Safety & Protection Practices of Smart Grid

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By Benjamin Coalson, Amos Ang, and Manuel Avendaño

The interconnection of large numbers of renewable generating plants in remote, environmentally sensitive areas presents challenges to the reliable operation of the power grid. Constructing new transmission infrastructure to mitigate reliability concerns is generally costly, time-consuming, and often not viable due to the environmental constraints. To support a clean energy future, minimize environmental impacts, reduce construction and operation costs, and ensure grid reliability, Southern California Edison (SCE) has implemented the Centralized Remedial Action Scheme (CRAS).

By Md Rukonuzzaman

Thanks to the introduction of feed-in-tariff (FIT) and net-metering system, prosumers have the options either to store the extra power generated by distributed generators to the battery or deliver the extra power to the utility grid when load demand is less than the generating capacity. The sharp fall of the price of Li-ion batteries and long lifetime compared to other energy storage technologies have further increased the popularity of battery storage based distributed generators among the household and small-scale industrial consumers. HESS based distributed generators ensure reliable and uninterruptible power supply during the power outage and even when PV based distributed generators are not available. Distributed power generation and storage in household consumers involve bidirectional battery inverter and PV inverter in two separate units or hybrid inverter (PV inverter plus bi-directional battery inverter) in a single unit, and sophisticated white goods like refrigerator, washing machine, and microwave oven. Stringent measures need to be taken into consideration while designing the energy storage system as integrated with distributed generators to protect household electrical and electronic equipment from damage, and prosumers and maintenance personnel from hazardous electrical shock.

By Vilayanur Viswanathan, Matthew Paiss

The total heat released and rate of heat generation by Li-ion batteries during abuse spans a wide range, with forced ignition of off-gases releasing up to 20 times rated energy when subjected to external heating. This article summarizes the results of short circuit, crush, overcharge and external heating for li-ion batteries with nickel based layered oxides (NLO) and lithium iron phosphate (LFP) cathodes. The need for standardized safety testing with quantifiable metrics is highlighted in the current product safety standard UL9540. The total heat generated is proportional to ampere-hour capacity, while peak heat generation rate increases exponentially with specific energy. The 2.5X higher specific energy of NLO-based cells, relative instability of layered cathodes, and higher operating voltage make them more susceptible to thermal runaway.

By G. Pradeep Reddy, Y. V. Pavan Kumar

The modern smart grid initiatives support interoperability of local/onsite micro-power grids which are normally located in vicinity of each other as opposed to the macro-power grids. Hence, effective communication technologies play a very crucial role in collecting data and transferring control centre decisions for desired operation from the grid management view. Figure 1 shows several wireless technologies used in smart grid development [1]. Among these, LPWAN (Low-Power Wide-Area Network) are suitable for interoperability of local micro-power grids since the information exchange is typically in the order of few bytes. The LPWAN is a wide-area wireless communication network typically meant for long range communications with low data rate and low power consumption. This article describes a few key technologies used for LPWAN such as Sigfox, Narrowband-Internet of Things (NB-IoT) and LoRa (Long Range). These new technologies can be used to establish an effective communication between micro or macro power grids which operate on different bandwidths and at different distances.

By Amin Yazdaninejadi, Sajjad Golshannavaz, Farrokh Aminifar

Realizing sustainable electrification process requires design and implementation of robust protection schemes. In one classification, the distribution network- or microgrid-wide protection strategies enabled by inelegant electronic devices (IEDs) (also known as GPS-connected smart relays or micro phasor measurement units (Micro PMUs) falls under a centralized structure around the phasor data concentrator (PDC). However, the recently developed relay-to-relay communication-based protection scheme shows more promise due to its distributed nature (see Fig .1). In the centralized structure, relays capture synchronous data frames and frequently report the calculated phasor values and its derivatives to the PDC. The data is then refined and handed to the distribution network or microgrid monitoring, protection, and control (MPAC) center for making the final decision. It is evident that, in the case of any failure in the infrastructures of centralized approach, protection system functionality is seriously imperiled resulting in a widespread outage. In the relay-to-relay communication scheme, smart relays share essential data with each other in a given protection zone (PZ), namely immediate neighbors, to discover faulty branches. Based on predefined logics, they reach a consensus on the protection decision of the faulty branch and main/backup relays in charge. The data sharing mechanism of this strategy assures protection scheme robustness and enhances electrification process suitability in smart grids hosting distributed energy resources (DERs) [1].


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