Elmo Price

Exploring the IEEE Standard C37.118–2005 Synchrophasors for Power Systems

IEEE Standard 1344-1995 [1] on measurement of synchronized phasors of power system currents and voltages has been revised and published as IEEE Standard C37.118-2005 [2]. This paper has been prepared by the IEEE Working Group who developed the revised version. The purpose of the paper is to acquaint the power engineering community of the availability and content of this new standard, highlight some of the key differences between the old and new versions, and introduce several applications of this powerful technology.

Practical considerations for implementing wide area monitoring, protection and control

The purpose of this paper to provide a brief overview of wide area monitoring, protection and control systems addressing the fundamental process of collecting and delivering the synchrophasor data to the application, a vision of the technology direction, and some practical points to consider when implementing a phasor measurement program. It is based on experience gained working with utilities in their initial efforts to implement phasor measurement projects.

Use of synchrophasor measurements in protective relaying applications

The IEEE PSRC System Protection Subcommittee Working Group C14 has produced a report that describes practical applications of synchrophasors in protection applications. The report begins with the history of synchrophasors and then goes into issues to consider in their application. Some existing applications are described and then future applications that have been considered or are in development are described. The appendix contains applications that use synchrophasor data but are not considered protection applications. This is a summary of the complete report found on the PSRC website (http://www.pes-psrc.org click on Published Reports).

Complementary Approach for Reliable High Speed Transmission Line Protection

Line distance protection technology has evolved from sound operating principles using phase comparators used in electromechanical relays to the present day relays using microprocessor technology. Initial microprocessor relays used full cycle Discrete Fourier Transformation to extract the fundamental phasors from sampled analog data and apply them in comparator equations to determine impedance reach. This technique is still being used in most the modern microprocessor relays today. In order to address the effects of dc offset and CCVT transients a compromise is however required between operating speed, reach and security. Also, their performance is relatively independent of Source Impedance Ratio (SIR) once the transients have subsided, usually in two to three cycles. A totally different approach was introduced in 1997 using a time domain algorithm that mimics the operation of the electromechanical phase comparator. This algorithm proved to be one of the fastest and most secure for protection of medium and long lines typical for distance protection applications. The only compromise with this algorithm is the higher operating time for very short lines with high Source Impedance Ratios. This paper discusses the relative performances of each of the above approaches individually and about the advantages of combining the two algorithms to run in parallel.

A tutorial on ferroresonance

Ferroresonance is a widely studied phenomenon but it is still not well understood because of its complex behavior. It is “fuzzy-resonance.” A simple graphical approach using fundamental frequency phasors has been presented to elevate the readers understanding. Its occurrence and how it appears is extremely sensitive to the transformer characteristics, system parameters, transient voltages and initial conditions. More efficient transformer core material has lead to its increased occurrence and it has considerable effects on system apparatus and protection. Power system engineers should strive to recognize potential ferroresonant configurations and design solutions to prevent its occurrence.

Justifying pilot protection on transmission lines

This paper concerns the justification of the use of pilot protection on transmission lines.

The Performance of Faulted Phase Selectors Used in Transmission Line Distance Applications

The reliable performance of faulted phase selectors to identify the faulted phase or phases and appropriately block or permit tripping is critical to the application of distance protection. The most difficult fault type to identify correctly is a two-phase-to-ground fault. Incorrect detection methods of this fault type has lead to undesired overreaching and/or tripping for remote two-phase-to-ground faults beyond the underreaching zone reach setting. It is also important to provide accurate fault location and record correct faulted phase information after the fault has cleared to correctly access the fault type characteristics. This paper analyzes the issues related to two-phase-to-ground faults and discusses several methods used for faulted phase identification and the advantages and disadvantages of each. It also shows how different phase selection methods may be used to complement each other to provide more reliable faulted phase identification.

Achieving optimum capacitor bank protection and control

TVA applies shunt capacitor banks to their 161 kV system to regulate the local substation bus voltage over a range of light to heavy load and load switching conditions. The substation capacitor bank configuration may consist of up to 6 separately switched capacitor stacks. The entire substation bank is switched with a circuit breaker. The voltage level is monitored and used to switch in and out capacitor stacks as required for correct VAR compensation. The bus voltage is regulated to operate within a defined bandwidth around nominal voltage. There are two operating band widths that are used depending on load conditions, narrow band (NB) and wide band (WB). The number of capacitor bank stacks and bandwidths are determined by System Operations and Planning. Capacitor stack switching is either done manually or automatically. Automatic control must address several issues. Some of these are hunting - trying to find a stable voltage within an operating bandwidth, bandwidth operation transfer, auto to manual transfer and balanced switching operations of up to six capacitor bank capacitor switches over the life of the bank.

The negative branch impedance in the transformer sequence circuit model

The negative branch impedance of the transformers T branch model was investigated as to its effects on current reversals in the delta tertiary winding and transformer neutral. Along with the negative branch values small positive values allowed current reversals in the transformers neutral. Given the importance of accuracy the model should be developed with zero sequence impedances derived from zero sequence testing. It was also pointed out how transformer design affects the T branch model. Generally the negative or low impedance is on the low voltage side of the transformer model. However, different winding configurations can eliminate or even move the negative impedance to the high voltage side. The latter case being possible or even likely for transformers with high H/X turns ratios (e.g. 345/34.5/13.8 kV).

Protecting transmission lines terminated into transformers

Transmission lines that are terminated into transformers are applications where the line and transformer cannot be separated by a circuit breaker and are therefore in the same zone of protection. These applications may be addressed with either current differential or line distance protection. In either case the implementation of separate transformer differential protection isolating the protection zone is recommended. The line protection application needs to consider the instrument transformer locations and transformer winding connections at the transformer end. This paper will discuss the application considerations for both line differential and distance schemes for lines terminated into transformers and provide application guidelines.