1. Modeling DER in Transmission Planning CAISO Experience
Irina Green
Regional Transmission Senior Advisor, California ISO
WECC MVWG, March 2017

2. DER Types (NERC Reliability Guideline)
Utility-Scale Distributed Energy Resources (U-DER): directly connected to the distribution bus or through a dedicated, non-load serving feeder. They are three-phase and can range in capacity, for example, from 0.5 to 20 MW
Retail-Scale Distributed Energy Resources (R-DER): offset customer load. Include residential, commercial, and industrial customers. Typically, the residential units are single-phase while the commercial and industrial units can be single- or three-phase facilities.
Distributed Energy Resources may include:
Distributed Generation – in front or behind the meter
Energy Efficiency – load modifier embedded in load forecast
Demand Response – demand or supply side, can be used as mitigation
Energy Storage – can be modeled as aggregated, supply or demand side

3. CAISO Modeling of Utility Scale and Retail Scale Distributed Generation (DG)
Supply-side DG - Utility Scale
Resources connected in front of the customer meter
Source: PTO Wholesale Distribution Access Tariff (WDAT) and CPUC RPS portfolio
Modeled at T/D interface as individual resource
Demand-side DG - Retail Scale (Behind-the-meter Generation)
Photovoltaic / Non-photovoltaic
Source: Embedded in CEC demand forecast
Modeled at T/D interface as aggregated resource (PV only at this time)
Behind the Meter solar PV modeled as a part of load

4. Output Level of DG
Select Behind the Meter-PV output using end-use load and PV profiles for the season and time of day of the studies.
40% DG output at the peak hour
DG output impacts which cases are the most critical and need to be studied

5. Data Source, MW of Behind-The-Meter PV Installed Capacity from CEC Forecast
Used locations of existing BTM-PV for existing installed PV capacity and used PTO Distribution Resource Plans geospatial maps to locate incremental Behind the Meter PV.

6. WECC Composite Load Model With DG
Substation transformer is included in the Composite Load Model. Utility-Scale DG modeled separately

7. Modeling Behind the Meter DG in Power Flow (GE PSLF)
Model calculated amounts of BTM-PV at each bus by specifying the P and Q values of the PV as separate entries in the power flow load data, including the following values:
Pdg - MW output of distributed generation
Qdg - MVAr of distributed generation (sign convention same as generators)
Stdg - DG status (1 – on-line)

8. Modeling Behind the Meter DG in Dynamic Stability (GE PSLF)
Model cmpldwg composite load model with distributed generation
DG type – solar PV
Initial Pdg method : 0) fraction of P load, 1) in MW, 2) Use P& Q from load table
Power factor
Current limit, per unit Imax
At which voltages and frequencies starts tripping and at which all DG is tripped
Fraction of DG that recovers when voltage or frequency recovers

9. DG Portion of Composite Load Model

10. Example, 3-phase, 4-cycle fault on the Midway-Vincent # 1 500 kV line
2026 Spring Off-Peak
Example, 3-phase, 4-cycle fault on the Midway-Vincent # kV line
Prior to Contingency: in WECC
Composite load: 66,027 MW
Composite load w/ DG: 9,000 MW
Behind the meter DG: 4,121 MW
After Contingency:
Composite load: 65,990 MW
Composite load w/ DG: 9,158 MW
Behind the meter DG: 3,768 MW
Lost: 353 MW DG, 390 MW of load
Stalling of Single Phase A/C disabled

11. Dynamic Simulation Results – Bus with DG
Initial:
Load 36.4 MW
DG 19 MW
Net load 17.4 MW
After contingency:
Load 34.1 MW
DG 9.5 MW
Net load 24.6 MW
Net load increased by 7.2 MW
DG tripped for low voltage: start tripping at 0.7 p.u, all tripped at 0.5 p.u, min voltage 0.53 p.u.

12. Dynamic Simulation Results: Composite Load Components, Bus with DG
Static load: initial 20.6 MW, final 20.2 MW, loss 0.4 MW
Electronic load: initial 6.1 MW, final 5.0 MW, loss 1.1 MW
Motor A: initial 2.8 MW, final 2.4 MW, loss 0.4 MW
Motor B: initial 2.2 MW, final 2.2 MW, loss 0.0 MW
Motor C: initial 2.1 MW, final 1.8 MW, loss 0.3 MW
Motor D: initial 2.6 MW, final 2.5 MW, loss 0.1 MW
Total loss of load 2.3 MW
Loss of DG 9.5 MW
Net load increased by 7.2 MW
Same Bus with DG

13. Same Bus, but DG Netted with Load
The result is different! Loss of load is higher if DG are not modeled explicitly

14. Composite Load Model with Single Phase A/C Stalling (Phase 2 of Composite Load Model)
No difference for the same contingency because the A/C didn’t stall
Different contingency:
Three-phase fault near large load: Potrero-Mission 115 kV
Voltage on the Potrero 115 kV bus, with DG not netted, voltage is lower

15. Load on Potrero Bus, two loads shown
Load # MW, and 6.8 MW DG (net 39 MW)
Load # MW and 1.2 MW DG (net 30.1 MW)
Load higher with DG modeled, because DG were tripped
Thus, voltage with DG modeled is lower

16. Same Contingency, DG Modeled on 115 kV Bus with PVD1 Model (Solar DG)
Three loads and three DG modeled with PVD1 models
Voltage at the Potrero 115 kV bus and at the feeder end
Same results with higher trip settings on DG
Load and generation, DG (PVD1) were not tripped
DG trip settings same as for composite load model (0.5 – 0.7 pu.)

17. 2026 Heavy Summer. 3 phase fault Mission-Potrero 115 kV
2026 Heavy Summer. 3 phase fault Mission-Potrero 115 kV. 3 Cases of DG, net load is the same
VOLTAGE ON MISSION 115 KV BUS
NET LOAD ON MISSION 115 KV BUS

18. Conclusions
Composite load model with behind the meter distributed generation is adequate
The model can be used in GE PSLF program and provides realistic results
For now, only distributed PV may be modeled with this model, more work may be needed to include other types of distributed generation
The study results are different when DG are modeled in the composite load model as generation and not netted with load.
The study results are different when DG are modeled as part of composite load model and when they are modeled as PVD1
Accurate models of Distributed Generation are important because it substantially impacts study results, especially the trip settings on load and on DG

19. Please send your comments to Irina Green
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