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TC2 - Technical requirements for network protection

Protection must respond to both utility grid and Microgrid faults. If the fault is on the utility grid, the desired response may be to isolate the Microgrid from the main utility as rapidly as necessary to protect the Microgrid loads. The decision point for isolation is dependent on the specific customer's loads on the Microgrid. In some cases sag compensation can be used without separation from the distribution system to protect critical loads (ex. examine how long Microgrid can support the utility grid). If the fault is within the Microgrid, the protection coordinator isolates the smallest possible section of the radial feeder to eliminate the fault. In order to cope with the bi-directional energy flow due to large numbers of DG new protection schemes are required. Protection is always a tradeoff between the desired level of security and its costs. As vast protection equipment on the low voltage level will not be economical, the capabilities of the local generators and loads with regard to their sensors and communication have to be exploited.

In this task the following will be investigated:

• ABB will review and re-evaluate the network protection paradigm to suit Microgrid operation, and will examine modern protection devices, such as fault current limiters, self-adjusting protection devices etc.
• ISET and SMA will study the enhancement of the central electronic switch developed in the Microgrids-project by latest impedance measurement techniques with low and additional monitoring and communication capabilities. ABB will also study different operational aspects of the central solid switch (ex. time of islanding, reconnection, etc.).
• ISET will investigate novel protection schemes using real-time data of the medium voltage level and offline data of the energy management systems of the Microgrids. They will be self-adjusting with regard to the Microgrid configuration, loads and generation. Tests will be carried out in the DeMoTec laboratory with an intelligent protection device. This is connected to the medium voltage level and interconnected via ethernet with the Microgrids' EMS.
• Possible increased fault levels can be another symptom of directly coupled DG. Many generators will contribute to faults and may push the system fault level past the duties of switchgear. Replacing switchgear is a costly task. ABB will study the possibility of avoiding this cost through the use of advanced protection.
• ICCS/NTUA and Manchester will revisit the earthing requirements for the network, the sources and the consumer premises to ensure the safety of operation in either mode (grid-tied and isolated). Manchester will evaluate the effect on network regulating means, such as the load tap changers of transformers, and will propose new requirements and control strategies.
• EMforce will investigate the development of low-cost electronic protection devices particularly suited for LV networks with low fault levels.
• ZIV will study the possibilities of performing the required coordinated behaviour of the whole system in the case of faults in various locations and specifically will identify the opportunities to share data between local generator/load units and network protections in order to allow for an optimal operation of the system, clearing selectively during the incidents or the faults, as well as allowing the proper sequences for the restoration of the normal service conditions.