10 Market Manual Adjustment

Exceptional Dispatch

Broadly speaking there are two types of exceptional dispatch, namely commitments and energy dispatches. Although commitments can commit a unit on or off, generally most of the exceptional dispatch commitments are “on” commitments and “off” commitments are rare. Likewise regarding energy dispatches the dispatch can either be incremental or decremental. Incremental dispatches are the most common, and decremental dispatches are infrequent but not rare. Regarding the timing of these dispatches, the ISO can issue exceptional dispatch instructions for a resource as a pre day-ahead market unit commitment, a post day-ahead market unit commitment or a real-time energy dispatch. A pre day-ahead market unit commitment is an exceptional dispatch instruction committing a resource at or above its physical minimum (Pmin) operating level prior to any of the day-ahead market runs. A post-day-ahead market unit commitment is an exceptional dispatch instruction committing a resource at or above its Pmin operating level in the real-time market.

A real-time exceptional dispatch instructs a resource to operate at or above its physical minimum operating point. For the purposes of this report, a real-time exceptional energy dispatch above the resource’s day-ahead award is considered an incremental exceptional dispatch instruction and a real-time exceptional energy dispatch below the day-ahead award is considered a decremental dispatch instruction. The ISO issues exceptional dispatch instructions primarily to manage constraints that are not modeled in the market software. In addition to constraints, the ISO also issues exceptional dispatch instructions relating to reliability requirements and, on occasion for software limitations and software failures. Reliability requirements are calculated for both local area and the system wide needs, and are classified into various requirements including local generation, transmission management, non-modeled transmission outages, and transmission management due to fires, ramping requirements and intertie emergency assistance. Whenever the ISO issues an exceptional dispatch instruction, these instructions are logged by the operators into the scheduling and logging system (SLIC), including an associated reason for each exceptional dispatch instruction.

Figure 78 below shows exceptional dispatch volume by market type: day-ahead, and real-time. All post-day-ahead exceptional dispatches are classified as real-time because those exceptional dispatches are settled in the real-time market. The total volume is calculated as sum of physical minimum of the resource, uneconomical incremental exceptional dispatch or uneconomical decremental exceptional dispatch. The total volume of exceptional dispatch in February dropped to 27,072 MWh from 36,080 MWh in January.

Figure 78: Total Exceptional Dispatch Volume (MWh) by Market Type

Figure 79 below shows the exceptional dispatch volume by reason. The majority of the exceptional dispatch volumes in February was driven by planned transmission outage (49 percent) and voltage support (40 percent).

Figure 79: Total Exceptional Dispatch Volume (MWh) by Reason

Blocking of Commitment Instructions

Figure 80 shows the count of commitment instructions that were blocked in any of the four RTUC runs for the corresponding month; the instructions are grouped by startups and shutdowns.

Figure 80: Daily Count of Commitment Instructions Blocked in RTUC

Blocking of Real-Time Dispatch

Figure 81 shows the daily volume in MWh of dispatches blocked in the real-time five-minute dispatch. First, the difference between the previous dispatch and the current dispatch that is being blocked is estimated. These differences are then converted into MWh by mutiplying the differences by a factor of 1/12, and summing across all intervals of each day.

Figure 81: Daily Volume of Dispatches Blocked in RTD

Adjustments of Transmission Constraints

In operating the markets the ISO, under certain circumstances, will adjust operating limits for selected flowgates (also known as transmission interface) constraints that become binding consistently in the day-ahead and real-time markets. This is done to ensure that measurable or predictable differences between actual and market-calculated flows are accounted for and adequate operating margins are maintained such that reliability of the grid is not adversely impacted.

Adjusting transmission constraints to maintain adequate operating margins is a prudent operating practice that was also used by the ISO prior to the launch of the new markets. With the implementation of the new markets based on locational marginal pricing (LMP), the market optimization tools used in conjunction with the full network model (FNM) in the day-ahead and real-time markets now perform congestion management through automated processes that calculate locational energy prices that reflect the costs of congestion at such locations. The new markets have not, however, eliminated the occurrence of measurable and often predictable differences between actual and market-calculated flows. The process of adjustments is, therefore, a necessary operational tool for ensuring that the markets result in schedules and real-time dispatches that more accurately reflect expected real-time flows, respect actual flow limits and fully support reliable grid operation. Note that adjustments are not applied to scheduling limits; they are applied only to market operating limits for certain branch groups (flow gates/transmission interfaces), as necessary. The key reasons for adjusting operating limits in the day-ahead and real-time markets are:

A. To align calculated market flows with measurable or predictable actual flows;

B. To accommodate mismatch due to inherent design differences of day-ahead market, real-time unit commitment and the real-time dispatch runs;

C. To allow reliability margins for certain flowgates; and

D. To adjust margins for flowgates impacted by telemetry issues.

Figures 82, 83, and 84 shows the transmission adjustment for the given month. These plot show two different metrics.

1. The bars in blue show the frequency of limit adjustments that were applied to the various flow-gates in either the integrated forward market, real-time unit conmmitment or real-time dispatch. This frequency only counts the time in which limits were adjusted while they were being enforced in the markets. The reference time for this frequency is based on all time intervals in the month even if the the transmission constraint was not enforced all the time.
2. The lines on the graph shows the miniumum and maximum conformance utilized for individual constraint.

Figure 82: Frequency and Average of Adjustments to Transmission Constraints in IFM

Figure 83: Frequency and Average of Adjustments to Transmission Constraints in FMM

Figure 84: Frequency and Average of Adjustments to Transmission Constraints in RTD