Feeding Energy to the Grid

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This photo shows a power distribution panel (PDP) on the right and a pad mount transformer (PMT) on the left from our Lewiston, MN, wind project. These are critical pieces of high voltage electrical equipment that are used at each turbine. Power enters this PDP through cables passing through an underground vault in the turbine foundation. The PMT “steps-up” the power from the turbine generators to 34.5 kilovolts (kV) at this site and it is then sent through underground cables to the project substation several hundred yards away where it is transformed again to grid level voltage for consumption. If you look closely, you can see the other turbine at this site in the distance behind the PDP. Since the PDP and PMT are needed for each turbine they are usually included in the scope of equipment supply by the manufacturer. The project owner / operator should make arrangements to test and maintain this equipment when planning for operations. It is typically not maintained by the interconnecting utility.

The photo on the right shows the substation at our Lewiston, MN, project site where the power from each of the two turbines is “stepped-up” again through the main transformer to 69 kV for use on the local grid. The substation contains an array of equipment such as capacitors, relays, metering equipment, switches, and lightning protection systems to name a few. The main transformer is the large box –shaped object in the center of the photo. Because this project interconnects with transmission lines, this substation needed to be constructed and is our responsibility to maintain.

Substations are made to last decades and are fairly robust  but proper inspection and regular preventative maintenance are recommended. When planning the interconnection of a project to the local grid you may have the ability to connect to distribution lines which are smaller and sometimes less costly than large transmission infrastructure. This may depend on a number of factors such as project size, distribution capacity near the project’s location and the power sales arrangement if you choose to negotiate an agreement for sale to the local utility. In many cases, if the local utility is purchasing the power from the project, the substation may continue to be owned and maintained by the utility and save the project that responsibility. However, substation upgrade costs and annual maintenance payments to the utility may still be expensive. These factors vary by project but should be considered when looking at interconnection options and project economics.

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