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Glossary - o

For your convenience, this page contains an alphabetically organized list of terms, definitions and common acronyms used in the electric utility industry.

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Term/Acronym

Definition
O&M Operations and Maintenance
OCN Operating Condition Notice
OOM Out of Merit Order
OOMC Out of Merit Capacity
OOME Out of Merit Energy
Obligation Total Obligations scheduled by a QSE that are comprised of energy Obligations and Ancillary Services Obligations where:
  • Energy Obligations =
    Load + losses + energy sales + energy exports; and
  • Ancillary Services Obligations =
    ERCOT allocated Ancillary Services Obligations (which may be self-arranged) + Ancillary Services sales (to ERCOT or to other QSEs)
Off-line The status of Resources that are not synchronously interconnected to the ERCOT System.
Oklaunion Exemption The export schedules from the Public Service Company of Oklahoma, the Oklahoma Municipal Power Authority, and the AEP Texas North Company for their share of the Oklaunion Resource over the North DC Tie that are not treated as Load connected at transmission voltage, are not subject to any of the fees described in Section 4.4.4, DC Tie Schedules, and are limited to the actual net output of the Oklaunion Resource.
On-line The status of a Resource that is synchronously interconnected to the ERCOT System.
On-Peak Hours Hours ending in 0700 to 2200 CPT from Monday through Friday excluding NERC holidays.
Operating Condition Notice The first of four possible levels of communication issued by ERCOT in anticipation of a possible emergency condition detailed in Section 5.6, Emergency and Short Supply Operation.
Operating Condition Notice (OCN) The first of four possible levels of communication issued by ERCOT in anticipation of a possible emergency condition detailed in Section 6.5.9.1 Emergency and Short Supply Operation.
Operating Day The day, including hours ending 0100 to 2400, during which energy flows.
Operating Guides Guidelines approved by the ERCOT Board describing the reliability standards for ERCOT.
Operating Hour A full clock hour during which energy flows.
Operating Period A two-hour period comprised of the Operating Hour and the hour preceding the Operating Hour.
Operating Plan A plan developed by ERCOT to operate the ERCOT System in Real Time.
Operational Constraint Anticipated or actual security violation or overload of a transmission element, based on actual network topology.
Operational Model The transmission model based on actual network topology of the ERCOT System.
Opportunity Outage See Outage
Out of Merit Capacity Capacity provided by a Resource selected by ERCOT outside the bidding process to resolve a reliability or security event.
Out of Merit Energy Energy provided by a Resource selected by ERCOT outside the bidding process to resolve a reliability or security event.
Out of Merit Order (OOM) The selection of Resources for Ancillary Services that would otherwise not be selected to operate because of their place (or absence) in the bidding process for that service.
Outage The condition of a facility that has been removed from service to perform maintenance, construction, or repair on the facility.

Forced Outage
An Outage initiated by protective relay, or manually in response to an observation by personnel that the condition of equipment could lead to an event, or potential event, that poses a threat to people, equipment, or public safety.

Maintenance Outage
An Outage initiated manually to remove equipment from service to perform work on components that could be postponed briefly but that is required to prevent a potential Forced Outage and that cannot be postponed until the next Planned Outage. Maintenance Outages are classified as follows:
  1. Level 1 Maintenance Outage – Equipment that must be removed from service within 24 hours to prevent a potential Forced Outage;
  2. Level II Maintenance Outage – Equipment that must be removed from service within seven days to prevent a potential Forced Outage; and
  3. Level III Maintenance Outage – Equipment that must be removed from service within 30 days to prevent a potential Forced Outage.
Opportunity Outage
An Outage that may be accepted by ERCOT when a specific Resource is Off-Line due to an Outage.

Planned Outage
An Outage that is planned and scheduled in advance with ERCOT, other than a Maintenance Outage or Opportunity Outage.

Simple Transmission Outage
A Planned Outage or Maintenance Outage of any Transmission Element in the Network Operations Model such that when the Transmission Element is removed from its normal service, absent a Forced Outage of other Transmission Elements, the Outage does not cause a topology change in the LMP calculation and thus cannot cause any LMPs to change with or without the Transmission Element that is suffering the Outage.
Outage Scheduler The application that TSPs or QSEs use to submit Notification of Outages or requests for Outages to ERCOT for approval, acceptance, or rejection.
Output Schedule The self-scheduled output for every five-minute interval of a Resource provided by a QSE before the execution of SCED.