Distributed Generation
Dan Harms
La Plata Electric Association
Audience Survey
• Who has…
– Single residential windmills
– Wind farms
– Single residential solar
electric (1 to 10 kW)
– ...
Distributed Generation Alternatives
Modeling Considerations
• WindMil’s “Generation Model” settings
– Negative Load
• Simply adds a given source of kW and kVA...
Negative Load

• Use on solar electric, small windmill, micro
hydro, and other inverter-based systems
• Use on induction g...
Swing kVAr
• Use on synchronous generators where VAr flow
can be adjusted through field excitation.
• Requires detailed kn...
Generation Model Demo
Generation Studies

•
•
•
•

Voltage Drop / Sag / Flicker
Load Flow
Fault Current
Coordination
Generation – Voltage Drop
• A generator will cause your voltage to rise
– Either by reducing current and therefore voltage...
Generation – Voltage Drop (cont.)
• What happens if the generator drops offline?
– If in-line with regulators, they will n...
Voltage Drop / Load Flow Demo
Generation – Fault Current
• Generator impedance options for fault
contributions
– Sub-transient (xd’’)
• Determines maxim...
Typical Reactances for 40 to 2000 kW Generators
Name

Symbol

Sub-transient reactance

xd’’

Range in Per
Unit
.09 - .17

...
Fault Current – Inverter Based Systems
• Inverter based systems
– PV, residential wind, micro hydro, and some bio-mass
– N...
Fault Current – Large Wind
• Wind Generation
– Reactive power is modulated.
– Capacitive current is injected to maintain v...
Fault Current Demo
When to Model Generators
• Is the generator relatively large to the tap /
feeder / substation it’s on?
– If system has cap...
Summary
• WindMil can model any generator, but you need
to know how best to model what you have.
– Generator type
• Synchr...
Dan Harms
La Plata Electric Association
970-382-3514
dharms@lpea.coop
Electric Utility Solutions: Distributed Generation
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Electric Utility Solutions: Distributed Generation

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One more systems engineering and analysis focused presentation from Milsoft's 2009 User Conference. It was originally presented by Dan Harms. The Milsoft Electric Utility Solutions Users Conference is the premier event for our users and the vendors who provide interoperable solutions or services that enhance Milsoft Smart Grid Solutions. If you’d like to be on our mailing list, email: missy.brooks@milsoft.com.

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Electric Utility Solutions: Distributed Generation

  1. 1. Distributed Generation Dan Harms La Plata Electric Association
  2. 2. Audience Survey • Who has… – Single residential windmills – Wind farms – Single residential solar electric (1 to 10 kW) – Commercial solar (10 to 500 kW) – Solar farms (over 500 kW) – Biomass – – – – – Micro hydro / hydro Waste heat recovery Natural gas turbines Diesel engines Algae biofuel
  3. 3. Distributed Generation Alternatives
  4. 4. Modeling Considerations • WindMil’s “Generation Model” settings – Negative Load • Simply adds a given source of kW and kVAr – Swing kVAr • Generator maintains a settable per unit voltage • kW output held constant • kVAr swings leading/lagging to hold voltage
  5. 5. Negative Load • Use on solar electric, small windmill, micro hydro, and other inverter-based systems • Use on induction generators • Use on some synchronous generators – Depends on mode of generation – If maximum power output is a priority, generator terminal voltage can be adjusted in lieu of VARs.
  6. 6. Swing kVAr • Use on synchronous generators where VAr flow can be adjusted through field excitation. • Requires detailed knowledge of generator’s capability – You will need control setting information. – It’s unlikely that 5 kW generator could bring voltage up to 1.2 PU. • Make sure your VAr output is not exceeded.
  7. 7. Generation Model Demo
  8. 8. Generation Studies • • • • Voltage Drop / Sag / Flicker Load Flow Fault Current Coordination
  9. 9. Generation – Voltage Drop • A generator will cause your voltage to rise – Either by reducing current and therefore voltage drop or – By causing reverse power flow and reverse voltage drop • The smaller your conductor, the greater your voltage rise.
  10. 10. Generation – Voltage Drop (cont.) • What happens if the generator drops offline? – If in-line with regulators, they will not be boosting as much – If OCR trips and recloses, generation is gone, load is still there, regulators have to catch up – Run voltage drop with generation in place, lock regulators, remove generators, run voltage drop again
  11. 11. Voltage Drop / Load Flow Demo
  12. 12. Generation – Fault Current • Generator impedance options for fault contributions – Sub-transient (xd’’) • Determines maximum instantaneous current • Select AIC rating for breaker. – Transient (xd’) • Determines current at short time delay of breakers – Steady-State (xd) • Determines steady state current without excitation
  13. 13. Typical Reactances for 40 to 2000 kW Generators Name Symbol Sub-transient reactance xd’’ Range in Per Unit .09 - .17 Transient reactance xd’ .13 - .20 6 cycles to 5 sec Synchronous reactance xd 1.7 – 3.3 After 5 seconds Zero seq. reactance xo .06 - .09 Negative seq. reactance x2 .10 - .22 Cummins Power Generation, white paper, “Calculating Generator Reactances” Effective Time 0 to 6 cycles
  14. 14. Fault Current – Inverter Based Systems • Inverter based systems – PV, residential wind, micro hydro, and some bio-mass – No rotating parts and no inertia – Fault contribution 1 to 1.2 times rated output • Go to the impedance calculator in the Equipment Editor for the generator. • Enter full load amps x 1.2. – Use this impedance model for steady state, subtransient, and transient.
  15. 15. Fault Current – Large Wind • Wind Generation – Reactive power is modulated. – Capacitive current is injected to maintain voltage. – Model as Swing kVAr or use negative load with capacitors. – Fault contribution depends on turbine type and control settings. – Work with turbine manufacturer to determine fault contribution capability.
  16. 16. Fault Current Demo
  17. 17. When to Model Generators • Is the generator relatively large to the tap / feeder / substation it’s on? – If system has capability of backfeeding about 5% of the load of the tap it’s on, model it. • My personal preference • Net metered? – If excess generation doesn’t reach grid, don’t model it. – WindMil doesn’t allocate to negative billing load.
  18. 18. Summary • WindMil can model any generator, but you need to know how best to model what you have. – Generator type • Synchronous, induction, inverter – Control settings • VAr control? – Fault characteristics • Rotating inertia? • Talk to manufacturer.
  19. 19. Dan Harms La Plata Electric Association 970-382-3514 dharms@lpea.coop

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