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Intelligent Protection

Local network security in the age of microgrids and distributed generation.

Fortnightly Magazine - July 2014
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Investments in distributed generation (DG) and microgrids are widely reported to be in growth mode. Electricity customers and communities alike have been quick to embrace these new opportunities, and have turned to DG and microgrids to seek supply reliability solutions and other benefits. The economic benefits of DG are realized by combinations of reducing energy costs for consumers, improving supply reliability and also by deferring investment in transmission and distribution systems as a result of its proximity to load centers. Furthermore, emission reductions make a compelling argument for higher penetration of DG.

Yet these higher levels of grid-connected microgrids also bring new challenges for the safe operation of the distribution network. That's because DG operators will continue to value the power supplied from the larger grid to which they remain connected - even as they prepare to operate independently by islanding DG systems from the grid on occasions when it is favorable to do so.

One practical challenge faced by all stakeholders, regardless of where they stand on the ongoing DG and microgrid debate, is ensuring that utility and customer assets, employees and community members remain safe and protected throughout all modes of grid-connected DG and microgrid operation. This protection requirement is fundamental, even as new technologies and operating modes are adopted and as new regulations and standards struggle to keep up with this rapid technical innovation.

Figure 1 - Fault at bus 3 location and relay under reach at circuit breaker CB1

While IEEE 1547 standards provide some guidance for proper integration of DG, protective relaying systems continue to be an issue, and traditional protection schemes, in consideration with unidirectional power flow static system configuration, are of major concern. With an increase in DG integration, planners will deal with complex distribution systems where bidirectional power flow and dynamic system configuration will become the norm. With this new paradigm, the protection system will require a re-evaluation.

In fact, protection and control engineers on the front lines are struggling to keep this increasingly dynamic infrastructure safe and operable. And it's already apparent that their focus will shift away from protecting a traditional static unidirectional network and towards a bidirectional dynamic network. Adaptive protection is one approach, adapting and responding to dynamic system conditions and utilizing decision logic.

"Fire and Forget" Won't Work

The utility distribution systems serving independent-minded DG customers and communities are typically designed to supply a predominantly one-directional power flow that brings the upstream-generated supply down to serve customer load demands. These radial architecture networks are well-defined, stable and well-protected using traditional breaker, fuse, and recloser components with fixed and static configuration designs and settings. This static configuration "fire and forget" design premise will safeguard a network of low complexity. It offers a low-cost, highly effective, and highly reliable protection solution - one that

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