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Analysis of new relays for the detection of islanding of distributed synchronous generators

Grant number: 06/03031-0
Support type:Scholarships in Brazil - Scientific Initiation
Effective date (Start): September 01, 2006
Effective date (End): August 31, 2007
Field of knowledge:Engineering - Electrical Engineering
Principal Investigator:José Carlos de Melo Vieira Júnior
Grantee:Daniel Queiroz Vasconcelos Cunha
Home Institution: Faculdade de Engenharia Elétrica e de Computação (FEEC). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil

Abstract

Distributed synchronous generators connected to distribution systems are prone to operate isolated from the main utility system after contingencies. This fact is known as islanding and it occurs when a portion of the distribution network is disconnected from the utility, yet remains energized by one or more distributed generators connected to it. Utilities requirements and technical guides recommend instantaneous disconnections of distributed generators as soon as an islanding condition occurs. Typically, the disconnection time is smaller than 2 seconds. The most employed devices used for anti-islanding protection are the frequency-based relays (under/over frequency, rate of change of frequency and vector surge relays) and the under/over voltage relay. Nevertheless, these relays may fail if the levels of active and reactive power imbalances of the islanded system are small. Therefore, this research project aims to investigate new relays for islanding detection of synchronous generators. The relays investigated are the rate of change of generator active power (dP/dt), the rate of change of generator active power in relation to the rate of change of the electrical frequency (dP/dt) and the rate of change of terminal voltage in relation to the rate of change of frequency or vice-versa (dV/df or df/dV). The investigation will be done through a set of curves relating the relay trigger times to the active/reactive power imbalance and through the concept of critical power imbalance. These curves will be obtained using non-linear three-phase dynamical simulation and different load-generation profiles. (AU)