Vector surge

Electric Power Systems Research 77 (2007) 170–180

Characteristics of vector surge relays for distributed synchronous generator protection
Walmir Freitas a,∗ , Wilsun Xu b , Zhenyu Huang c , Jose C.M. Vieira a
a b

Department of Electrical Energy Systems, State University of Campinas, 13083-852 Campinas, Sao Paulo, Brazil Department of Electrical and Computer Engineering, University ofAlberta, Edmonton, Alta., Canada T6G 2V4 c Energy Science and Technology Division, Pacific Northwest National Laboratory, 99352 Richland, WA, USA Received 12 September 2005; received in revised form 17 February 2006; accepted 17 February 2006 Available online 17 April 2006

Abstract This work presents a detailed investigation on the performance characteristics of vector surge relays used to detectislanding of distributed synchronous generators. A detection time versus active power imbalance curve is proposed to evaluate the relay performance. Computer simulations are used to obtain the performance curves. The concept of critical active power imbalance is introduced based on these curves. Main factors affecting the performance of the relays are analyzed. The factors investigated arevoltage-dependent loads, load power factor, inertia constant of the generator, generator excitation system control mode, feeder length and R/X ratio as well as multi-distributed generators. The results are a useful guideline to evaluate the effectiveness of anti-island schemes based on vector surge relays for distributed generation applications. © 2006 Elsevier B.V. All rights reserved.
Keywords:Distributed generation; Islanding detection; Synchronous generators; Vector surge relays; Vector shift relays

1. Introduction Distributed generation has recently gained a lot of momentum in the power industry due to market deregulation, technological advances, governmental incentives and environment impact concerns [1–3]. An important requirement for the connection of synchronous generators todistribution networks is the protection system capability of islanding detection. Islanding occurs when a portion of the distribution system becomes electrically isolated from the remainder of the power system, yet continues to be energized by distributed generators. This is also known as loss of mains or loss of grid [3]. Failure to trip islanded generators can lead to a number of problems to thegenerator and the connected loads. The current industry practice is to disconnect all distributed generators immediately after the occurrence of islands [4,5]. Typically, a distributed generator should be disconnected within 200–400 ms after loss of main supply. In order to achieve such a goal, each distributed synchronous generator must be equipped with an islanding detection device. The

∗Corresponding author. Tel.: +55 19 37883740; fax: +55 19 32891395. E-mail address: walmir@dsee.fee.unicamp.br (W. Freitas).

common devices used for this purpose are the modified versions of the under/over voltage and under/over frequency relays. Among them, devices based on variations of frequency have been recognized as the most reliable option by the industry so far. Representative examples of suchrelays are the rate of change of frequency relay (ROCOF) and the vector surge relay (VSR), which is also known as vector shift or voltage jump relay [1–3]. However, it has been well recognized that such relays tend to fail when the mismatch or imbalance between the generation and the load in the islanded system is small. As more and more distributed generators are added to utility systems, it hasbecome clear that a good understanding on the operating characteristics of these relays is important. The results can be very useful for utility engineers to evaluate the reliability and robustness of a given distributed generation anti-islanding scheme. The objective of this paper is to present our investigation results on this subject. The concepts of detection time versus active power...