A contingency event is an event affecting the power system that AEMO expects would likely involve the failure or removal from operational service of one or more generating units and/or transmission elements.
AEMO is responsible for determining which SWIS events are classified as Credible Contingency Events. This is described in WEM Procedure: Credible Contingency Events.
Credible Contingency Events
A Credible Contingency Event is an event that AEMO expects would likely involve:
- the failure or removal from operational service of one or more energy producing units, Facilities and/or Network elements; or
- an unplanned change in load, Intermittent Generation or other elements of the SWIS not controlled by AEMO
There are two broad classes of Credible Contingency Events:
- Single Power System Element
AEMO considers the failure of any single Power System Element as reasonably possible, except for Nodes because the failure of Nodes is negligible under normal operating conditions.
AEMO has classified Power System Elements into simplified functional groups as shown in the following table.
|Element||Description||Example physical equipment (non-exhaustive)|
|Node||Electrically equivalent location||Substation busbar|
|Circuit||Single electrical connection between two or more nodes.||Overhead transmission line, underground cable, transformer.|
|Single terminal device||Auxiliary network equipment connected to a node.||Shunt reactor / capacitor, static VAR compensator.|
|Protection Scheme||Scheme that detects an electrical fault and disconnects any other Power System Element to prevent damage.||Special Protection Scheme designed to disconnect a generator under certain fault conditions.|
|Communications link||Means or path for information flow between nodes.||Fibre-optic cable, microwave transmitter.|
|Measurement device or sensor||Source of information about power system conditions.||Current transformer, voltage transformer, weather sensor (e.g. temperature, wind speed, solar radiation).|
|Generation or load system||Producer or consumer of electrical power.||Gas-fired generator, transmission connected load, rooftop photovoltaic system.|
An example of a single power system element contingency event is the loss of KW-SF 82.
KW-SF 82 is the designation for the 132 kV transmission circuit 2 connecting Kwinana and South Fremantle substations.
This Contingency Event covers the loss of the KW-SF 82 circuit for reasons such as:
- A lightning strike on or near the line
- A tree branch falling across the line conductors
In either of these situation, the circuit protection operates to isolate the circuit.
- Multiple Power System Element
Multiple Power System Element events that impact more than one single power system elements simultaneously.
An example of a multiple power system element contingency event is the activation of the Mid-West Area Reinforcement Network (MARNET) Scheme. The activation of that scheme will result in the following occurrences:
- Loss of transmission elements:
- YDT-ENT 91
- Loss of generation facilities:
- Load shedding at KARARA
Non-Credible Contingency Events
Non-credible contingency events are contingency events other than credible contingency events. AEMO considers these events have a low probability of occurrence, such as busbar contingencies or multiple transmission elements tripping at the same time.
AEMO may reclassify Non-credible Contingency Events as Credible Contingency Events when there is an increase likelihood of the event occurring. This may be likely during site work or extreme weather conditions such as bushfires or storms. AEMO will conduct an assessment on the likelihood of the contingent event based on the operating conditions before initiating the reclassification.
Publication of Events
In accordance with clause 3.8A.6(a) of the WEM Rules, AEMO must publish any new Credible Contingency Event or reclassification of a Non-credible Contingency Event on its website. The data will be available at the WEM Market Data page: http://data.wa.aemo.com.au/#dispatch-advisory