Hector J. Altuve

A Current-Based Solution for Transformer Differential Protection. Part I: Problem Statement

This paper analyzes the problem of transformer differential protection. First, we review the concept of transformer differential protection. We then analyze magnetizing inrush, overexcitation, and current transformer (CT) saturation phenomena as possible causes of relay misoperation. Finally, we summarize the existing methods for discriminating internal faults from inrush and overexcitation conditions. In Part II of the paper we propose a new approach for transformer differential protection and describe the relay that is based on this approach.

Advances in series-compensated line protection

In this paper, after an overview of transmission line series compensation, we review series-compensated line protection challenges, that include voltage inversion, current inversion, and distance estimation errors. We then present modern solutions to improve directional, distance, and differential element operation on series-compensated lines. Later we provide relay setting guidelines. Finally, we present and discuss several cases of protection scheme operation for actual faults.

A Current-Based Solution for Transformer Differential Protection Part II: Relay Description and Evaluation

This paper describes a new approach for transformer differential protection that ensures security for extemal faults, inrush, and overexcitation conditions and provides dependability for internal faults. This approach combines harmonic restraint and blocking methods with a wave shape recognition technique. We compare in the paper the behavior of some traditional transformer protection methods to that of the new method for real cases of magnetizing inrush conditions.

Protecting mutually coupled transmission lines: Challenges and solutions

This paper is a tutorial on the protection of mutually coupled transmission lines. It discusses how mutual coupling affects the polarizing quantities of ground directional elements, the reach of ground distance elements, and the accuracy of single-ended fault locating algorithms. The paper provides settings guidelines for instantaneous directional overcurrent and ground distance elements. It discusses in detail how transmission line mutual coupling causes overreaching or underreaching of ground distance elements. It also discusses the impact on these elements of grounding the mutually coupled line at both line ends during maintenance. The paper analyzes whether mutual coupling compensation offers any benefits to line protection. The ease and benefit of line current differential schemes are contrasted in the discussion. Lastly, the paper examines a case when a double-circuit transmission line is operated as a single circuit with jumpers placed across similar phases along the line. This situation typically arises when the utility company needs to free one of the bays to bring an additional line into the substation. The protection engineer needs to decide where to install jumpers to parallel the two circuits in order to avoid distance element underreaching. The paper provides an analysis of this problem and offers suggestions on how to address it.

Dynamic simulations help improve generator protection

This paper describes a digital simulation study of a set of two 160 MW generating units operating in the Juan de Dios Batiz Paredes thermal power station, in Topolobampo, Sinaloa, Mexico. This plant belongs to Comision Federal de Electricidad, the national Mexican utility. We first discuss the factors that limit the active and reactive power delivered by a generating unit, such as thermal and voltage limits, power-system imposed limits, and the minimum excitation limiter. We then describe generator protection functions related to the capability curve. Later, we propose a P-Q plane-based scheme that provides generator loss-of-field protection and capability-curve violation alarming. Finally, we present the simulation results of loss-of-field and loss-of-synchronism conditions of one of the two generating units for several cases, including different initial load conditions, different loss-of-field modes, and different numbers of units on line.

Sizing current transformers for line protection applications

This paper discusses the factors to consider for sizing current transformers (CTs) for line protection applications. We first cover CT basics, with emphasis on errors and ac and dc saturation. We also discuss the criteria to avoid CT saturation. Then we analyze the effect of CT saturation on overcurrent, distance, directional, and differential elements. Further, we present the advances in protection element design to improve security and speed under CT saturation conditions. Finally, we discuss the tools available to the protection engineer for CT sizing and provide some guidelines.

Negative-sequence differential protection - principles, sensitivity, and security

This paper explains the principles of negative-sequence differential (87Q) protection, its basis for excellent sensitivity and speed, and the need for securing it with external fault detectors to deal with the saturation of current transformers. The paper reviews applications of 87Q elements to lines and transformers. It explains why 87Q elements cannot be used for turn-to-turn fault protection in shunt reactors and stators of generators and motors. The paper presents applications of negative-sequence directional elements for turn-to-turn fault protection in reactors and stators. Finally, it derives two new protection principles based on negative sequence for generator turn-to-turn fault protection.

Updated transmission line protection communications

The telecommunications revolution has increased the options and capabilities available for communications-based protection of transmission lines. To improve tripping speeds on long and short lines, protection engineers can select from a host of media, protocols, and logic schemes. The question to address is what communications scheme is best for which circumstances. This paper begins by establishing performance baselines of protection scheme operating times measured in event reports for a variety of in-service lines. It includes various successful systems and takes into account all of the elements that must be addressed when engineering a protection scheme, such as relay pickup time, communications interface and latency, coordinating time delays, and sequential tripping times. These in-service schemes are compared with laboratory tests of new systems, using radio and fiber-optic communications with serial and Ethernet protocols. Methods of optimizing different systems are tested and evaluated; the final results are tabulated and compared. No single scheme is best for all circumstances. With comparison data, the protection engineer can select the best options to improve the overall power system performance. Recognizing the strengths and weaknesses of different schemes assists the engineer in addressing new situations. Comparing laboratory tests and in-service performance provides a tool for evaluating a transition to new technologies.

Directional Comparison Protection Over Radio Channels for Subtransmission Lines: Field Experience in Mexico

In this paper, we first review the need for communications-assisted protection of subtransmission lines, describe the communications channels available, and compare applicable protection schemes. We show the advantages of directional comparison protection over digital point-to-point radio channels for this application. Later we present a summary of the applications of directional comparison protection over radio channels in Mexico. We also provide statistical data on the field performance of protection schemes and radio channels installed in Mexico. We then present and discuss several cases of protection scheme operation for actual faults. Finally, we provide guidelines for applying directional comparison protection over radio channels to subtransmission lines.

Correction to "A current-based solution for transformer differential protection-part II: relay description and evaluation"

In the above paper, a truncated and, therefore, incorrect biography of Stanley Zocholl was published. We publish the correct biography for Mr. Zocholl here. Stanley Zocholl (LF’95) received the B.S. and M.S. degrees in electrical engineering from Drexel University, Philadelphia, PA, in 1958 and 1973, respectively. He joined Schweitzer Enginering Laboratories in 1991 in the position of Distinguished Engineer. He was with ABB Power T&D Company Allentown (formerly ITE, Gould, BBC) since 1947, where he held various engineering positions, including Director of Protection Technology. He holds over a dozen patents associated with power system protection using solid state and microprocessor technology and is the author of numerous IEEE and protective relay conference papers. Mr. Zocholl is an IEEE Life Fellow and a member of the IEEE Power Engineering and Industry Applications Societies. He is also a member of the Power System Relaying Committee and past chair of the Relay Input Sources Subcommittee. His biography appears in Who’s Who in America. He received the Best Paper Award of the 1988 Petroleum and Chemical Industry Conference and the Power System Relay Committee’s Distinguished Service Award in 1991.