Composite Load Model Implementation Update Craig Quist/Rikin Shah, PacifiCorp May 15-17, 2013 TSS Meeting

Composite Load Model – Status Update… Following the last TSS meeting (January 2013) a request was submitted to members to reevaluate the composite load model using an updated load model representation. Responses from 11 (additional) entities were received by 4/11/2013 (due 3/29/2013) Responses received fit into 12 performance categories and two software/ data reevaluation categories, as noted in the table below: Composite Load Model - status update meeting w/M&VWG held on 3/26-28/2013 A summary of responses received is noted on the following pages:

Composite Load Model – Status Update… Arizona Public Service (APS): Analysis was performed on six different transmission paths (50, 22, 23, 51, PV East, 49) After five seconds, the frequency traces were noticeably different. From the results seen in this phase I assessment, the composite model’s performance is equal to or slightly better than the performance of the interim load model. At this time, we would recommend using the phase I model as opposed to the interim model.

Composite Load Model – Status Update… California Independent System Operator (CAISO): Loss of load is observed during 3-phase faults Post-transient voltage recovers to higher voltage Generators may go out-of-step Some small generators may go out of step because of under excitation SPS Modeling Considerations For contingencies that have SPS involving load tripping, switch files should be changed considering that the loads are moved to low voltages and distribution feeders are added. Reliability Criteria Violations An example may be Malin-Round Mountain 500 kV single line outage. With the composite load model, there were frequency criteria violations on several buses in Northwest.

Composite Load Model – Status Update… Chelan County Public Utilities District (CHPD): For the majority of the faults simulated, there was no significant difference between the two models. (This may be due to the dynamics of the generation having a much greater influence on our system than load.) While not one of the requested performance attributes, system angle was another factor that notably changed. While, several contingencies known for causing voltage issues were specifically chosen and run; in two of the instances the composite load model recovered to a higher voltage; while in a third instance, the composite load model failed to converge.

Composite Load Model – Status Update… El Paso Electric (EPE): Alamogpg 69 kV bus voltage The Arroyo 115 kV bus is taken as the benchmark bus representative of what would occur at all key EPE buses during an EPE Westmesa‐Arroyo 345 kV line (“EP line”) contingency. There were no voltage or frequency violations for the Arroyo 115 kV bus. However, there were some voltage violations and other unknown frequency excursions and unusual voltage recovery for the (TSGT) Alamogpg 69 kV bus. Results have been forwarded to Tri-State G&T.

Composite Load Model – Status Update… Nevada Energy (NVE): NV Energy used all three dyds for comparison, the 12hs4 composite load dyd, a 20% motorw dyd and a 50% motor w dyd. The voltage recovery in the 50% motorw dyd was similar to the voltage recovery using the composite load dyd. However, underfrequency load shedding was not correct per the incompatibility of the motorw models and the lsdt9 relays. NV Energy likes the performance of the composite load models and believes that their inclusion will be a needed improvement to transient stability studies. NV Energy is confident that the performance will be correct and that the only issues at this time for Area 18 and Area 64 are incomplete channel reporting. NV Energy would like some assistance in developing a winter peaking commercial/industrial residential load that represents a ski area load. *ASSISTANCE REQUEST*

Composite Load Model – Status Update… NorthWestern Energy (NWE): PSS/E composite load models not available Black Hills Corporation

Composite Load Model – Status Update… Portland General Electric (PGE): Post transient voltage recovery at PGE load buses was observed to recover at a higher voltage for some studied outages and at a lower voltage than the interim model for others, and Delayed frequency recovery was also observed at various buses for some outages. Typically the composite load model has a more exaggerated response than results seen using the interim model this is expected due to the higher power draw during the fault and initial motor tripping immediately after clearing. We believe there could be a potential Reliability Criteria violations using the new model so we would recommend that Phase I be recommended as is and that Reliability Sub-committee precede with its own evaluation of the performance requirements, and consider loosening the performance criteria for frequency recovery times.

Composite Load Model – Status Update… Sacramento Municipal Utility District (SMUD): Rancho Seco – Bellota double line outage results in an unexpected higher overall frequency in the WECC system which settled at 60.0214 Hz. This maybe the result of tripping off some of the motor load components on the composite load model The composite load model study results show lower voltage during fault (due to larger power draw), higher and faster initial recovery and higher post-transient voltages (1.02 pu - see attached plot).

Composite Load Model – Status Update… Salt River Project (SRP): Composite Load Modeling evaluated Path 54 at its rated value. SRP found significant issues and does not recommend implementation of “Phase I” Composite Load Model while the issue of WECC Criteria from TPL-001-WECC-RBP-2 is not resolved.

Composite Load Model – Status Update… PacifiCorp (PAC): Additional analysis was performed to compare the composite load model implementation in the PTI PSS/E vs. GE PSLF software packages. Utilizing a three bus test case, analysis focused on two scenarios: No fault @60 cycles, no fault – open line 101-102 #1 and line 101-103 #1 @20 seconds, terminate the simulation Three-phase faulted lines @60 cycles, 3-phase fault on GEN115 bus 101 @65 cycles, clear the fault with loss of line 101-102 #1 and line 101-103 #1

PacifiCorp – PSS/E vs PSLF (Scenario: No Disturbance)

PacifiCorp – PSS/E vs PSLF (Scenario: No Disturbance)

PacifiCorp – PSS/E vs PSLF (Scenario: Three-Phase Fault)

PacifiCorp – PSS/E vs PSLF (Scenario: Three-Phase Fault)

Shifting Gears… Transition from: Composite Load Model discussion to: PSLF-PSS/E Software Implementation Issue Discussion

PSLF – PSSE Conversion Status Update Bill Hall currently working on Conversion to PSSE V33 Lot of issues with wind turbine models. Issues with GE wind turbine models as well as the generic wind WT3 models. Currently working on resolving these issues. Able to initialize after gnetting all the wind generation. Functionality differences also causing the solution to change in the two different platforms. Hopefully will have the conversion completed in a month.

Recommendations PTI Users need to evaluate the Composite Load Model (CLM) Use PSSE Ver 32 “12HS” case available on WECC website. Limit the CLM to only a few buses in their system. Need to provide input on their evaluation. Present the results of the PTI evaluations to TSS. Recommend to RS the changes to the criteria for their evaluation. Entities believe that the criteria needs to be re-evaluated and changed before the CLM can be implemented in the WECC base cases. Changes to the TPL standards might be necessary Update the RC on the implementation. Finally implement the CLM throughout the system.