With use rising, the US electricity transmission and distribution system is susceptible to potential voltage collapse or instability without additional investment in reactive power, the North American Electric Reliability Council (NERC) says in an updated reliability assessment of the nation's bulk electric systems.
Because of its interaction with the transmission system, "reactive support is one area that distribution companies cannot ignore, if reliability is to be maintained on the bulk transmission system," NERC says in its report.
A chief component of that growth�air conditioning�particularly requires it because most air conditioner load is motor load, NERC says. Technically, the physics of transferring power across a transmission line causes it to consume reactive power with increased transfers, resulting in increased voltage drop across the line. NERC says the sources of reactive power include generators, transmission lines, synchronous condensers, capacitors, and specialized reactive support devices.
Under open access, many more transactions are being done across long distances than was ever contemplated when the system was designed and built. In addition, the direction and amount of transfer has become much more volatile, changing daily, sometimes hourly. As a result, planning reactive support for improving transfer capability is now "extremely difficult," NERC says.
Presently, NERC says, no incentives exist to boost reactive support and, in fact, there are real disincentives not to do so since generators are paid to produce real power, not reactive power. Reactive power decreases as real output rises. Business is increasing on the transmission system, but NERC says, little is being done to increase the load serving and transfer capability of the bulk transmission system.
In addition, new flow patterns have led to an increasing use of transmission loading relief (TLR) procedures, including areas not previously subject to overloads, NERC says. NERC TLRs are called by security coordinators to curtail transactions that cause transmission facility overloads or violations of operational security limits.
So far this year, the number of TLR Level 2 and above is up substantially. They rose to about 175 in August, compared to about 76 in August 1999, and about 10 in August 1997. Nonfirm transactions are curtailed at Level 2 and firm at Level 3.
Only 8,455 miles of transmission facility additions�230 kv and higher�are planned throughout North America during the next 10 years, a 4.2% increase in total installed circuit miles. However, the number is up by 1,467 miles over NERC's 1999 projections. But most of the additions are intended to address local transmission concerns and will not have significant impact on long distance power transfers, says NERC.
Four significant transmission projects have been proposed in the Electric Reliability Council of Texas (ERCOT) under a controversial state-mandated cost-sharing formula that is being challenged in state courts. But in most regions there is little agreement on how to pay for new capacity.
NERC says the gap between the need to expand the system and proposed construction is widening. However, a FERC decision to allow alternative methods for determining the allowed return on transmission assets may stimulate additional investment in transmission projects, NERC says.