Microgrid protection

Microgrid protection

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Power-system protection encompasses the interrelated concerns of assurance of human safety, mitigation of equipment damage and provisions for reliable transmission and distribution of electrical power to end users. For conventional power delivery systems-from national power grids to household electrical distribution- the design methods and engineering design solutions for protection have benefited from over a century of experience. However, as renewable energy penetration into the grid is increasing, long-held practices for protective system design and associated hardware and controls are proving to be inadequate. This is particularly the case for microgrids. The microgrid has emerged as an efficient means for introduction of locally supplied renewable energy source(s) (RESs), such as solar photovoltaic (PV) and wind, and a diversity of local generation sources, such as national gas generation, into existing grid structures. With the inclusion of energy storage systems (ESSs), the microgrid provides a means for improving grid resiliency and achieving truly energy secure systems. Throughout this chapter, distributed generation (DG) or distributed generators (DGs) refers to any distributed source of power, including RESs or more conventional natural gas generators and back-up supply diesel generators. The term distributed energy resource (DER) refers generally to DGs and ESSs. The inclusion of ESS is implied by the use of the term DER, whereas DG or DGs refer only to power generation. The microgrid concept effectively integrates and manages simultaneously generation, energy storage and load demand. The microgrid also provides a viable means for electrification of energy poor areas. Although technically not a microgrid, electrified transportation power-distribution systems share many common traits with microgrids. From the beginning, the achievement of accurate fault discrimination within a microgrid has been an issue. In the case of AC microgrids, this protection challenge has not prohibited implementations because the microgrid can be integrated into existing protective structures, albeit with suboptimal behavior during fault events.

Chapter Contents:

  • 12.1 Protective system design objectives
  • 12.2 Conventional protective system design practice
  • 12.2.1 Fault characterization
  • 12.2.2 Protective equipment and scheme components
  • 12.2.3 Fault coordination analysis and protective relaying
  • Overcurrent relays
  • Directional overcurrent relays
  • Differential relays
  • Under/overvoltage/frequency protection
  • 12.3 Microgrid protection challenges
  • 12.3.1 Impact of distributed energy resources on power flow
  • 12.3.2 Impact of distributed energy resources on fault current magnitude
  • 12.3.3 Impact of microgrid connection modes and changing configurations
  • 12.3.4 Earthing considerations
  • TN, TT and IT systems
  • Line-to-ground faults in radial LVac microgrid
  • 12.3.5 Cyberattacks
  • 12.4 Promising solutions for microgrid protection
  • 12.4.1 Limiting maximum DER capacity
  • 12.4.2 Evolving communication standards
  • 12.4.3 Fault current limiters
  • 12.4.4 Utilization of the ESS for fault discrimination
  • 12.4.5 Distributed generation control modifications
  • 12.4.6 Protective system design process for microgrids
  • Data analytics, feature extraction and behavior classification
  • Adaptive protection
  • 12.4.7 Addressing cybersecurity
  • 12.5 DC microgrid considerations
  • 12.5.1 DC fault characteristics
  • Stage 1: capacitor discharge stage (natural response of DC-side RLC circuit)
  • Stage 2: AC-side current feeding stage (forced response)
  • Diode freewheeling stage (natural response of DC-side inductive circuit)
  • 12.5.2 DC protective system approaches
  • 12.5.3 DC protective devices
  • Fuse
  • Mechanical circuit breaker
  • Solid-state circuit breaker
  • Hybrid circuit breaker
  • 12.5.4 DC system grounding
  • 12.6 Conclusion: future of microgrid protection
  • References

Inspec keywords: power grids; power generation protection; energy storage; distributed power generation; renewable energy sources

Other keywords: engineering design solutions; household electrical distribution; locally supplied renewable energy source; power-system protection; microgrid concept; distributed generators; supply diesel generators; natural gas generators; reliable transmission; protective system design; grid structures; microgrid protection; renewable energy penetration; protective structures; grid resiliency; energy secure systems; energy poor areas; design methods; conventional power delivery systems; distributed energy resource; electrical power; electrified transportation power-distribution systems; protection challenge; AC microgrids; national gas generation; energy storage systems; local generation sources; national power grids; power generation

Subjects: Power system protection; Distributed power generation; Energy resources

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