Protection schemes used in North American microgrids

Abstract

Summary This study reviewed existing conventional and nonconventional protection schemes for grid‐connected and islanded mode operations in North American microgrid projects. The microgrid projects investigated in this study used different types of distributed energy resources (DERs) and integrated hydropower/diesel generators, gas/steam/wind turbines, and photovoltaic systems with energy storage. In this work, conventional protection schemes were defined as those within the IEEE Standard C37.2‐2008, whereas nonconventional schemes were those not defined within this standard. The pros and cons of conventional and nonconventional protection schemes were discussed in detail. The overvoltage, undervoltage, and frequency elements were the most common conventional protection schemes applied in microgrid projects in North America. These protection elements were used to detect the islanded conditions and faults that could not be sensed by overcurrent relays because of small fault currents contributed by low‐inertia DERs and power‐electronic sources. Directional overcurrent elements were used to distinguish between external (grid) and internal (microgrid) faults. Adaptive protection was the most popular nonconventional protection scheme applied to the microgrid projects. In conclusion, different types of DERs and operational modes must be considered in order to address the protection and control challenges of each microgrid and to obtain the best technical and economical solution.

Assessment of the Phase-to-Ground Fault Apparent Admittance Method with Phase/Ground Boundaries to Detect Types of Electrical Faults for Protective Relays Using Signature Library and Simulated Events

“…In the grid simulation event mode, part of the 12.47 kV Riverside-EPB of Chattanooga utility grid 13 -was simulated with MATLAB/ Simulink software. e single-line diagram of the power grid circuit is shown in Figure 3, and this network configuration was a radial power system (7.2 kV phase-to-ground voltage) that was fed by a three-phase source with a Wye-ground configuration (Riverside substation).…”

“…In Figure 4, the results were collected as MATLAB files. IntelliRupters were used in the 12.47 kV Riverside-EPB of Chattanooga utility grid [13]. However, an inverse time overcurrent relay with…”

“…e detection of the faulted phases to observe the types of electrical faults could be performed by measuring the overcurrent magnitudes at each phase because current magnitudes usually increase at fault states. In electrical fault scenarios at microgrids, with the power grid connected or islanded to hydropower sources (high spinning inertia cases), overcurrent relays could detect the faulted phases; however, the faulted phases could not be sensed by overcurrent relays in microgrids with small diesel generators, wind turbines, and photovoltaic (PV) panels without energy storage systems (low spinning inertia cases), because of the small electrical fault currents contributed by the low inertia of distributed energy sources [13]. In addition, the most common electrical faults such as the phase to ground could be detected by measuring the voltage magnitudes, which usually decrease at faulted phases along the power line sections [14].…”

Outdoor Test Bed Performance of a Power Line Sensor Using a Real-Time Event Simulator

“…In Figure 9, the power line sections were simulated with a three-phase π section line block. IntelliRupters are used in the 12.47 kV Riverside EPB utility grid [8], but an inverse time overcurrent relay MATLAB/Simulink model [23] was used on this study. The ratio of the CTs for the relay's breaker was 400/5 A.…”

“…Additionally, the global use of solar and wind power has grown rapidly, with accelerating growth in recent years [7] such that the use of inverter-based distributed energy resources has increased along with electronic solid-state switches to control microgrid systems [8]. These devices could provide highharmonic components into the microgrids that could affect the power quality and grid reliability [9].…”