Thursday 31 January 2008
Market Outcomes: The Queensland region experienced an energy price of $4994.95/MWh at dispatch interval (DI) ending 11:35 hrs and $885.10/MWh at trading interval ending 12:00hrs. Energy and Frequency Control Ancillary Service (FCAS) prices in other NEM regions were not affected.
Approximately $57,000 of negative settlement residues were accrued on the Queensland to NSW directional interconnector at TI 12:00hrs. The interconnector flow was not counter price for the relevant dispatch interval, however the average flow for the trading interval was in the southerly direction, counter to the half-hour spot price differential between Queensland and NSW.
The fluctuations in Queensland energy prices and QNI interconnector flows caused prices at DI 11:40hrs to be triggered as “subject to review”. The prices were accepted as no manifestly incorrect input was identified.
Principal Contributors: The Queensland demand was just above the ‘knee’ point of the regional supply offer curve for DI 11:35hrs ie a minimal change in the demand of the Queensland region caused a significant change in prices. Support from NSW on QNI was limited to 5MW due to the action of a constraint equation to avoid voltage collapse for the loss of the Kogan Creek unit and the Terranora interconnector was limited to 44MW due to a Directlink cable outage.
Market Performance: Outcomes appear to be consistent with the dispatch offers and power system conditions during the event.
Wednesday 30 January 2008
Market Outcomes: The Queensland energy prices fluctuated between a maximum of $9,920.99/MWh at TI 16:30 and a minimum price of -$308.24/MWh at TI 18:00 on 30 January 2008. Frequency Control Ancillary Service (FCAS) maximum prices in the Queensland region during the event were $1049.76/MWh for the lower 6-second service, and $1050.82/MWh for the lower 5-minute service. Energy and FCAS prices in other NEM regions were not affected.
Approximately $4.2M of negative settlement residues were accumulated on the Queensland to NSW interconnector on the day. Constraint equations were applied to manage negative settlement residues but were ineffective to the extent that they conflicted with the power system security requirements.
The fluctuations in Queensland energy prices and QNI interconnector flows caused prices at DIs 16:05, 16:45 and 17:35 to be triggered as “subject to review”. The prices were accepted as no manifestly incorrect input was identified.
Principal Contributors: The simultaneous trip of both Braemar to Tarong 8814 and 8815 275kV transmission lines was classified as a credible contingency from DI 16:00 to DI 17:30 due to lightning in the vicinity. This reduced the secure supply from south-west Queensland generators (Millmerran, Braemar and Kogan Creek) and QNI to the Queensland loads. During the same period, some of the northern and central Queensland generators were constrained off to maintain the central to south Queensland stability limit. The simultaneous trip of the Bulli Creek to Dumaresq 8L and 8M 330kV transmission lines were classified as a credible contingency from DI 17:10 to DI 19:05, due to lightning in the vicinity. This restriction contributed to the negative energy price being set for TI 18:00.
Some Queensland generators shifted their generation capacity significantly during the reclassification period. This resulted in the dispatch interval price fluctuations rather than uniformly high prices.
Market Performance: Outcomes appear to be consistent with the dispatch offers and power system conditions during the event. Power system security was maintained throughout the event.
Saturday 26 January 2008
Market Outcomes: The Victorian region saw a negative energy price of -$134.09/MWh at trading interval (TI) ending 10:30hrs and the Snowy region saw a high energy price of $5099.50/MWh at TI 13:00. The energy and FCAS prices in other regions were not affected. The Snowy CSP/CSC scheme operated in TI 13:00 hrs to fund approximately $4.4M of negative settlement residues on the Snowy-Victoria interconnector from positive settlement residues on NSW-Snowy interconnector.
Principal Contributors: A planned outage of the Geelong to Keilor No.2 220kV transmission line took place from 6:15hrs to 13:30hrs. Victoria experienced a negative price of -$894.21/MWh at dispatch interval ending (DI) 10:15 when there was a 337MW increase on the Snowy to Victoria interconnector dispatched flow driven by a reduction in the Geelong to Keilor No.1 dynamic line rating and the constraint equation for the planned outage.
For DIs 12:40 to DI 12:50, the energy price in the Snowy region was $9,999/MWh with the Tumut to Murray constraint binding. Approximately 410MW of Snowy generation capacity at Murray was shifted from the lower priced bands to bands priced at more than $7,000/MWh. The Snowy region prices returned to typical values when the Geelong to Keilor No.1 dynamic line rating became less restrictive and expensive Murray capacity offer was no longer required for dispatch.
It is likely that violation of the Geelong to Keilor constraint equations would have been avoided if the Anglesea generator had been in service or if the temperature in Victoria had been less than 30 degrees.
Market Performance: Outcomes appear to be consistent with the dispatch offers and power system conditions during the event. Constraint equations related to the planned outage of the Geelong to Keilor No.2 line were violated between DI 12:10 and DI 12:50. The line was recalled at 12:21hrs. A Victorian smelter load was made available for tripping if required to manage any overloads occurring before the line was returned to service at 13:30hrs. Power system operation during this period is being reviewed against secure limits.
Thursday 10 January 2008
Market Outcomes: From DI 14:05 to DI 17:30 hrs the SA regional reference price was $9,999.72/MWh. Dispatch prices for the Snowy and Victorian regions spiked to $8,176 and $7600.76 at DI 15:55 hrs. The Cumulative Price for the South Australian region stands at $137,500 after this event. Counter-price flows occurred on both the Snowy-Vic and Snowy-NSW directional interconnectors during this period.
Principal Contributors: 30-minute total demand in the South Australian region reached 2,919 MW, driven by temperatures in Adelaide of up to 41 degrees. The Victorian demand 30-minute total demand was 9,266MW with a Melbourne temperature of 40 degrees. Torrens Island power station offered 890MW of its 1160MW capacity at more than $9,900/MWh. The counter-price flows stemmed from a binding system normal transmission constraint between Tumut and Murray in the Snowy region. NEMMCO did not intervene to clamp interconnector flows as the Snowy CSP/CSC arrangements operate to cancel material negative settlement residues that would otherwise accrue.
Market Performance: Outcomes appear to be consistent with the dispatch offers and power system conditions during the event period. The occurrence of counter-price flow simultaneously on both sides of the Snowy region is unusual. It can be understood in terms of nodal pricing in conjunction with loop flows and will be irrelevant when the Snowy region is abolished on 1 July.
Monday 7 January 2008
Market Outcomes: For DIs 14:15 and DI 14:20 hrs the QLD regional reference price was $10,000/MWh, and the spot price for trading interval ending 14:30 was $3,396.26/MWh. Prices in other regions were not affected.
Principal Contributors: A transmission limitation due to an unplanned outage of the No.2 275/110kV transformer at Palmwoods substation in QLD. Approximately 170MW of generation capacity was re-offered from low-priced to high-priced bands just prior to DI 14:15 and 300MW was re-offered to from high-priced to low-priced bands just after DI 14:20. Total regional demand for the half-hour ending 14:30 was 7977MW in Queensland, the highest for the day.
Market Performance: Outcomes appear to be consistent with the dispatch offers and power system conditions during the event period. The transformer outage constraint equation was reviewed and replaced after the event. Although the constraint equation was found to be overly conservative, its application and replacement was found to be in accordance with procedures.
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