulates an EMS environment. Preliminary results of tests performed using the ELS on an enhanced version of the New-England 345-kV system has proved very promising. (2) Expert Load Management (ELM) is an expert system which has been used to provide load relief (in a distribution system) in an emergency mode. Load Management (LM) is an application in the Distribution Automation (DA) system which involves the process of controlling utility system loads by the remote control of individual customer loads. This expert system has been implemented in the EMS/DA environment and tested on the ODEC (Old Dominion Electric Cooperative) system. Preliminary results of the tests performed have proved very promising.The main reason for the development of ELS and ELM are to enable the eventual linking of the two functions. It is the author's contention that a link between load shedding in the EMS and load management in the DA it would be possible to obtain load relief without actually tripping feeders.