Portable power solutions: Flexible all-rounders
Does a power plant need to be connected to the grid quickly? Or is there a grid fault that needs bypassing? Portable power solutions like mobile substations or E-houses are attractive for both emerging and industrialized countries. They provide the greatest possible flexibility up to extremely high voltage levels and ensure a safe grid operation.
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The dust cloud from the convoy is visible from afar. Its destination: a substation in the north of the Saudi Arabian capital of Riyadh. A defective high-voltage system has caused a power failure. Tens of thousands of households are without power. Weeks may pass before the severe fault can be corrected, and expensive emergency power systems would be required to ensure the power supply of the grid. An employee of the grid operator, National Grid SA, a subsidiary of the Saudi Electricity Company, is relying on a different solution this time: The power failure will be bypassed with a mobile substation and reconnect the affected grid. The six trailers on the way to Riyadh include everything National Grid SA needs for this solution: gas-insulated switchgear, transformers and all necessary auxiliaries, including control and protection systems. The power system bypass is in place within just a few days. The lights stay on in Riyadh – thanks to a financially and ecologically sound solution.
Applications such as this are becoming increasingly important for scheduled or unscheduled power failures in Saudi Arabia. In the summer of 2018, the country will get two extremely high-capacity mobile substations from Siemens – most probably the highest-capacity systems of their type worldwide. The two mobile high-voltage switchgear systems will certainly have the highest capacity in a single feeder configuration Siemens Energy has constructed to date. The mobile switchgear systems are truly impressive, with a capacity of up to 502 megavolt-amperes (MVA). They are also designed for a rated voltage of up to 420 kilovolts (kV). “There is only one other competitor in the sector besides us who produces mobile switchgear at this voltage level,” says Dr. Alexander Rentschler, head of Product Lifecycle Management at Siemens Energy Power Portable Solutions in France, “Thanks to their flexibility the systems can be integrated in any section of the grid.”
" The mobile substations will allow us to bypass any 380 kV substation in the event of failure or major maintenance work. "M. Ali S. Al-Rammah, head of Service at National Grid SA
Bridging different voltage levels
Why does Saudi Arabia need this high technology from Europe? Between 1971 and 2013, power consumption in the kingdom increased more than 26 times over to 8,741 kilowatt-hours per person.1 The country thus ranks among the top 20 consumers worldwide and uses roughly three times as much electric power as the global average.2 Like every country, Saudi Arabia also wants to minimize any losses due to power failures or maintenance and to increase the robustness and reliability of its grid. This is no easy task, especially as the heterogeneous energy landscape of Saudi Arabia operates with different high voltage levels. On January 17, 2017, Khalid Al-Falih, Saudi Arabian Minister of Energy, Industry, and Mineral Resources, described the nation’s program for promoting renewable energy and emphasized that the Kingdom seeks to produce 9.5 gigawatts of renewable energy in 2023. This will further increase the need for flexible solutions.
" It has been essential for us to specify and acquire a customized plug-and-play solution that we could quickly mobilize and install on our own. "M. Ali S. Al-Rammah, head of Service at National Grid SA
Quickly connecting power plants to the grid
In the future, the portable solution will enable National Grid SA to connect the kingdom's backbone 380 kV grid with any of the three other grid voltage levels (132,115 and 110 kV). “The National Grid SA-specified mobile substations configuration jointly customized with Siemens, will allow us to bypass any 380 kV substation in the event of failure or major maintenance work,” states Ali S. Al-Rammah, Vice President of National Grid SA and head of the company’s maintenance business line. “They can also be used as fast-track solutions to connect a new plant to the grid. It has been essential to develop a customized technical specification for us to have a plug-and-play solution that we could quickly mobilize and install on our own. It will significantly improve the high voltage grid resiliency that is the backbone of our power transmission infrastructure.”
So just connect it to the grid and it's done?
Easy to install
“That's right,” says Rentschler. “The modular systems are each mounted on six specially designed trailers. These modules are pulled by trucks to the deployment site at 40 to 50 kilometers per hour. Once they arrive, they only have to be connected together. The modules include all the key components: Power transformers, gas-insulated switchgear, cables, protection and control systems and auxiliary power supply. They are connected to the grid by overhead lines or cables. The trick: All components are prefabricated and fully factory-tested before delivery. The customer can thus independently install and commission the mobile substation within a few days, with no help from Siemens personnel.”
Record-setting capacity in a compact package
The two substations to be delivered to Saudi Arabia each contain three single-phase autotransformers, each with a capacity of 167.3 MVA. “These are therefore the largest transformers Siemens has ever built for mobile substations, and are probably the highest-capacity ones worldwide,” Rentschler says. Together with the gas-insulated switchgear (GIS), these form the heart of the system.
But sheer size and power are not always best. The greater the capacity and voltages, the larger the physical systems become and the more difficult it is to fit them in the limited space on a trailer. The Siemens Energy developers and engineers had an inspiration: The HV bushings for the GIS systems and for the transformers can be rotated, and are folded down to save space during transport. Once the trailer is stationary, the HV bushings can be gradually deployed to the overhead power lines. National Grid SA can thus transport the substation very safely in compact modules.
Rough roads? No problem.
Substations are sometimes in use twelve months per year. That’s why they need to be sufficiently rugged to withstand dusty, bumpy roads, sandy winds and temperatures of over 55° Celsius. To minimize mechanical stresses on the pressure systems during transport, Siemens Energy developed from single components (GIS, its enclosure and the trailer) one single structural system with special interfaces. The clever anchoring system in the trailer gives the GIS enough freedom of movement during transport. Rentschler notes: “Just a few millimeters are critical for safe transport.”
Wide range of applications
But the demand for mobile solutions doesn't stop with grid operators and electric power utilities. Around the world energy-intensive industry sectors such as oil and gas, metals, mining and chemicals rely on the portable energy highway to keep outages as short as possible. There are even environmental benefits, according to Rentschler. Mobile switchgear systems can be removed without a trace. Mobility is becoming an important topic for power systems, due in part to the increased input of electric power from renewable sources. There are now even mobile power plants.
Sometimes mobile solutions become the permanent solution. For example, the power demand is growing much faster than the grid in some countries in Africa, so Siemens Energy delivered more than 40 mobile substations to Algeria over the last ten years, and the majority of them will remain several years in operation at the same place. “Such a fleet allows the grid operator to build a substation with very short notice in critical areas of the grid. However, tailor made preassembled substations such as 'E-Houses' already shorten installation time by up to 30 percent over conventional systems,” explains Rentschler. “This enables the grid to be expanded, or to connect a critical plant in a fast track mode.”
1 World Bank, Electric power consumption (kWh per capita), IEA Statistics © OECD/IEA 2014
2 World Bank, Data Catalog, Table 5.11, World development indicators: power and communications, electric power, consumption per capita, world: 3.104 kWh per capita
Nov 02, 2017
Picture credits: Siemens