Thursday, 15 September 2011
Market Outcomes: South Australia experienced an energy price of $2113.27 for trading interval (TI) ending 1000hrs.
FCAS prices for South Australia and FCAS and energy prices for the other NEM regions were not affected by this event.
Prior to the incident, the Parafield-Gardens West 275 kV line in South Australia and the Kerang-Redcliffs 220kV line in Victoria were out of service for scheduled work. Constraint equations to manage these outages limited generation at Pelican Point Power Station and into Victoria on Murraylink.
Principal Contributors: A rebid received at 0918 hrs for Torrens Island Power Station offered 330 MW of generation capacity in bands priced at more than $11000 per MWh from dispatch interval (DI) ending 0935 hrs. During this DI the 5-minute price for South Australia reached $12497.52 per MWh. At the time, the Kerang-Redcliffs outage constraint equation limited flow into South Australia on Murraylink to 83 MW.
Prices returned to normal levels following a decrease in demand in South Australia.
Market Performance: Outcomes appear to be consistent with the dispatch offers and power system conditions during the event.
Monday, 12 September 2011
Market Outcomes: South Australia recorded energy prices of $3800.96 per MWh and $1910.01 per MWh for the trading intervals (TIs) ending 0030 hrs and 0730 hrs on Monday 12 September 2011.
Frequency Control Ancillary Services (FCAS) prices for South Australia and FCAS and energy prices for the other NEM regions were not affected.
Principal Contributors: South Australia had wind generation of less than 100 MW during the affected TIs. During dispatch intervals (DIs) ending 0010 hrs and 0015 hrs a binding South Australia voltage stability constraint equation limited interconnector flow from Victoria to South Australia to approximately 600 MW. The 5-minute prices for South Australia reached $11200.70 per MWh when high-priced generation offers were cleared for 2 DIs. During this period three generating units in South Australia were declared as non-conforming (refer to Market Notices 36044-36046). Prices returned to normal when one of these units moved to its dispatch target, which coincided with a decrease in demand.
The Kerang-Red Cliffs 220 kV line was scheduled to be removed from service at 0648 hrs. The associated outage constraint equation limited the flow on Murraylink towards South Australia to 39 MW during DIs 0700 hrs and 0705 hrs. South Australian prices reached $11264.72 per MWh during DI 0705 hrs due to a slight increase in demand. Prices returned to normal levels when an additional 413 MW of generation was offered at negative prices.
Market Performance: Outcomes appear to be consistent with the dispatch offers and power system conditions during the event.
Monday, 5 September 2011
Market Outcomes: Queensland experienced an energy price of $2116.93 per MWh for Trading Interval (TI) ending 1100 hrs.
Lower FCAS prices (sum of all Lower Services) for Queensland reached $6777.30 per MWh and $13581.06 per MWh for TIs ending 1100 and 1130 hrs respectively. FCAS prices and energy prices for the other NEM regions were not affected by this event.
Principal Contributors: 5-Minute prices in Queensland reach the Market Price Cap of $12500 per MWh for dispatch interval (DI) ending 1055hrs when incorrect dynamic line ratings were used in the constraint equations managing the loadings on the Calvale-Wurdong 871 and Calvale-Stanwell 855 275 kV transmission lines. An incorrect emergency rating for the 871 line and the continuous rating for the 855 line were used by the central dispatch process, following a Powerlink database update.
The change in the Queensland to New South Wales interconnector flow for DI ending 1055 hrs was below the 80 MW threshold and so the price for that interval was not revised despite the incorrect input.
In DIs 1055 hrs and 1110 hrs, the target flow on the Queensland to New South Wales interconnectors increased from 212 MW to 333 MW when almost 4000 MW of generation capacity in Queensland was offered at negative prices for DI 1110 hrs, up from 2839 MW for DI 1055 hrs when the high price occurred. The rebidding, combined with a decrease in Queensland demand that coincided with the high energy price, resulted in 5-minute prices reaching $0.00 per MWh for DI ending 1115 hrs.
The increased southward flow also resulted in high FCAS prices (Lower services) for DIs 1100 to 1110 hrs, since the Armidale-Dumaresq 8E 330 kV line was out of service from 1002 hrs, and the loss of the parallel no 8C line would result in the separation of Queensland from New South Wales.
DI 1105 hrs was identified as subject to review when the Queensland 5-minute energy price changed from $91.78 per MWh to $5.77 per MWh, and the target flow on the Terranora interconnector reversed towards New South Wales. AEMO determined that DI ending 1105 hrs contained manifestly incorrect inputs (MIIs) and replaced all dispatch prices and market ancillary services prices with the corresponding prices for the last correct dispatch interval (ending 1100 hrs) and used these to determine the spot prices for trading interval ending 1130 hrs.
Market Performance: Although dispatch interval 1055 hrs was affected by a manifestly incorrect input when incorrect dynamic line ratings were used in three constraint equations, AEMO’s automated procedures for determining a manifestly incorrect input were not triggered for this DI.
DI 1105 hrs was subsequently indentified as subject to review and Queensland energy and FCAS prices were rejected.
The trigger thresholds relate to changes in regional energy price and cleared interconnector flows, and are described in AEMOs annual review of price revision triggers “Effectiveness of Procedures for Manifestly Incorrect Inputs”, located at http://www.aemo.com.au/electricityops/140-0104.html.
A Price Revision report describing the event in more detail will be published shortly.
For enquiries regarding these reports, please contact: AEMO's InfoCentre.
