A physical laboratory for protective relay education

Undesirable but unavoidable natural events or human errors will occur to disrupt normal power system operation. Engineers must apply protective relay systems for the most probable events based on practical judgment to minimize service interruptions and damage to the equipment. Understanding the performance and limitations of different protective relay systems is vital in their application. One can explain the philosophy of system protection, the basic theory of a protective relay system, and the relay algorithms from classroom sessions and/or computer simulation. However, it is difficult, if not impossible, to evaluate the actual performance and possible misoperation of a relay in the field just through computer simulation or benchtop testing. This paper introduces the usage of the Power System Simulation Laboratory at the Energy Systems Research Center to enhance the teaching and research activities in relay education. A brief description of the laboratory configuration and the design of the relay testing station are presented. Some sample examples to illustrate the use of this facility for undergraduate and graduate education in protective relay systems are also included in this paper.

I. Introduction

One OF the most challenging tasks for today's power engineers is to ensure a high level of continuity of service to customers even under system disturbances. However, a number of undesirable natural events or human errors may occur to disrupt normal system operation. These events have to be isolated within a local area in a timely fashion to avoid damaging the utility equipment, long interruptions of service to a wide area of customers, and possible personnel hazards. Protective relaying plays an important role in the whole process [1]–[3]. The IEEE defines a relay as “an electric device that is designed to interpret input conditions in a prescribed manner and after specified conditions are met to respond to cause contact operation or similar abrupt change in associate electric control circuits” [4]. Originally, all protective relays were the electromechanical type. They are still being used by many utilities. Solid-state relays were introduced in the 1950s and are commonly used today for their relative accuracy, ease of testing, and maintenance. The concept of using digital computers for protective relay systems was introduced in the 1960s. Over the years, the cost of digital computers has steadily declined; at the same time, their computational power has increased substantially. The cost of the electromechanical relays has increased over the same period. The application of microcomputer-based relays is growing rapidly, and a number of microprocessor-based protective relay systems are applied in utility systems [5]. Regardless of the operation mechanism, the performance of a protective relay is a subject of great concern to utility engineers. Since an almost infinite number of intolerable conditions may occur in the power system, the engineer must apply the protective relay system to the most probable events based on practical judgment. This uncertainty tends to make the design of a protective system an art as well as a technical science. The understanding of the performance and limitations of different protective relay systems becomes vital in the system design and application process.