Wind and the Transmission System

Using the Electric Transmission System for Wind Generation

All users of the electric transmission system must follow “good engineering practices” in order to connect and use the system. These practices include following established criteria regarding equipment that is connected to the system as well as operating the system reliably when transmitting electrical power from the source (generator) to the load (electricity users). Much of these criteria were developed following past electrical system blackouts – the most notorious of which was the 1965 Northeast Blackout that affected the New York and New England area. This blackout resulted in the establishment of the National Electric Reliability Council, now known as the North America Electric Reliability Council (NERC).

In Minnesota, the Mid-Continent Area Power Pool (MAPP) supervises the connection of new equipment and the use of the transmission network. MAPP committees, made of representatives from member companies, review proposed connections and determine whether or not they meet established criteria.

An electric utility is required to adhere to criteria when connecting new equipment – whether it is owned by the electric utility or a third party such as a wind generation developer. Federal Energy Regulatory Commission (FERC) rules require electric utilities to treat all electric transmission users in a comparable manner, including other utilities and non-utility users of the transmission system such as wind generation.

Two Components of Transmission Use

Before any new generation can be connected to the transmission system, two separate studies must be completed: a System Impact Study to review the direct electrical interconnection and a Transmission Service Request Study to review the use of the electric transmission network between the generator and the load.

In order to monitor the connection and approval process, each transmission utility must maintain queues to keep track of requests for system connections and transmission service. Before a study can be started, a request must be entered into the queue – either the generator queue for the System Impact Study or the appropriate OASIS (Open Access Same-time Information System) for the Transmission Service Request. Entries can be made in both queues simultaneously.

The wind generation developer is responsible for the costs of performing these studies, which must be made available to the public after they are completed. Generally, these studies are posted on company websites or on the MAPP website.

System Impact Study

The System Impact Study (SIS) report contains information about the electrical interconnection and how it is used. The electrical interconnection consists of the physical equipment such as wires, switches, transformers, meters, etc. The type and design of the equipment must meet the criteria. This is important both for the protection of the party connecting to the electric system as well as the other transmission users.

The SIS report also analyzes whether the appropriate equipment is being used and whether it can withstand the maximum short-circuits and current flow at the connection point. The impact that the new generation has on nearby electrical equipment (adjacent substations) also is reviewed. In some cases, equipment at the adjacent substation may have to be replaced and this cost would be included in the report.

Preparing the SIS report can take months or years depending on the size and complexity of the generation equipment that will be connected. The study must include the impacts of all generators that have a higher queue ranking. A SIS report for wind generators of 2 MW to 20 MW typically takes about three months to prepare. Completion of the SIS report does not guarantee that the new connection will be accepted since it may take some time for additional transmission equipment to be installed.

After the SIS report is completed, it must be reviewed and approved by the transmission owner and receive approval from the MAPP Design Review Subcommittee. This MAPP committee approval takes a least one month but may take longer if the report must be modified.

Transmission Service Request

A Transmission Service Request (TSR) study must be approved before a wind generator can use the electric transmission system. This study evaluates the impact of sending power from the generator to the load. Due to the parallel flow nature of the electric transmission system, restrictions (criteria violations) that prevent a TSR study from being approved may not be near the generator or the load. Transmission service cannot be granted until the restrictions are removed, usually by upgrading or expanding a transmission system.

Transmission owners are obligated to upgrade their system to accommodate the transmission service request within their capability to do so. This process involves planning for upgrading existing facilities or constructing new facilities, acquiring regulatory permits and receiving approval by various MAPP transmission committees. In some cases, the transmission owner may not receive all necessary approvals and cannot provide the transmission service.

The owner of the new wind generator may have to pay the costs of upgrading or installing new equipment.

The Connection Process – Who to Contact?

Contact the local electric supplier to determine which utility owns a transmission line. Each transmission owner may have a slightly different process for reviewing transmission connections.

Transmission line owners must provide a good faith effort to accommodate generation connection requests. For more information about connecting to Great River Energy’s transmission system, contact wind@grenergy.com or call 763-241-2447.

Each transmission owner has a person you can contact to obtain a copy of the contract(s) regarding the System Impact Study and deposits required to initiate the study. They can also provide a list of information required (proposed one-line diagram, contact persons, equipment data, etc.) for a new generator.