Columbia Grid Wind Integration Study Team Dynamic Transfer Capability Studies Update 9/10/09

Review Using North of Hanford as test case Dynamic Transfer Real-Time concerns: RAS Arming Voltage Control Methodology that can be automated and used consistently across all paths

DTC Study Assumptions The design assumptions for this initial roll-out of limits is to see how much transmission capacity can be allowed to operate dynamically with as much as full range changes every 4 sec without adding to the current dispatcher workload (e.g. RAS, voltage control, reactive reserves, curtailment due to nomogram interactions). Refinements to these assumptions may be done after the initial limits are created.

DTC Limit Criteria Given these assumptions, the design criteria for each limiting element are: RAS arming: dynamic transfer range limited to below what would require changes in RAS arming Voltage sensitivity: dynamic transfer range limited to what would create a 5kV change in bus voltage when no manual voltage control actions are taken (taps, shunt devices locked; AVR active). If the sensitivity less than 5kV / 100 MW transfer, the transfer amount will be zero (this level of change is an strong indicator of potential voltage instability). Reactive Reserve: dynamic transfer range limited such that significant changes in unit commitment is not required to achieve dynamic reactive reserve minimum levels. Effect on associated nomograms: dynamic transfer range limited so that use of the full range does not result in limitations to associated paths or potential SOL violations in real time due to rapidly moving SOLs. (An example of this is the interaction between Midpoint-Summer Lake flow and the COI SOL.) Effect of dynamic range on voltage and transient stability limitations: dynamic transfer range limited so that post-contingency simulations remain voltage and transiently stable.

North of Hanford Operation High NOH N-S flow occurs in summer. High NOH S-N flow occurs in late fall and winter. NOH N-S limits are needed to provide voltage stability for the loss of two units at Palo Verde. NOH N-S and S-N limit also needed to prevent thermal overloads in the area north of Hanford for the 500-kV double line loss of Schultz-Wautoma No. 1 and Vantage-Schultz No. 1. NOH DLL and NOH SLL Gen Drop are needed to prevent thermal overloads on the 115-kV and 230-kV transmission system in the Columbia and Vantage areas and voltage instability on the 500-kV grid in the area north of Hanford. NOH N-S flow above 3800 will reduce NJD limits to 7650 (step change) due to voltage stability concerns. North of Hanford also has minimum levels of reactive reserves to maintain based on the N-S flow across the path

RAS

Impact of RAS on DTC RAS arming for DLL and SLL occurs at flows exceeding 2800 N-S. RAS is fully armed at 4100 MW. There is no RAS for S-N flow. RAS workload resulting from NOH is likely to be limited to the summer operating period. Chasing transfers as they move within the arming range would be a significant effort (over much of this range, a 100 MW change in flow requires significant changes in the RAS arming

Voltage Stability Concerns What is the voltage sensitivity to dynamic transfers? How much transfer change is required before dV/dP limit (5kV / 100 MW) is reached (reliability issue)? How much change in flow is necessary to go from the high alarm to the low alarm (this triggers dispatch action)? What effect does operating at the extremes of the voltage alarms have on the study results (reliability)? The first two questions require tracking dV/dP and bus kV across multiple cases when the transfers are changed while keeping voltage control devices locked. The 3rd question requires taking one of the limit cases from questions 1&2 and running a contingency analysis on it.

Methodology The voltage sensitivity function calculates the dV/dP at a bus based on a 1 MW change at the Buyer and Seller. The dV/dP is reported as Vpu / 1 MW. For most points we consider, the slope of the voltage is not great (e.g. does not change much with flow), therefore it is reasonable to convert – and easier to understand – to kV / 100 MW. This is done by multiplying the dV/dP * 500 * 100.

Methodology dV dP

Methodology This gives us an easy way to calculate the sensitivity to voltage at the transfer levels given by each scenario. The sensitivity can then be used to multiply out the transfer allowed by using a multiplier based on a 5kV change. x MW = (5kV)( ) PTDF VkV

NOH Limit Case

Sample Results Ramping in the transfers themselves provide less conservative numbers, but are consistent. Difference is probably due to freeing up reactive by unloading generation and transmission.

Comparison of Source/Sink Pair

Next Steps Evaluating automation options Identify and build NI and NOH scenarios Calculate trial DTC “nomograms”