Implementing Backup with Battery Technology
By Mohamed Fourati, Saft
As the demand for renewable energy increases, and the patterns for supply and demand change, smart digital substations are beginning to be implemented. Electricity transmission and distribution network operators are preparing to equip power substations with digital control and communication carried by fiber optic networks. This will allow faster communication, enhanced safety and more.
It’s important while implementing digital primary and secondary substation equipment to consider the essential role of the backup battery.
Battery systems can be found in every substation and can provide minutes to hours of backup power during a power outage. They can provide power for switchgear to change the configuration of the network, help isolate lines and clear faults before power can be restored safely. They also can power communication and control equipment, which is fast becoming more important in smart digital substations.
By adopting a battery technology that is compatible with digital control and communication, operators can better integrate their essential backup.
French transmission system operator RTE’s Smart Substations project
RTE (RÃ©seau de transport d´Ã©lectricitÃ©), operates 100,000 kilometers of overhead lines ranging from 63,000 volts to 400,000 volts in France, as well as 46 cross-border lines. It is an important electricity network operator in Europe and has implemented battery technology compatible with digital control and communication in its Smart Substations project.
Electricity generation in France has traditionally relied on nuclear power stations. In the past few year, however, there has been a dramatic increase in the use of renewable energy-including wind and solar photovoltaic. There has been progress toward reaching the European Union (EU) targets for renewable energy. Today, 20 percent of French electricity consumption is generated from renewables, including 11,200 MW from wind and 6,600 MW from solar energy. Although this shows progress, France’s objective is to increase the amount to 32 percent by 2030.
To help reach these targets, RTE delivered the four-year Smart Substations project between 2013 and 2016 by creating modern substations that are remote control capable. RTE selected two substations in the Somme region of northern France, where the highest level of grid-connected wind power lies. One was the 90/20 kV Alleux substation, located at the point of supply to distribution system operator ERDF, and the other is the 255/ 90 KV Blocaux substation, located at the interconnection with neighbouring Luxembourg.
When choosing the batteries, RTE had a number of priorities. It needed to ensure the same high levels of performance and safety for the battery systems as other substation equipment.
Its objectives were:
- Minimize the need for on-site supervision and intervention by technicians
- Enabling access to control centers
- Deliver a technology that would remain compatible in the future (in case of the need for extension/alteration)
One additional challenge for backup batteries in a digital substation is that they are harder to integrate with the state-of-the-art SCADA and condition monitoring, which is the raison d’Ãªtre for digital substation technology. Conventional lead-acid battery technology is not immediately compatible with digital communication systems.
RTE selected Saft for its lithium-ion (Li-ion) technology, which could meet the technical requirements, and because it had experience and expertise in utility applications. In addition, because the Smart Substation project is partly funded by the French government and the Blocaux substation is connected to neighbouring Luxembourg, it was important for RTE to consider European and French suppliers when it came to specifying a backup battery system.
The Reasons Behind Li-ion
The main advantage of Li-ion technology is its high energy density, which provides batteries with a compact footprint and reduced weight. This is why Li-ion technology is commonly used in industries where weight and performance are the main priorities, such as aerospace and telecom installations.
Saft’s Li-ion technology dates back to the early 1990s, when it developed its first Li-ion batteries for applications such as mobility, space and defense. Nowadays, Li-ion batteries can be found in consumer devices and electric vehicles as a result of the technology becoming more accessible.
The small size and light weight advantages of Li-ion batteries are not always important in terms of substations or even digital substations and most of RTE’s substations are equipped with lead-acid batteries.
Yet, these were major advantages of Li-ion batteries during the project. One of RTE’s digital substations was located inside an existing building and the other was a containerised solution. This meant that size was an important factor for RTE to consider, and Li-ion technology posed the best option as a result. The smaller the equipment, the easier it is to fit inside a containerised substation or compact substation and the lower the requirements for civil engineering. The fact that Li-ion technology is also lightweight means that less structural support is needed and there is simpler manual handling during installation and maintenance.
Low maintenance was also important to RTE as they wanted an autonomous substation with a minimal number of visits by maintenance technicians to top up or check electrolyte levels. One of the key benefits of the Li-ion batteries is that they are sealed for life so require no maintenance.
The batteries are also modular in nature, meaning that a battery system can be built which is closely aligned with the system requirements. In the case of the Blocaux substation, the battery has been designed to deliver 11 kW at 110 V for up to four hours.
IEC 61850 smart grid protocol
In digital substations, it is important to integrate the substation equipment with the international standard that governs protection and control systems in the grid, known as the IEC 61850.
When it comes to digital communication, a great advantage of Li-ion when compared to other battery technologies is that it requires an electronic battery management system (BMS). This means that it is amenable to integrating into an operator’s SCADA (Supervisory Control and Data Acquisition) system.
Saft achieved this by integrating smart grid communications into the battery charger. The charger is controlled by the battery and it is the interface that relays information to RTE’s smart grid control and protection scheme, using the IEC61850 protocol. It allows RTE to benefit from the same condition monitoring and real-time situational awareness on its batteries as it does from the primary and secondary substation equipment.
Safety is another vital factor in battery selection and Saft has demonstrated the safety of its qualified industrial battery systems through achieving safety certifications in the aviation, space and marine industries (where safety rises above all other factors). For RTE’s project in particular, Saft worked extremely closely with its engineers to demonstrate the safety that is built in our Li-ion technology.
Mohamed Fourati is Saft’s Sales Manager for France and Total & Benning Key Account Manager. He supports backup batteries for critical applications in utilities, oil & gas, buildings and industries customers. With an engineering degree from the prestigious Ã‰cole Nationale SupÃ©rieure d’Arts et MÃ©tiers, he has since worked in a number of technical and commercial roles.”
French transmission system operator RTE has adopted Li-ion battery technology for backup power in its smart substations project. Mohamed Fourati, Saft’s Sales Manager for Stationary Batteries in France, explains the advantages of lithium-ion (Li-ion) battery technology and why it has a growing role in digital substations.