AC Microgrid Protection System Design Challenges—A Practical Experience

Abstract

Alternating current (AC) microgrids are the next step in the evolution of the electricity distribution systems. They can operate in a grid-tied or island mode. Depending on the services they are designed to offer, their grid-tied or island modes could have several sub-operational states and or topological configurations. Short-circuit current levels and protection requirements between different microgrid modes and configurations can vary significantly. Designing a microgrid’s protection system, therefore, requires a thorough understanding of all microgrid operational modes, configurations, transitional states, and how transitions between those modes are managed. As part of the microgrid protection design, speed and reliability of information flow between the microprocessor-based relays and the microgrid controller, including during microgrid failure modes, must be considered. Furthermore, utility protection practices and customer requirements are not always inclusive of the protection schemes that are unique to microgrids. These and other aspects contribute to the overall complexity and challenge of designing effective microgrid protection systems. Following a review of microgrid protection system design challenges, this paper discusses a few real-world experiences, based on the authors’ own engineering, design, and field experience, in using several approaches to address microgrid protection system design, engineering, and implementation challenges.

Microgrid Protection Challenges and Mitigation Approaches–A Comprehensive Review

“…A can be seen in Figure 22, the three-phase fault happened at Bus 1, and assume that Z T 1 is the impedance of feeder 1, Z Grid is the impedance of the utility grid and V T h is the voltage at fault. The total fault current contribution by utility grid in absence of DER is given as equation ( 8) and Z T h of the network during fault in the absence of DER at feeder 2 can be calculated as equation (9).…”

“…Different types of protection schemes were proposed in the literature to tackle these protection issues. Some of the protection schemes from literature, such as in article [9], authors expressed real-world experiences related to the microgrid design for protection systems, field experience, and implementation challenges. A comprehensive review is available in an article [10], for hybrid AC/DC microgrid protection.…”

“…The main objective of a microgrid is to supply continuous and reliable green energy to electricity consumers. Fault current level depends on the power generation sources, load location, and impedance level [9]. These factors change during grid-connected and islanded modes.…”

Intelligent Transition Control between Grid-Connected and Standalone Modes of Three-Phase Grid-Integrated Distributed Generation Systems

“…An ideal three-phase voltage source is considered as the main grid with R g and L g components per phase. The major challenge with this configuration is to maintain voltage and frequency at the PCC and coordinate the operation of reclosures and protective relays for safe and quick disconnection of DGs from the utility during the grid-side abnormalities with compliance to the grid standards [25,26]. This operation also involves automatic reconnecting, or intervention of the operator to reclose the DG connection with the grid after the abnormality is cleared.…”

Adaptive Central Control Scheme and Investigation of Fault Current Contribution for Protection of Microgrid

“…Adam H et al, [3] also reviews on various key issues that occur in the MGs. Vegunta et al, [4] also discussed the benefits and techniques to switch between protection setting groups automatically as part of adaptive-protection schemes, to provide microgrid transitions between grid-tied and island modes. Shahzad.U,et al, [5] discussed on various types of protection issues and also solutions to some of them in the paper.…”