Latest Thinking

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  Low Voltage Network Protection Utility Workshop- Summary and Next Steps

  Increased penetration of Distributed Energy Resources and microgrids have fundamentally changed the operational characteristics of Low Voltage (LV) network systems. Current LV network protection philosophy and practice are due for a significant revamp to keep up with changing operating conditions. This workshop invites four of the major LV network users in the US to discuss the challenges they face today and the new technologies they have been experimenting with. In light of this workshop discussion, use cases for further hardware-in-the-loop testing efforts are proposed to evaluate new LV network protection solutions.

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  Roadmap for Advancement of Low-Voltage Secondary Distribution Network Protection

  Downtown low-voltage (LV) distribution networks are generally protected with network protectors that detect faults by restricting reverse power flow out of the network. This creates protection challenges for protecting the system as new smart grid technologies and distributed generation are installed. This report summarizes well-established methods for the control and protection of LV secondary network systems and spot networks, including operating features of network relays. Some current challenges and findings are presented from interviews with three utilities, PHI PEPCO, Oncor Energy Delivery, and Consolidated Edison Company of New York. Opportunities for technical exploration are presented with an assessment of the importance or value and the difficulty or cost. Finally, this leads to some recommendations for research to improve protection in secondary networks.

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  Overview of the Impact of Renewables on Distribution Protection and Control

  Traditionally, distribution circuits have been designed with substations providing power to dispersed customer loads. The substation transformer is typically Delta-connected on the high voltage side and Wye-grounded on the low voltage side to distribution feeders. Since the power flows in one direction from the substation to the customer, the protection system typically consists of phase and ground overcurrent relays, fuses, and feeder reclosers. Fuse curves and overcurrent relay curves are selected to ensure protection coordination, assuming that the fault current is uni-directional from the substation. Additionally, load break sectionalizers may be utilized in conjunction with reclosers to reduce the area impacted by a fault on the feeder. The distribution system voltage is controlled by load tap changers (LTCs), capacitor banks, and/or voltage regulators (VRs). The algorithms used to control these devices can be as simple as time-based control assuming that the load current flows from the substation to loads. With the integration of DERs into the electric grid, these conventional schemes for distribution feeder protection and control are challenged.

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