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Gas-Power Infrastructure: The Missing Link?

Presenting an option to solving electric transmission congestion.
Fortnightly Magazine - February 15 2002

Presenting an option to solving electric transmission congestion.

A recent FERC study of transmission constraints concluded that there are a number of significant electric transmission constraints in the contiguous United States that have the effect of increasing costs of power to consumers. 1 If alleviated, the study concludes that the "benefits in overall energy bills are potentially quite large."

The foundation of existing natural gas pipeline and local distribution company (LDC) systems in the U.S., together with associated expansion investments, can hold a key that provides a viable option to address existing transmission constraints in the power industry. This foundation includes not only the physical assets of the gas pipeline and LDC systems, but also the regulatory, commercial, and operational aspects of those systems. Gas systems can be used to support the development of new generation in power-constrained areas, placing the gas industry in an advantageous position. Gas companies can capitalize on electric restructuring by developing a deeper understanding of the electric grid in their markets and more proactively monitoring the planning process of regional transmission organizations (RTOs).

Power Transmission System Constraints

The power industry is confronted with the issue of developing transmission systems that give it the ability to transport power to the market from the points of actual power generation. Total transfer capability is defined for individual power transmission lines and transmission interfaces. Transmission interfaces usually define the transmission paths between electrical zones within a larger region, or between regions.

Transmission constraints can occur whenever the potential exists for more power to flow over a transmission line or transmission interface than should flow. Limits are set recognizing the transfer capabilities and taking into account the criteria established to ensure reliable operation of the grid. The transfer capability over a transmission line or transmission interface can be based on 1) thermal limits, 2) stability limits, or 3) voltage limits.

Thermal limits are established so that the current level flowing over the transmission facilities does not reach the maximum current-carrying capability of the facilities. Voltage limits are established so that the power flow over transmission facilities does not exceed levels where, given the impedance of the system, voltage levels diminish to unacceptable levels. Stability limits are established to prevent power flows from exceeding limits that would trigger a fault somewhere on the system, resulting in the potential loss of synchronization and the tripping of generators that could lead to system separation. The transfer limit for a particular transmission line or transmission interface is based on which of the three transfer-limiting criteria (thermal, voltage, or stability) is the most limiting under specific system conditions.

Two possible options involving new infrastructure exist in the long term for eliminating the power transmission constraints. One involves new construction of transmission facilities to increase the transfer capability. The second involves the construction of additional generation in zones requiring additional power.

The Gas-Power Vision: Five Obstacles

For the natural gas infrastructure and the available pipeline system capacity to be utilized as a foundation for the reduction in power transmission congestion, there are certain issues that need to be