An historic step towards the integration of the Texas and Mexico power grids was taken on October 10 with the official opening of the Sharyland high voltage direct current interconnection.

Engineered by ABB, Sharyland is the first large-scale asynchronous interconnection to support both emergency power exchange and commercial energy trading between the United States and Mexico and the growing economies of the Rio Grande Valley.

The $40 million HVDC back-to-back tie connects the state power grid of Texas and the national power grid of Mexico, operated by Electric Reliability Council of Texas (ERCOT) and Comision Federal de Electricidad (CFE) respectively.

 

Click to enlarge The Sharyland back-to-back tie interconnects the Mexican and U.S. 138 kV AC grids by converting AC electricity to DC at one converter in the station, and sending it as DC to the other converter in the station where it is reconverted to AC. The process operates in either direction, and allows electricity from two separate power networks to move back and forth efficiently across the border on the Rio Grande. The tie is at a point near the cities of Mission, Texas, and Reynosa, Tamaulipas.

ABB was selected by Sharyland Utilities in 2005 to create a HVDC tie connecting power grids in Texas and Mexico. The interconnection strengthens both grids by allowing them to transfer power to each other as needed. It enables 150 megawatts of power to be transferred in either direction and allows each grid to support the other during peak demand and grid emergencies. It is also equipped with short-term overload capacity in excess of its continuous rating of 150 MW.

It is an essential installation, because even though the American and Mexican power networks have the same fundamental power frequencies (60 Hz), they operate independently and thus could have different frequency and voltage variations. An AC link could create severe operational difficulties, such as uncontrolled power flow and power swings leading to grid collapse. The power moving in either direction must be synchronized with the power network it is moving into, which is what Sharyland's power converters do.

As an open-access tie, Sharyland allows CFE and any energy provider in ERCOT to use the facility for commercial energy transactions between the two countries.

With strengthened grid reliability a customer priority, ABB designed a HVDC solution that includes a unique black start emergency assistance capability that provides a safe supply of power during a blackout in either AC grid. The solution also acts as a firewall that isolates disturbances and prevents them spreading from one grid to the other.

The solution is equipped with ABB's MACH 2 control and protection system, which is designed specifically for converters in power applications. MACH 2 is the highest performance and most used control and protection system for HVDC and FACTS (flexible AC transmission systems) on the market, with more than 400 installations in operation worldwide.

BB was selected by Sharyland Utilities in September 2005 for its technically and economically superior solution and its long and successful track record in executing complex HVDC projects over many decades.

Benefits * Energy trading - open to any power supplier in ERCOT and Mexico * Helps stabilize both grids through active and reactive power variation * Emergency support - immediate transfer of power in the event of supply/demand imbalances * Black Start capability - safe supply of power during blackouts * Firewall function - prevents disturbances from spreading between grids * Unmanned operation - designed to operate remotely from a dispatch center in the ERCOT grid