Mackinac - Back-to-Back Converter Station

The Mackinac HVDC project is a significant electrical infrastructure development in Michigan, USA, designed to enhance grid stability and control power flow between the Upper and Lower Peninsulas. This project features a 200 MW back-to-back VSC HVDC converter station supplied by Hitachi Energy to the American Transmission Company (ATC).

Technical Specifications

The Mackinac HVDC converter station is rated to transfer up to 200 megawatts of power bidirectionally and provide reactive power for local voltage support within milliseconds under extremely dynamic conditions. It operates at a nominal voltage of ±160 kV. The station is situated near the Straits Substation, in line with a pre-existing 138 kV AC cable double circuit across the Straits of Mackinac.

Technology

The Mackinac project utilizes Voltage Source Converter (VSC) technology, which was selected over classic HVDC technology for several reasons:

It supports all islanded operation under certain conditions. It provides excellent voltage and reactive power control for wind generation. It can stabilize extremely weak power networks. It has black-start capability, allowing it to restart a grid after a blackout.

This project is notable for being the world's first large-scale back-to-back HVDC system using multilevel VSC technology.

Purpose and Benefits

The Mackinac HVDC installation serves several important purposes:

It acts as a buffer to slow down and redirect large amounts of electrical power, preventing the regional network from being overwhelmed. It enhances grid stability and reliability through power flow control. It supports the integration of more renewable energy sources, particularly wind power, into the energy mix. It allows for maintenance and upgrades of the existing transmission infrastructure by enabling the scheduling of outages.

Construction and Components

The construction of the Mackinac HVDC Converter Station included hot-dipped galvanized structural steel, precast concrete divider walls and floors, and insulated metal wall panels. The station consists of two converters, designed so that during maintenance of one converter, the other can run as a STATCOM, continuing to provide dynamic voltage support to the network.

System Integration

The Mackinac HVDC project is integrated into a complex electrical system. It connects the transmission systems in the Upper Peninsula (UP) and northern Lower Peninsula of Michigan, which are linked through submarine cables across the Straits of Mackinac. This connection is important for managing the increased electricity flow from west to east across the Upper Peninsula, particularly with the addition of new power sources such as wind farms.

Technical Advantages

The VSC HVDC technology used in the Mackinac project offers several technical advantages:

It can operate under minimal short circuit levels. It can control power flow regardless of system changes. It provides fast and independent control of active and reactive power.

These capabilities make the Mackinac HVDC system particularly well-suited for managing the challenges of the Michigan power grid, including the integration of renewable energy sources and the need to stabilize weak power networks.

The Mackinac HVDC project offers a flexible and efficient solution to the unique challenges of Michigan's electrical grid. Its implementation has improved system stability, facilitated the integration of renewable energy sources, and enhanced the overall reliability of power transmission between Michigan's Upper and Lower Peninsulas.