Stanley H. Horowitz

IEEE Standard for Synchrophasors for Power Systems

IEEE Standard 1344, Synchrophasors for Power Systems, was completed in 1995. It sets parameters required to ensure that phasor measurement will be made and communicated in a consistent manner. It specifies requirements for the timing signal used for phasor synchronization and the time code needed for input to a measurement unit. GPS is the recommended time source and IRIG-B is the basic format used for time communication. The standard requires correlating phasors computed from unsynchronized and synchronized sampling to a common basis. Timetagging accurately and consistently is essential for wide area comparison of phase. The standard specifies information exchange and control message formats. These include data output, configuration, and command messages. It includes 7 annexes that discuss the concepts covered in the body of the standard.

Adaptive transmission system relaying

The use of digital techniques to adapt transmission system protection and control to real-time power system changes is investigated. The discussion covers transmission system protection philosophy, transmission line protection, relay settings, transformer protection, and automatic reclosing. The tradeoff between dependability and security is examined, as well as the various conflicting criteria embodied in transmission line protection. Adaptive strategies that minimize the compromises required and thereby optimize system performance are presented. >

Third zone revisited

Zone 3 of a step-distance protection scheme has been identified as one of the contributing causes of cascading failures in power systems. The National Electric Reliability Council (NERC) has issued rules, and the IEEE Power System Relaying Committee (PSRC) has discussed recommendations to reduce the undesirable operation of this component of the protection chain. It is the purpose of this paper to reexamine the application of zone 3, to describe situations where it can be properly utilized, where it can be removed without reducing the reliability of the system protection and, if used, how it can be modified or set. A table is presented for a variety of station designs and protection schemes including two common local backup relay systems and the associated application of a remote third zone. Finally, the concept of critical locations is introduced which can assist the relay engineer in determining if potential zone 3 undesirable operations are a serious threat to the system and help determine if the expense and difficulty of removing zone 3 or modifying the relay or its associated station is justified.

Some applications of phasor measurements to adaptive protection

The application of microprocessor-based phasor measurements to novel adaptive protection schemes is presented. The concepts of digital adaptive protection in which relay characteristics are modified in response to external signals and conditions in the system, are examined. The importance of real-time phasor measurements in adaptive protection systems is illustrated by two examples. The first involves obtaining synchronizing information about phasor measurements to be used for current differential protection of a multithermal line. By estimating the reference angles for the phasor measurements the effect of synchronized sampling can be obtained without the expense of synchronizing equipment. The second use is the adaptive setting of out-of-step blocking and tripping. Traditional approaches experience problems because the settings are, of necessity, compromises based on offline studies. By reacting to real-time phasor measurements from selected buses in interconnection, it is shown that improved out-of-step blocking and tripping is possible. >

Boosting immunity to blackouts

There have been several key developments that make it conceivable that it would soon be possible to reduce the frequency and intensity of interconnected power system failures. System protection is one of the technologies undergoing radical changes that holds a strong promise that cascading system outages can be mitigated or even eliminated. The increasing use of digital relays that will allow the implementation of exciting new concepts has made this a strong possibility. In this article, we report on future concepts in power system protection, communication, wide area measurement systems (WAMS), system control, and electricity market considerations, Adding a summary of our own research in associated studies and our assessment of future investigations, our aim is to provide a blueprint for a secure power system infrastructure.

The Future of Power Transmission

This paper discusses the future of power transmission in U.S. The revolution in distribution must be accompanied by the continued evolution of the transmission system. It is to find the political alignment that is needed to accept the vision and move forward aggressively. For transmission, that means recognizing that new lines, not just better lines, will be needed. United States has allowed fragmented responsibility for transmission additions to slow the process to an unacceptable extent.

Limits to Impedance Relaying

The paper reviews the role of impedance relaying in modern transmission line protection systems. The speed and reach of the first zone of an impedance relay are identified as being the most important attributes of a relay. The paper develops a mathematical model of the relaying process in the presence of transient phenomena which accompany faults. It is shown that there is an uncertainty associated with the impedance estimated by a relay and this uncertainty depends upon the speed with which these estimates are made. A quantitative relationship between the relay speed and its reach is obtained.

Turbine-Generator Shaft Torques and Fatigue: Part I - Simulation Methods and Fatigue Analysis

This paper is the first of two papers concerned with the effects of power system disturbances and operating practices upon turbine-generator shafts. The paper presents techniques for the analysis of shaft fatigue damage due to torsional oscillations. The detailed development of a fatigue model is presented. An example illustrates the use of the techniques for calculation of the loss of life of a turbine-generator shaft due to high speed reclosing of a close-in three phase fault.

System-wide Protection

By its very definition, as applied to power system protection, wide-area measurement systems (WAMSs) are a synergistic combination of relays, measuring instruments, control equipment, automation equipment, monitoring equipment, and communication employed to encompass extensive system elements as opposed to the more traditional view of individual equipment or point-to-point protection. The increasing world-wide application of digital devices and high-speed wideband communication and global positioning systems (GPSs) plus the growing acceptance of adaptive relay protection philosophy and practice have dramatically altered the fundamental role of power-system protection.

Frequency Actuated Load Shedding and Restoration Part II - Implementation

Power systems must be operated within limits that will ensure adequate generation and transmission capacity to avoid cascading. In developing a set of operating limits, it is important to do so within a general framework in order to ensure that the operating objectives are met. In this regard, a set of general guidelines are presented below: 1. The integrity of the transmission system will be maintained at all times without planned internal separation. 2. Maximum reasonable assistance will be given to adjacent systems experiencing difficulty. However, such assistance will be terminated ?without opening interconnection circuits ?when the reliable operation of the assisting system is impaired. 3. The system should be operated so that the occurrence of the next single contingency (outage of tower, circuit, unit, breaker, bus, etc.) will not result in a cascading loss of the bulk transmission system. The single contingency is continually geared to the current state of the system and reflects maintenance and forced outage events as they occur. In addition, when evaluating overload contingencies, the time to relieve the stress must be compared to the permissible degree of overload. 4. When the system experiences a generation-load imbalance, the principles of sound interconnected operation will be maintained by bringing under control an unscheduled tie-line power flow condition as quickly as possible.