Phasor Measurement Techniques.- Phasor Estimation of Nominal Frequency Inputs.- Phasor Estimation at Off-Nominal Frequency Inputs.- Frequency Estimation.- Phasor Measurement Units and Phasor Data Concentrators.- Transient Response of Phasor Measurement Units.- Phasor Measurement Applications.- State Estimation.- Control with Phasor Feedback.- Protection Systems with Phasor Inputs.- Electromechanical Wave Propagation.

Synchronized Phasor Measurements and Their Applications

Synchronized phasor measurements have become a mature technology with several international manufacturers offering commercial phasor measurement units (PMUs) which meet the prevailing industry standard for synchrophasors. With the occurrence of major blackouts in many power systems around the world, the value of data provided by PMUs has been recognized, and installation of PMUs on power transmission networks of most major power systems has become an important current activity. This paper provides a brief introduction to the PMU and wide-area measurement system (WAMS) technology and discusses the uses of these measurements for improved monitoring, protection, and control of power networks.

Synchronized Phasor Measurement Applications in Power Systems

A significant increase in the penetration of distributed generation has resulted in a possibility of operating distribution systems with distributed generation in islanded mode. However, overcurrent protection of an islanded distribution system is still an issue due to the difference in fault current when the distribution system is connected to the grid and when it is islanded. This paper proposes the use of adaptive protection, using local information, to overcome the challenges of the overcurrent protection in distribution systems with distributed generation. The trip characteristics of the relays are updated by detecting operating states (grid connected or island) and the faulted section. The paper also proposes faulted section detection using time overcurrent characteristics of the protective relays. Simulation results show that the operating state and faulted section can be correctly identified and the protection system settings can be updated to clear the faults faster.

A Simple Adaptive Overcurrent Protection of Distribution Systems With Distributed Generation

Reach accuracy of a distance relay on transmission lines is adversely affected by fault resistance combined with remote-end infeed which is not measurable at the relaying point. Different network conditions correspond to different remote-end infeed behaviour and in conventional setting a safety margin is necessary so as to avoid maloperation. In this paper an adaptive setting concept which can overcome this disadvantage is proposed. A microprocessor based distance relay with this new technique can respond to network conditions that change from time to time and computer simulation has confirmed the validity of this new concept. >

Adaptive relay setting for stand-alone digital distance protection

Many methods for fault location using synchronized phasor measurement have been reported in literature. Most of these methods use voltage and current measurements at one or both ends of a transmission line. Accuracy of current measurement is limited by the accuracy of the current transformers (CT) used. This paper describes a fault-location method for transmission lines using only synchronized voltage measurements at both ends of the line, eliminating the inherent error due to CT. The method can be applied to transposed and untransposed lines. The method is tested using results from a steady state fault-analysis program and EMTP.

Fault location on a transmission line using synchronized Voltage measurements

Concepts for adaptive protective relaying of transmission lines are presented. These include changes in online relay settings, relay characteristics, or logic in response to power system or environmental changes, or as a result of operating experience. Such changes as line-out or generator-out contingencies, which affect fault current distributions and degrade the system's security level, initiate adaptive protection system responses. Adaptive relaying is shown to be capable of improving relaying reliability and power system security and of achieving better utilization of transmission facilities. Most of the concepts require a hierarchical computer system, involving front-line parallel processors, a substation host, and remote central processors, all linked by channels that transmit data or relaying changes prior to or after a disturbance. It is suggested that maximum value from adaptive relaying will result from integration with existing or planned substation control and data acquisition functions and interfacing with the central energy management system (EMS). Emphasis is placed on use of interim hardware approaches to allow evolutionary development. >

J.R. Linders

Papers

Adaptive transmission relaying concepts for improved performance