Example ATC Calculation Procedure (Rated System Path Method)

Transcription

1 Example T alculation Procedure (Rated System Path Method) Seasonal ase ase MV MV Max Rating power transfer from to has been proposed and this example will attempt to demonstrate how the maximum possible reliable transfer is determined. This illustration displays flows that would be obtained from a seasonal base case power flow model, and represent the branches of the Identified - Path. Red quantities are maximum allowable flows based on most limiting equipment.,, & represent areas or points in the system that contain generation and/or distributed load. Note for this example: Total Transfer apability (TT) for each segment is considered equal to the maximum flow rating. Existing Transmission ommitments (ET) for each segment is equal to the flow shown here resulting from the base case power flow simulation.

2 Power Transfer from to Simulated during Normal System onditions MV 78 TF IT This is the limiting element because it can accommodate the least total transfer. In other words, if the generator and load were increased to 158MW, this branch would have MV flowing, and the flows on all other branches would be less than maximum. This figure illustrates how branch flows in the transfer path would change for an arbitrary but realistic interchange of 40MW. The flows shown here are during N-0 or normal system conditions with all elements in service. linear analysis is then used to calculate the maximum possible transfer: 1. alculate the Transfer istribution Factor (TF) for each branch. TF represents what fraction of the total transfer appears on a given segment. 2. alculate the Incremental Transfer apability (IT) for each branch. IT represents the maximum total transfer each branch could accommodate over and above base flows. 3. The branch with the lowest IT will be the limiting element for this transfer. 4. alculate the T for that limiting element: T = TT ET** 5. The T of this limiting element is considered the T for this - path during normal system conditions. Segment - is the limiting element in transfer path - with an IT = 158MV, therefore the T for path - is TT ET for this element. T = 28 = 87MV during N-0 onditions. Notice that simply calculating TT- ET for each branch and using the minimum would not yield the same results. **(TRM and M neglected and considered zero in this example)

3 Power Transfer from to Simulated during N-1 onditions (Loss of a Single Transmission Element) Standards state that T values shall be valid during normal system conditions (N-0) and single contingency conditions (N-1). Therefore, all significant outages within the system must be considered, and the previous analysis effectively repeated to determine the limiting path element during outage conditions. The following figures will attempt to demonstrate this analysis process. lthough only the five branch segments in this example are opened and the power transfer analyzed, the real power system must consider many more outages greatly exceeding those in the transfer path. FF 132 This is how much the flow changed This was the flow on the outaged branch FTF FIT MV MV Line Segment Out of Service The flows shown here are during N-1 or single outage conditions. The same linear analysis is performed to calculate the maximum possible transfer for this outage: 1. Introduce and calculate yet another quantity called First ontingency istribution Factor (FF) for each branch. FF represents what fraction of the flow that was on the outaged branch shifts and flows on the given branch. This value will be particularly useful when calculating Ts for slightly varying system conditions. 2. alculate the First ontingency Transfer istribution Factor (FTF) for each branch. FTF represents what fraction of the total transfer appears on a given segment. 3. alculate the First ontingency Incremental Transfer apability (FIT) for each branch. FIT represents the maximum total transfer each branch could accommodate, over and above base flows. 4. The branch with the lowest FIT will be the limiting element for this transfer and this outage. ranch - is the limiting element for this outage with an IT of 28MW. This means that during this outage, with these system conditions, only 28MW of total transfer would be possible. (neglecting TRM and M)

4 MV MV Line Segment Out of Service Line Segment Out of Service

5 MV MV Line Segment - Out of Service MV MV Line Segment - Out of Service

6 Interpreting the Results N-0 NLYSIS Segment - was the limiting branch in the Transfer Path because the Incremental Transfer apability was the smallest at IT=158. Therefore, the T for this - path during normal system conditions is: T for Path = TT for this branch - ET for this branch (pre-transfer) T = 28 = 87MV N-1 NLYSIS Looking at the results of all outages, indicates that branch - is the limiting element for an outage of -. - had the smallest IT of 28, meaning that only 28MV of total transfer is possible if branch - is out of service. Therefore, the T for this - path during single outage conditions is: T for Path = TT for this branch - ET for this branch (pre-transfer, post-outage) T = 132 = 28MV The minimum of N-0, N-1 T determines the Overall T rating for this - path for these modeled system conditions. FINL RESULT.. Path - T = 28MV

7 alculating T for Varying System onditions fter the T analysis and istribution Factors are calculated, the T for this path can be determined for moderately varying system conditions. Using N-0 flows (possibly real time or historical S) on the worst outage element (-) and limiting element (-), a new T can be determined. onsider the known or predicted flows shown in the different normal system conditions figure below. What would be the resulting T for this - path? FF FTF 92 = 44+(1.0)* Forecasted Normal onditions Worst Outage onditions New Flow = Old Flow + FF*(pre-outage element flow) Using the Worst Outage results shows that - would have 92 MV of flow for worst outage conditions. With Total Transfer apacity of, these determine T = 92 = 68 MV. There is 68MV of apacity left on this line for further commercial activity. Since the FTF of this line is, means that 68/1.0 = 68MW of total transfer would be possible. If 68MW of total transfer is occurring, branch - would be loaded to MV while all other branches are less than maximum loaded. Other branch loadings could also be predicted using the istribution Factors calculated in the detailed T analysis. elow are the results which agree well with power flow model MW 34.8 MV MW Maximum Transfer uring Worst Outage Predicted onditions uthor: dan.lyons@aquila.com Use it any way you like