A Novel Single-Ended Transient-Based Boundary Protection Scheme for 35 kV Active Distribution Networks Based on Capacitive Voltage Transformers

When many distributed generators (DGs) are connected to active distribution networks (ADNs), the performance of conventional overcurrent protection can seriously deteriorate. In response, single-ended transient-based boundary protection is considered an effective scheme for improving relay performance in ADNs due to its independence from power supply properties and its ability to cover an entire protected feeder. However, this approach depends on the filtering effect of the line boundary. This paper finds that capacitive voltage transformers (CVTs), metal-oxide arresters (MOAs), and the stray capacitances of the other apparatuses can serve together as line boundaries at substations and switching stations, and their excellent high-frequency filtering characteristics can assist in boundary protection design. A protection criterion is constructed based on the differences in high-frequency spectral energy between the internal and external fault-generated traveling waves (TWs). Furthermore, a novel two-stage boundary protection scheme is formed by reasonably coordinating the operation sequence and the protection scope of the first- and second-stage boundary protection. Finally, based on the PSCAD platform, the effectiveness, sensitivity, and reliability of the proposed protection scheme are verified under different fault scenarios.

I. Introduction

As an effective and important means to alleviate energy shortages and address environmental pollution, the penetration degree of distributed generators (DGs) in distribution network systems is increasing daily [1], [2], [3]. This irreversible trend has led to a transformation from traditional radial distribution networks to scattered multisource active distribution networks (ADNs) [4]. Moreover, the fault characteristics of ADNs, including uncertain power flow directions, limited fault current amplitudes, and fault level differences between grid-connected and islanded modes, have become extremely complicated [5], [6], [7]. These issues have contributed to the deterioration of the performance of conventional overcurrent protection [8], creating enormous challenges in effectively protecting ADNs.