Power System Operation

photo: generator maintenance work
Scheduled generator maintenance work at
Glen Canyon Dam

Reclamation and Western Area Power Administration (Western) work together on a daily basis in scheduling water releases, developing generation schedules, and coordinating maintenance outages. Western transmits and dispatches power generation from each Reclamation facility and ensures compliance with minimum and maximum flow requirements and other constraints set by Reclamation in consultation with other federal, state, and local entities. In generating and dispatching power, Reclamation and Western must also consider their responsibilities associated with North American Electric Reliability Council (NERC) and Western Electricity Coordinating Council (WECC) criteria. WECC, as a regional council of the NERC, has responsibility for coordinating and promoting electric system reliability in the provinces of Alberta and British Columbia, the northern portion of Baja California, Mexico, and all or portions of the 14 Western states in between.

NERC and WECC operating criteria require Western and Reclamation to meet scheduled load changes by ramping the generators up or down beginning at 10 minutes before the hour and ending at 10 minutes after the hour.  Ramping is the change in the water release from the reservoir through the turbine to meet the electrical load (or power demand). Both scheduled and unscheduled ramping are crucial in load following, ancillary services, power system regulation, emergency situations, and variations in real time (what actually happens compared to what was scheduled) operations. 
Typically, power demand increases during the daylight hours as residences, commercial establishments, agriculture and industry put electricity to use. Hydropower generation can react instantaneously to the load – a pattern called load following. By comparison, coal and nuclear based resources have a relatively slow response time; consequently, they generally have limited load following capability in the WECC.

photo: generator gallery at Glen Canyon Dam
Power generators at Glen Canyon Dam

As a control area operator, Western regulates the transmission system within a prescribed geographic area.  Western is required to react to moment-by-moment changes in electrical demand within this area, adjusting the electrical power output of hydroelectric generators within the area in response to changes in the generation and transmission system to maintain the scheduled level of generation in accordance with prescribed NERC criteria. Automatic Generation Control (AGC) is a process whereby the control system automates the water releases in a manner that follows the power system’s actual dynamic demands on a moment-to-moment (typically a four-second-interval) basis.

In regulating the transmission system, Western needs to be able to ramp releases up or down quickly in response to system conditions. In addition, each utility is required to have sufficient generating capacity – in varying forms of readiness – to continue serving its customer load, even if the utility loses all or part of its own largest generating unit or largest capacity transmission line.  This reserve capacity ensures electrical service reliability and an uninterrupted power supply.
Reserve generating capacity that is connected to the transmission system is called spinning reserve.  Spinning reserves are used to quickly replace lost electrical generation resulting from a forced outage, such as the sudden loss of a major transmission line or generating unit. Additional off-line generating units are also used to replace generation shortages, but they cannot replace lost generation capacity as quickly as spinning reserves.

Last Updated: 2/23/17