ATC Dialog Common Options: Transfer Result Reporting Options

 

These options are found in the Transfer Result Report Options section on the Common Options sub-tab of the Options page found on the Available Transfer Capability dialog.

 

Transfer Limiters To Save

This value tells Simulator how many total Transfer Limiters to save. Simulator will save those Transfer Limiters with the lowest Transfer Limitation. An explanation of a Transfer Limiter follows:

During Linear ATC Analysis, Simulator determines the Transfer Limitation (See Available Transfer Capability Analysis) for each transmission line and interface during each contingency and the base case. From this Simulator develops a list of Transfer Limiters. A Transfer Limit contains three key pieces of information:

Thus if we are monitoring 1000 transmission lines during 99 contingencies plus 1 base case, there would be 100,000 Transfer Limiters calculated. We are not concerned with all 100,000 limitations, therefore, only the limitations with the smallest Transfer Limit in MW are reported.

Max Limiters per CTG

When analyzing a long list of contingencies, the worst transfer limitations may all occur during the same contingency. Set this value to limit the number of Transfer Limiters saved that are associated with a given contingency.

Max Limiters per Element

When analyzing a long list of contingencies, the worst transfer limitations may all be overloads of the same limiting element. Set this value to limit the number of Transfer Limiters saved that are associated with a given Limiting Element.

Max MW Limitation

This value defines the maximum transfer to report between the buyer and seller. Simulator will compute the ATC analysis results until the transfer amount reaches the value in this field and only report the results meeting the other reporting criteria up to this MW limitation.

When using one of the iterated methods, this option is only applied during the initial Single Linear Step portion of the method. Once individual limiters are being iterated on, this option will be ignored.

Ignore Elements with OTDFs below

Simulator will only report Transfer Limitations for elements with OTDF values greater than this user-specified value. The default value is 0.5%, meaning that for a 100 MW transfer, there would be only a 0.5 MW increase in flow on the Limiting Element. The OTDF cutoff is only used with transfer limitations that include contingencies.

Ignore Elements with PTDFs below

Simulator will only report Transfer Limitations for elements with PTDF values greater than this user-specified value. The default value is 0.5%. The PTDF cutoff is only used with transfer limitations that do not include contingencies, i.e. base case limitations.

 

For interfaces that include contingent elements, no additional contingencies will be studied on top of the contingencies that are part of the interface. The cutoff value to use for the OTDF is the minimum of the OTDF and PTDF cutoff values.

 

The transfer limitation functions involve dividing by the PTDF or OTDF values for each branch or interface to calculate the Transfer Limit. This leads to two facts:

These two facts often result in Linear ATC analysis reporting inaccurate transfer limitations for lines that are largely unaffected by the transfer. It is not uncommon to have a transfer limitation report an extremely negative transfer limit (e.g. -1.9E28 MW). A branch which is overloaded by a very small percentage, but which has a very small OTDF value often causes this. If the OTDF value is 0.001%, then a branch overloaded by 1 MW will result in a transfer limitation of -100,000 MW.

This motivates the usefulness of ignoring elements with small PTDFs and OTDFs.

 

All of these options work together to determine the list of limiters that shows up in the results. The Limit Monitoring Settings determine elements that will be considered for monitoring. The list of defined contingencies determines the contingencies. Every combination of monitored elements and contingencies will be tested. Monitoring exceptions can also be used to include or exclude monitored elements on a contingency-by-contingency basis. If the PTDF and/or OTDF cutoffs, as appropriate, are met for the monitored element/contingency pair, the monitored element and contingency are then checked against the Max Limiters per Element and Max Limiters per CTG conditions.

For each monitored element, a maximum, X, of Max Limiters per Element is kept during the initial processing. Only the most limiting X limiters for that element are retained. The transfer limiter with the highest transfer limit value will get pushed out of the list for an element if a new combination of monitored element/contingency is more limiting than what is currently in the list. For each contingency, a maximum, Y, of Max Limiters per CTG is kept during the initial processing. Only the most limiting Y limiters that for contingency are retained. The transfer limiter with the highest transfer limit value will get pushed out of the list for a contingency if a new combination of monitored element/contingency is more limiting that what is currently in the list. Once all monitored element/contingency pairs have been processed, all of the individual lists for limiting elements and contingencies are merged into one big list that is sorted by transfer limit, limiting element, and contingency. This sorted list is then traversed in the order of increasing transfer limit to create the final list that enforces the Max Limiter per Element, Max Limiters per CTG, Transfer Limiters to Save, and Max MW Limitation conditions. If there are no monitored element/contingency pairs that are below the Max MW Limitation, the monitored element/contingency pair with the lowest transfer limit value will be the only record reported in the results.

The following is an example of how this process works:

Max Limiters per CTG = 2, Max Elements per Limiter = 1

 

Limiting Element Lists

Line A contains transfer limiter for CTG B with ATC = 500

Line B contains transfer limiter for CTG B with ATC = 50

Line C contains transfer limiter for CTG X with ATC = 125

Line D contains transfer limiter for CTG A with ATC = 750

Line H contains transfer limiter for CTG B with ATC = 10

Line Z contains transfer limiter for CTG D with ATC = 10

 

Contingency Lists

CTG A - Line B with ATC = 1500, Line C with ATC = 1750

CTG B - Line H with ATC = 10, Line Z with ATC = 25

CTG C - Line D with ATC = 1000

CTG D - Line Z with ATC = 10

CTG X - Line C with ATC = 125

 

Now combine the lists and sort based on ATC, limiting element, and contingency. Duplicate entries can exist in the list because the same limiting element/contingency pair can be stored in both the limiting element list and the contingency list.

10 Line H/CTG B

10 Line H/CTG B

10 Line Z/CTG D

10 Line Z/CTG D

25 Line Z/CTG B

50 Line B/CTG B

125 Line C/CTG X

125 Line C/CTG X

500 Line A/CTG B

750 Line C/CTG A

1000 Line D/CTG A

1500 Line B/CTG A

1750 Line C/CTG A

 

Now go through the sorted list above to produce the final results list that abides by all conditions.

10 Line H/CTG B

10 Line Z/CTG D

50 Line B/CTG B

125 Line C/CTG X

1000 Line D/CTG A

 

 

Include Contingencies Check Box

Check this box to include contingencies (inserted or loaded using the Contingency Analysis Tool) in the ATC analysis. Note that minimizing the number of contingencies considered greatly improves solution speed as well as computer memory requirements for doing ATC Analysis. Therefore, be careful in choosing which contingencies to use with the ATC tool. Setting the Skip field to YES for a particular contingency will exclude it from the ATC analysis.

The ATC tool uses the same contingency records as the contingency analysis tool. Contingency results may be invalid following ATC analysis. If necessary, save contingency results to an auxiliary file prior to running the ATC analysis.

Contingency elements have an associated Status that determines under what conditions a particular action will be implemented. When ATC values are calculated using linear methods, contingency actions are not actually implemented. Because contingency actions are not actually implemented, POSTCHECK and TOPOLOGYCHECK actions cannot be applied after other actions have been performed and the power flow has been solved. By default, POSTCHECK and TOPOLOGYCHECK actions act as CHECK actions during linear ATC analysis (Single Linear Step Method). During linear ATC analysis whether or not model criteria are met for CHECK, POSTCHECK, AND TOPOLOGYCHECK contingency actions will be determined at the base transfer level rather than at the transfer level that determines the limiting transfer. The base transfer level is the transfer level at which the linear ATC values are actually determined. In most cases this will be the zero transfer level, but this can be different if using one of the iterated ATC methods.

There Iterate on Action Status option that can be set with contingency options, will allow conditional actions to be treated more accurately as part of the linear step calculations. Instead of treating all TOPOLOGYCHECK and POSTCHECK as CHECK actions, these actions are processed after other actions have been linearly implemented. See the Contingency Iterated Linear Analysis topic for details on this process.

Report Base Case Limitations Check Box

When checked, the ATC tool will report transfer limitations from the base case (pre-contingency).

Report Generation Reserve Limitations Check Box

When checked, the ATC tool will report transfer limitations from generation reserve.

Generator and load MW limits are not enforced when calculating linear sensitivities used to determine the transfer MW limits. However, checking this option provides an indication of when power transfers are limited based on generator maximum or minimum MW limits or the amount of load that is on-line. When this option is checked and there are limitations to how much power can be transferred because of max/min generator limits or the on-line load, additional Transfer Limiters will be present in the results. The Limiting Element will indicate either the Buyer or Seller and the Transfer Limit in MW will be the amount of transfer that can be achieved before the Buyer or Seller exceeds some limitation to generation or load. When considering reserve limits for the Seller, generators will be included in the reserve limit by taking the difference between the generator maximum MW limit and the present output and loads will be included in the reserve limit by the present amount of on-line load. When considering reserve limits for the Buyer, generators will be included in the reserve limit by taking the difference between the present output of the generators and the minimum MW limit and loads will be included by an arbitrary value of 9999.9 MW. Loads are included in this manner because maximum and minimum limits on loads are not currently used in the ATC tool.

For example, assume than an area that currently has 200 MW on-line and a total maximum MW output of 250 MW for all on-line generators that are on AGC control is defined as the Seller. A 50 MW generation reserve limitation will be reported for this area. As another example, assume that an injection group currently has 50 MW of on-line generation with a total maximum MW output of 150 MW and 50 MW of on-line load is defined as the Seller. A 150 MW reserve limitation will be reported for this injection group.

No generation reserve limitations are reported when the seller or buyer type is a bus or the slack.

If using one of the iterated methods, this option will be ignored except during the first single linear step. Reserve limitations may be reported from this step, but limitations of this type will not be iterated on during the individual iteration process. If choosing to enforce generator MW limits appropriately with the type of transactors that are defined, reserve limits will still be reported, regardless of this option setting, if they are hit during any step of the iterative process when ramping is occurring. See the detailed descriptions of either the Iterated Linear Step (IL) or Iterated Linear Step (IL) then Full CTG Solution method for more information about how reserve limits are checked during the iterated methods.

Use Options for Heatmap from FERC Order 2023

FERC Order 2023 has a requirement for providing heatmap information to allow prospective interconnection customers to see available interconnection capacity. Part of this requirement is to calculate "incremental injection capacity... under N-1 conditions". The ATC tool can be used for the calculation of the incremental injection capacity, given as the Trans Lim value in the ATC results, with the appropriate setting of the Transfer Result Reporting Options within the tool. Checking this option will set the other options appropriately for this calculation.

Using this option assumes the following: Modified in version 23, build on Oct. 10, 2024

 

The ATC Min Trans Lim field with a bus can be used to define a contour representing the heatmap. This field shows the minimum Trans Lim value of the transfer limiters calculated for the transfer direction with the respective bus as the Source. Multiple Directions calculations must be used for this field to be populated. The Sink of the transfer direction does not matter, but only a single transfer direction for each bus can be defined.