amendment to standards for Queensland to be applied from 15 July 2000

Reliability Panel
Queensland Frequency Operating Standards in the National Electricity Market
Introduction
Under clause 8.8 of the National Electricity Code (‘the Code’) the Reliability Panel is required to set standards for power system frequency, as part of the power system security and reliability standards.
Standards for Queensland currently have a similar but not identical structure to the standard for the southern interconnected region of the national electricity market. After an alternating current interconnection between Queensland and other regions of the market is fully operational, the standards for all regions will need to be fully aligned, for normal interconnected operation. This will occur with commissioning of QNI and declaration of the interconnection date in accordance with clause 9.36.1 of the Code.
NEMMCO, in conjunction with Powerlink, has recommended a minor amendment to the current standard for Queensland, to apply until the interconnection date. The amendment will introduce a load change level to the standard. This will more closely align standards with other regions. The value of the different frequency levels in the Queensland standard will, however, continue to reflect the smaller electrical size of the Queensland region compared with the southern interconnected regions.
NECA asked the Reliability Panel to consider the recommendation using the timing prescribed for
Code change consultation. On April 14 2000 the Panel released a consultation paper, including
NEMMCO’s recommendation and supporting argument. The formal meeting required by clause
8.8.3(f) was held at the conclusion of the national electricity market forum on April 27 in Brisbane.
This meeting was also video conferenced to Adelaide, Canberra, Melbourne and Sydney.
Views of interested parties
The Reliability Panel received three responses to the consultation paper from CS Energy, Stanwell
Corporation and the Basslink Development Board. All three broadly supported the main recommendations contained in the consultation paper.
The submission from Stanwell Corporation , whilst broadly supporting the amendment questioned the combination of high and low frequency limits within the contingency bands where typically the frequency would only fall for loss of a generator and increase for loss of a load.
CS Energy sought clarification as to whether smelter trips would be treated as load change contingency, their preferred option, or as an other credible contingency.
Basslink Development Board also presented a submission broadly supporting the consultation paper and the Reliability Panel’s intention to consider economic criteria in the standards.
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Consideration of the Reliability Panel
All submissions supported the proposed amendment. In a subsequent discussion with Stanwell it was agreed that the matter raised in relation to the need for upper and lower bounds for situations where frequency would tend to move in only one direction should be addressed by a broader restatement of the overall standard. Although switching of load blocks may cause frequency variations on disconnection or reconnection. The Panel believes it is appropriate to consider this in a more general review as part of a planned review to consider economic criteria in the standards.
NEMMCO confirmed they saw no basis to change from the current practice of classifying smelter trips as load change contingencies for the purposes of the frequency standards.
No other matters of concern were raised in submissions.
In recognition of the forthcoming interconnection of Queensland to the other regions of the national electricity market, the Panel has amended Schedules 1 and 2 so that Schedule 1 shall also apply to
Queensland after the interconnection date.
As noted in the June 1999 determination the time at which an island forms is treated separately from the times before and after island formation. For completeness the discussion presented in the
1999 determination on this matter is included below.
Frequency at the time of formation of an electrical island.
Viable electrical islands can form only when there is sufficient generation technically capable of stable operation to match all or part of the demand within the islanded section of the network. In practice only a very limited number of viable islands can exist in the national market. If a viable island cannot form, supply to all load in that section of the network will be lost.
When an island can form the frequency will depend on the characteristics of generator and customer plant, the level of transfer to/from the islanded area and the ancillary services available and despatched immediately prior to the island’s formation. Thus, if a specified minimum frequency standard is to be maintained, pre-emptive despatch and prior contracting of local ancillary services is required whenever there is a material risk that an island may form even though the network is interconnected. The associated costs can be significantly higher than for other areas either not likely to be islanded or, in an area where a viable island is not likely to be able to form.
Frequency within a viable and stablised island.
Frequency control within a viable and stabilised island will be related to the characteristics of generator plant, customer load and the ancillary services available and despatched in the island. The size of an island has a significant impact on the cost of maintaining a given frequency in the island, in general the smaller the island the more variable the frequency.
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It is not realistic to define a cost-effective standard for all potential islands. However the Panel believes it is appropriate to recognise the position of the relatively few areas of the interconnected network where a viable island may form.
The June 1999 determination noted that this in effect has already been done for the Queensland region (prior to the interconnection date) and is consistent with the expectation of price sensitivity in future standards. The treatment of islands is therefore to be achieved by:
 for the purposes of frequency standards, establishing a common treatment for the time of creation of any island by regarding an event which causes an island to form, eg the interruption to a single interconnector, as if it were a multiple contingency. It is accepted that the frequency under these conditions is likely to deviate from normal by a considerable degree and temporary interruption to load within an islanded area may in some circumstances be necessary to allow a stable island to form. In practice it is also recognised that depending on prevailing conditions the extreme frequency experienced as an island forms, will often not reach the allowable limits, and
 specifying a standard for frequency within specified significant potential viable islands which reflect the size of the island, viz the networks of South Australia as a special case of the general interconnected standard and for Queensland which is covered by a separate schedule prior to the interconnection date and a possible further amendment to apply after that date.
The Panel’s decision
The Reliability Panel determines that the frequency standards for the National Electricity Market shall be
 for New South Wales, the Australian Capital Territory, Victoria and South
Australia - unchanged from the previous determination as detailed in Schedule 1; and
 for the Queensland region prior to the interconnection date - those detailed in Schedule 2, and after the interconnection date - those detailed in Schedule 1.
This determination shall apply from 15 July 2000.
Reliability Panel
July 2000
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Frequency standards for operation of the transmission network of the National Electricity
Market in New South Wales, the Australian Capital Territory, Victoria and South Australia,
(the interconnected network) and Queensland (post interconnection date).
Interconnected operation.
For the electrically connected sections of the interconnected network NEMMCO must use reasonable endeavours to ensure that power system frequency does not move outside the normal frequency band listed in Table 1, except as provided below.
1.
In the event of a large sudden and unplanned change in system load, ensure that power system frequency a) does not move outside the load change contingency band; and b) is restored to within the normal frequency band, in accordance with Table 1.
2.
In the event of the sudden and unplanned disconnection of a generating unit from the interconnected network, ensure that power system frequency: a) does not move outside the single generator contingency band; and b) is restored to within the normal frequency band, in accordance with Table 1.
3.
In the event of the sudden and unplanned occurrence of a single credible contingency other than a large generating unit (as described in item 2 above), ensure that power system frequency: a) does not move outside the (other) credible contingency band; and b) is restored to within the single generator contingency band; and c) is subsequently restored to within the normal frequency band, in accordance with Table 1.
4.
In the event of the sudden, unplanned simultaneous occurrence of multiple contingency events, ensure that power system frequency: a) does not move outside the multiple contingency band; and b) is restored to within the single generator contingency band; and c) is subsequently restored to within the normal frequency band, in accordance with Table 1.
Electrical island formation
For the purposes of this standard any event which may cause a section of the interconnected networks to become disconnected from the remainder (to island), shall be treated in the same manner as a Multiple Contingency condition in table 1 in respect of frequency within the island.
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Electrical island operation
In the event an electrical island forms, the values in table 1 for; the limit of contingency band frequency for the normal band, the load change contingency band and the single generator contingency band shall be the same as that for the (other) credible contingency band in respect of frequency within the island.
In undertaking ancillary service contracting NEMMCO must anticipate the potential formation of an electrical island due to the separation of the South Australian network from the interconnected network.
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Frequency standards for operation of the National Electricity Market in New South Wales, the Australian Capital Territory, Victoria and South Australia and Queensland (post interconnection date).
CONTINGENCY
CONDITION
NORMAL
LOAD CHANGE
DISCONNECTION OF
SINGLE GENERATING
UNIT
CONTINGENCY BAND
NORMAL BAND
LOAD CHANGE
CONTINGENCY BAND
SINGLE GENERATOR
CONTINGENCY BAND
LIMIT OF
CONTINGENCY
BAND
FREQUENCY
(Hz)
49.9–50.1
49.75–50.25
49.5–50.5
ELAPSED TIME TO RESTORE FREQUENCY TO
SINGLE GENERATOR
CONTINGENCY BAND
—
—
—
NORMAL BAND
—
5 minutes
5 minutes
(OTHER) CREDIBLE
CONTINGENCY
(OTHER) CREDIBLE
CONTINGENCY BAND
49.0–51.0
60 seconds 5 minutes
MULTIPLE
CONTINGENCY
MULTIPLE
CONTINGENCY BAND
47.0–52.0
60 seconds 10 minutes
NEMMCO must use reasonable endeavours to maintain System time (expressed in Universal Time, previously known as GMT) within 3 seconds of
Universal Time.
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Frequency standards for operation of the National Electricity Market in Queensland prior to the interconnection date
NEMMCO must use reasonable endeavors to ensure that power system frequency does not move outside the normal frequency band listed in Table 2, except as provided below.
1.
In the event of a large sudden and unplanned change in system load, ensure that power system frequency: a) does not move outside the load change contingency band; and b) is restored to within the normal frequency band, in accordance with Table 2.
2.
In the event of the sudden and unplanned disconnection of a single generating unit from the network, ensure that power system frequency: a) does not move outside the single generator contingency band; and b) is restored to within the normal frequency band, in accordance with Table 2.
3.
In the event of the sudden and unplanned occurrence of a single credible contingency other than a large generating unit (as described in item 2 above), ensure that power system frequency: a) does not move outside the (other) credible contingency band; and b) is restored to within the single generator contingency band; and c) is subsequently restored to within the normal frequency band, in accordance with Table 2.
4.
In the event of the sudden and unplanned simultaneous occurrence of multiple contingency events, ensure that power system frequency: a) does not move outside the multiple contingency band; and b) is restored to within the single generator contingency band; and c) is subsequently restored to within the normal frequency band, in accordance with Table 2.
Electrical island formation
For the purposes of this standard any event which may cause a section of the Queensland network to become disconnected from the remainder (to island), shall be treated in the same manner as a
Multiple Contingency condition in table 2 in respect of frequency within the island.
Electrical island operation
In the event an electrical island has been formed from a section of the Queensland network
NEMMCO shall use reasonable endeavours to maintain the standards listed in Table 2 in respect of frequency within that island.
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Frequency standards for operation of the National Electricity Market in Queensland prior to the interconnection date
CONTINGENCY
CONDITION
NORMAL
LOAD CHANGE
DISCONNECTION OF
SINGLE
GENERATING UNIT
CONTINGENCY
BAND
NORMAL BAND
LOAD CHANGE
CONTINGENCY BAND
SINGLE GENERATOR
CONTINGENCY BAND
LIMIT OF
CONTINGENCY
BAND
FREQUENCY (Hz)
49.85–50.15
48.5–51.0
48.5–51.0
ELAPSED TIME TO RESTORE FREQUENCY TO
SINGLE GENERATOR
CONTINGENCY BAND
—
—
—
NORMAL BAND
—
5 minutes
10 minutes
(OTHER) CREDIBLE
CONTINGENCY
(OTHER) CREDIBLE
CONTINGENCY BAND
48.0 – 51.5 60 seconds 10 minutes
MULTIPLE
CONTINGENCY
MULTIPLE
CONTINGENCY BAND
47.0–52.0
60 seconds 10 minutes
NEMMCO must use reasonable endeavours to maintain System Time (expressed in Universal Time, previously known as GMT) within 10 seconds of
Universal Time.
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