Solar Impact Case Study Trishia Swayne, P.E. Leidos
Introduction Clean Energy Outlook
Agenda Case study profile Load scenarios determined Base case model established Analysis and results Summary and mi@ga@ons
Case Study Profile 298 kw of proposed PV Two primary points of interconnec@on through exis@ng u@lity distribu@on transformers Four interconnec@on step down transformers within camp Two 23 kw inverters and nine 28 kw inverters total Primary distribu@on voltage of 13.2 kv; only one circuit served from the substa@on transformer Site is 3.4 miles from the substa@on There is 5,135 feet of secondary overhead construc@on within the camp to interconnect the inverters The circuit has 8.1 kw of exis@ng rooqop, residen@al solar
Case Study Profile PV Site Substa'on
Load Scenarios One year of hourly circuit data provided (MW, MVAR)- Filter to day@me hours only PEAK MIN
Base Case Model Regulator and capacitor verifica@on Pole # Phase Size Layout Hold Voltage Bandwidth Compensa'on (R) Compensa'on (X) Time Delay K45399 A 219 Pole 126 2 0 0 75 K44869 A 50 Pole 125 2 5 0 45 K44867 B 100 Pole 122 2 8 0 45 K44868 C 100 Pole 123 2 5 0 45 175145 A 219 Pla\orm 124 2 1 0 60 175145 B 219 Pla\orm 124 2 3 0 60 175145 C 219 Pla\orm 124 2 1 0 60 K45291 C 100 Pole 122 2 8 0 75 Pole # KVAR Total Type Control Phase Can Size(s) Voltage 165747 50 Fixed 50 4.16 K44892 150 Fixed 50 4.16 K45154 600 Time Controlled A 200 13.2 K45416 50 Fixed 50 2.4
Base Case Model Add exis@ng/queued PV to model Pole Interconnected? Type kw 129829 Yes as of 12/11/2012 PV 4.085 K45473 Yes as of 10/8/2014 PV 4
Analysis Reverse power flow problem iden@fica@on Voltage and capacity review Voltage flicker analysis Short circuit analysis Risk of islanding assessment
Analysis - Reverse Power Flow Load dura@on curve at substa@on transformer (day@me hours only) 0.063 MW
Analysis Voltage and Capacity Pre and post project load flows conducted Primary feeder voltage remains within planning criteria (126 V 118 V) Conductor capacity issues were not iden@fied High voltage was iden@fied on the secondary side of the project site, as high 146 V Bank of single- phase line regulators will experience reverse power flow
Analysis Voltage and Capacity
Analysis Voltage Flicker Analysis Criteria for this u@lity is IEEE 519; all PV in the model is studied in on/off format
Analysis Voltage Flicker Analysis Allowable Primary System Min Load Flicker (%) Max Load Flicker (%) Secondary System Min Load Flicker (%) Max Load Flicker (%) 2% 0.23% 1.03% 15.94% 16.46%
Analysis Short Circuit The primary transformers at the two points of interconnec@on are grounded wye on both windings The four new transformers within the camp are also grounded wye on both windings The inverters are able to @e to the neutral of the step- transformers, crea@ng a solidly grounded system
Analysis Short Circuit Effec@ve grounding calcula@ons indicate the system is effec@vely grounded with the project online, based on IEEE 142 0 < X0 < 3 X1 0 < < 1 R0 X1
Analysis Short Circuit Analysis was conducted to confirm if overvoltages on unfaulted phases at the point of interconnec@on would be of concern Use fault flow in WindMil to evaluate
Analysis Short Circuit Run fault current and determine if fault currents on the feeder exceed interrup@ng ra@ngs GEN Status Fault Loca'on LG LG LLL LLL Maximum % Fault (Amps) (MVA) (Amps) (MVA) Current Contribu'on OFF 13 kv Bus Substa@on 3,019 690 3,070 702 ON 13 kv Bus Substa@on 3,028 692 3,080 704 OFF 69 kv Bus Substa@on 4,346 5,193 4,982 5954 ON 69 kv Bus Substa@on 4,347 5,195 4,984 5957 0.33% 0.04%
Analysis Risk of Islanding Four- step analysis was conducted based on the November 2012 Sandia Suggested Guidelines for Assessment of DG Uninten@onal Islanding Risk report
Analysis Risk of Islanding Step 1: Determine whether the aggregate AC ra@ng of all DG exceeds 2/3 of the minimum feeder loading. If Yes, proceed to Step 2. If No, there is minimal risk of islanding and analysis is complete. Step 2: Determine whether QPV + Qload is within 1% of the total aggregate capacitor ra@ng within the island, or alterna@vely, use real and reac@ve power flow measurements or simula@ons at the point at which the island can form to determine whether the feeder power factor is ever higher than 0.99 (lag or lead) at that point for an extended period of @me. If Yes to either evalua@on, a detailed islanding analysis should be considered. If No, proceed to Step 3. Step 3: Determine whether the poten@al island contains both rota@ng and inverter- based DG, and the sum of the AC ra@ngs of the rota@ng DG is more than 25% of the total AC ra@ng of all DG in the poten@al island. If Yes, a detailed islanding analysis should be considered. If No, proceed to Step 4. Step 4: Sort the inverters by manufacturer, sum up the total AC ra@ng of each manufacturer s product within the poten@al island, and determine each manufacturer s percentage of the total DG. If no single manufacturer s product makes up at least 2/3 of the total DG in the poten@al island, then further study may be prudent. If the situa@on is such that more than 2/3 of the total DG is from a single manufacturer, then the risk of uninten@onal islanding can be considered negligible.
Analysis Risk of Islanding Y indicates risk Poten'al Island Step 1 (Y/N) Step 2 (Y/N) Step 3 (Y/N) Step 4 (Y/N) Circuit 3096 Y Y N N
Analysis Summary & Mi@ga@ons Viola'on Reverse power flow at substa@on Excessive voltage flicker at site secondary Excessive steady state voltage at inverters Reverse power flow at bank of line regulators Risk of uninten@onal islanding Mi'ga'on Replace substa@on regulator controls Construct primary construc@on to site instead of ~1 mile of secondary Replace regulator controls Direct Transfer Trip (DTT)
Ques@ons Trishia Swayne, P.E. Leidos Director Interconnec@on Studies Email: Trishia.S.Swayne@leidos.com Phone: 615-431- 3227