Summary

The transfer interaction analysis group of functions within PSS™MUST were developed for evaluating the impact of parallel transfers on the study transfer FCITC limits. These functions provide the answer to the commonly asked question, How do surrounding system transfers affect transfer limits?

PSS™MUST has a large variety of functions for transfer sensitivity analysis and reports, but the starting point for all types of analyses is the analysis of the impact on the specified study transfer FCITC for a change in a single parallel transfer.

Before performing a transfer sensitivity study, the user must specify a study transfer and compute the study transfer FCITC determined by the most restrictive constraint. When a change in the parallel transfer changes the flow on the most restrictive monitored element (branch or interface), the study transfer FCITC limits will also change. If a parallel transfer decreases the flow on the limiting element, the FCITC limits will increase. If a parallel transfer increases the flow on the limiting element, then FCITC limits will decrease.

It is possible to use study and parallel transfer network sensitivities (OTDF factors) to derive the Parallel Transfer Response Factor (PTRF). This factor is the ratio of change in study transfer FCITC to the change in parallel transfer. The PTRF can be computed by using the study and parallel transfer network sensitivities (OTDF factors).

As a result of using a linearized load flow model, all transfer sensitivity reports describe a piece-wise linear concave function. It is a concave function because every new more restrictive segment has a smaller or increasingly negative PTRF value.

Transfer sensitivity analysis provides answers to the following questions:

1. What constraints can be the most limiting at the different parallel transfer levels?



2. At what parallel transfer level does a new constraint become the most restrictive?



3. What are the PTRF values for the most restrictive constraint?

In most cases, there are not more than two or three most restrictive constraints within a relatively large range of change in parallel transfer. If there is only one limiting constraint, a user can use the linear extrapolation to identify FCITC at different parallel transfers levels using the PTRF value.

The transfer sensitivity analysis also provides reports on flows and PTDF, LODF, and OTDF factors for the most restrictive constraints.

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Parallel Transfer Detail Report

There are three basic types of reports providing different levels of detail:

1. MS Excel chart
2. Summary text report
3. Detailed text report

All these reports show how the study transfer FCITC changes with parallel transfer changes. At every parallel transfer level, a study transfer FCITC is determined by the most restrictive contingency/monitored element pair for the selected study transfer. Thus, to create a transfer sensitivity report with respect to the second limiting constraint, the user must exclude the first most limiting constraint using function EXCLUDE.

Under some conditions, the FCITC report might contain negative FCITC values. PSS™MUST will not generate summary and detailed reports for this condition. On MS Excel charts, PSS™aMUST stops plotting if FCITC reaches zero.

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Multiple Study Transfer Report

Multiple study transfer sensitivity reports provide a convenient way to identify how one additional transaction can impact a whole group of study transfers. These reports are useful for operational applications (OASIS posting) where a transmission provider wants to adjust the posted interface limits based on an additional transmission service reservation or schedule.

There are two basic types of reports providing different levels of detail:

1. MS Excel chart
2. Summary text report

An analysis chart shows that at the parallel transfer level 1820 MW, FCITC for all study transfers decrease to zero simultaneously. This happens only if the parallel transfer causes an overload by itself independent of the study transfer levels.

A summary table provides a simple and convenient solution for updating FCITC values in the operation environment. This type of table can be created for every single parallel transfer of interest and should be recomputed when schedule changes if there are study transfers with multisegment FCITC curves.

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Multiple Parallel Transfer Report

The multiple parallel transfer sensitivity report displays the impact of a selected set of parallel transfers on one study transfer FCITC.

There are two basic types of reports providing different levels of detail:

1. MS Excel chart
2. Summary text report

In general, the simultaneous impact of two or more parallel transfers on the study transfer FCITC cannot be obtained directly. The constraining contingency/limiting element pairs may be for different parallel transfers. In that case, the impacts of individual parallel transfers on FCITC limits cannot be added to obtain the total simultaneous impact on the study transfer. However, such superposition is possible to the left of the first inflection points of all the curves shown. For this range of parallel transfers, the constraining contingency/monitored element pair is the same pair that determines the nominal study transfer FCITC when all parallel transfers are zero.

Multiple parallel transfer reports on selected study transfers can be very useful to identify potential parallel transactions that may have a significant impact on the selected study transfer.

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October 12, 2006 03:37 PM			©2010 Siemens Energy, Inc., Siemens Power Technologies International (Siemens PTI) Schenectady, NY, USA			E D SE PTI