Bill Blevins Management of the West-North Stability Limit Under the Nodal Market.

Bill Blevins

Management of the West-North Stability Limit Under the Nodal Market

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Issue

• During the first two months following the transition to the Nodal Market, there have been some days in which ERCOT has had challenges managing the West-North Stability Limit

• Four days are specifically looked at in the following slides (12/15, 12/20, 12/27, and 1/20)

• What appears to have contributed to this:– Resources simply generating above their SCED base point, both

curtailed and un-curtailed (wind ramping periods)– Ineffective market/reliability incentives to follow base points (i.e.

LMPs, no base-point deviation charge, minimum GREDP intervals)– HSLs representing the

• QSEs sending inaccurate HSLs (i.e. setting HSL and output equal, even during curtailment) which could cause the constraint to become binding or release at the inappropriate time

• HSLs, even when accurate, are delayed so that QSEs can detect curtailment instructions

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The W-N Stability Limit

The W-N Stability Limit monitors 6 lines indicated by the circles

There are over 60 individual WGRs with a 70% or greater shift factor on these 6 lines

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Management on December 15th

• On the 15th, the W-N limit of 1691 resulting in the system being able to accommodate ~4000 MW of West Texas WGR output

• During the period in which the W-N limit was being violated, WGRs in the West, in aggregate, generated over their base-point by as much as 600 MW

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Management on December 15th

• During this time, the Resource LMPs for the West WGRs went to approximately $1 and did not go below -$3

• ERCOT Operators have been controlling to 92% of the W-N Limit and this adjusted down gradually to 80% between 11:00 and 12:00

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Management on December 15th

• During this period on the 15th the high limits being telemetered to ERCOT decreased at the same time in which the resource outputs changed, however this trend was not observed in the average wind speed

• This indicates that the HSLs may have been set equal to output for some WGRs, even during periods of curtailment

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Management on December 15th

160MW Unit Trip

• At 11:31AM, breakers were opened to drop 160 MW of generation

• Last resources released to full output at 1:27PM

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Management Issues on December 20th

• Again on the 20th, the W-N limit of 1691 resulting in the system being able to accommodate ~4000 MW of West Texas WGR output

• During the period in which the W-N limit was being violated, WGRs in the West, in aggregate, over generated by as much as 345 MW

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Management Issues on December 20th

• The graph below shows more directly the impact on the of west WGRs not being on their base point on the W-N interface flow

• On the aggregate, the largest positive error that was observed as a percent was ~8%

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Management Issues on December 20th

• During this time, the Resource LMPs for the West WGRs went to between approximately -$5 and $0 and went as low as about -$23

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Management Issues on December 20th

• To a much smaller degree than on the 15th, the high limits being telemetered to ERCOT decreased at the same time in which the resource outputs changed even though this trend was not observed in the average wind speed

• There appears to have been some improvement in the QSEs abilities to send this information to ERCOT

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Management Issues on December 20th

• 11:09AM, W-to-N went over 100% and then back under

• At 11:45AM, W-to-N went over 100% again and hot-line call was made to QSEs representing WGRs to follow base-points

• There were no unit trips and GREDP performance improved after hot-line call was made

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Management on December 26th-27th

• On the 27th, the W-N limit of 1691 resulting in the system being able to accommodate ~4500 MW of West Texas WGR output

• During the period in which the W-N limit was being violated, WGRs in the West, in aggregate, generated over their base-point by as much as 370 MW

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Management on December 26th-27th

• The graph below shows more directly the impact on the of west WGRs not being on their base point on the W-N interface flow

• On the aggregate, the largest positive error that was observed as a percent was just under 10%

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Management on December 26th-27th

• During this time, the Resource LMPs for the West WGRs went to approximately -$20 and did not go below -$30

• ERCOT Operators have been controlling to ~85% of the W-N Limit and this adjusted down gradually to 78% after 0:30

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Management on December 26th-27th

• As on the 15th the high limits being telemetered to ERCOT decreased at the same time in which the resource outputs changed, however this trend was not observed in the average wind speed

• This indicates that the HSLs may have been set equal to output for some WGRs, even during periods of curtailment

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Management on January 20th

• On the 20th, the W-N limit of 1691 resulting in the system being able to accommodate ~4000 MW of West Texas WGR output

• During the period in which the W-N limit was being violated, WGRs in the West, in aggregate, generated over their base-point by as much as 430 MW

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Management on January 20th

• During this time, the Resource LMPs for the West WGRs went to approximately -$5 and then to -$20

• ERCOT Operators have been controlling to 87% of the W-N Limit and this adjusted down gradually to 85% after 3:00

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Management on January 20th

• On the 20th, the telemetered HSLs for WGRs tracked very well with the average wind speed even though the wind power output stayed relatively flat

• This indicates that there has been some improvement in the calculation of these values

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Impact of WGR Over-Generation on the SCED Solution

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Analysis of SCED curtailment flag and Resources not following SCED during W_N limit curtailments

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ERCOT Directives

• The hotline call was being issued to direct WGRs to not exceed the SCED dispatch– After SCED receives the constraint from the reliability system, a

Secure-Economic dispatch is developed which considers Resource economic curves and operating conditions

• The unscheduled flow of WGRs ramping higher than the SCED dispatch contributes to flows and creates an exceedance of the limit– The is true for all Resources, whether the Resource is being

“curtailed” or not• In order to more precisely dispatch the WGRs during this

period the directive was to be at or below the SCED dispatch since SCED base-points issued would not exceed the active limit

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New Procedure for ERCOT Operators

• The following process will be applied for future management of the W-N Stability Limit– Modified based on feedback from WGRs– Should reduce the need for directives to WGRs– ERCOT will adjust the limits used by forward-looking markets to be aligned with Real-Time

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New Procedure for ERCOT Operators

• What to expect from the Verbal Dispatch Instructions (VDIs)– Identification of the responsible Entity and instructing authority (to include ERCOT

Operator’s and receiving operator’s names);

– Specific Resources or TSP facilities that are the subject of the Dispatch Instruction;

– Specific action required;

– Current operating level or state of the Resources or TSP facilities that are the subject of the Dispatch Instruction;

– Operating level or state to which such Resources or facilities will be dispatched;

– Time of notification of the Dispatch Instruction;

– Time at which the QSE or TSP is required to initiate the Dispatch Instruction;

– Time within which the QSE or TSP is required to complete the Dispatch Instruction;

– VDI reference number; and

– Other information relevant to that Dispatch Instruction

• If the VDIs are severely impacting SCED dispatch (i.e. RLC-SCED is seeing the unit as available), the Resource’s HDL may be temporarily overridden

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Conclusions

• The contribution of “uncurtailed” WGRs to the West-North flow has created some challenges for ERCOT in controlling the limit

• Continued Nodal experience should improve control of the West-North Stability Limit– ERCOT Operators will gain a better understanding of what point reliability

actions need to commence to ensure/maintain reliability– QSE/WGRs should improve in their ability to telemeter accurate resource

limits and to detect curtailment instructions from ERCOT• A large amount of improvement has already been observed

• The implementation of NPRR 285 grey-boxed language should also help– A flag being sent to QSEs should make curtailment instructions even more

apparent– Potential base point deviation charges should add to the market incentives to

follow ERCOT instructions• The Protocols should continue to be reviewed to ensure the appropriate

rules are in place manage congestion efficiently and reliably