Electric Utility Solutions: Distributed Generation
Content
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) – 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
Distributed Generation Alternatives
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
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.
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.
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 drop or – By causing reverse power flow and reverse voltage drop
• The smaller your conductor, the greater your voltage rise.
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
Voltage Drop / Load Flow Demo
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
Typical Reactances for 40 to 2000 kW Generators
Name
Sub-transient reactance Transient reactance Synchronous reactance Zero seq. reactance Negative seq. reactance
Symbol xd’’ xd’ xd xo x2
Range in Per Unit .09 - .17 .13 - .20 1.7 – 3.3 .06 - .09 .10 - .22
Effective Time 0 to 6 cycles 6 cycles to 5 sec After 5 seconds
Cummins Power Generation, white paper, “Calculating Generator Reactances”
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.
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.
Fault Current Demo
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.
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.
Dan Harms
La Plata Electric Association 970-382-3514 [email protected]
Dan Harms La Plata Electric Association
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
Distributed Generation Alternatives
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
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.
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.
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 drop or – By causing reverse power flow and reverse voltage drop
• The smaller your conductor, the greater your voltage rise.
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
Voltage Drop / Load Flow Demo
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
Typical Reactances for 40 to 2000 kW Generators
Name
Sub-transient reactance Transient reactance Synchronous reactance Zero seq. reactance Negative seq. reactance
Symbol xd’’ xd’ xd xo x2
Range in Per Unit .09 - .17 .13 - .20 1.7 – 3.3 .06 - .09 .10 - .22
Effective Time 0 to 6 cycles 6 cycles to 5 sec After 5 seconds
Cummins Power Generation, white paper, “Calculating Generator Reactances”
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.
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.
Fault Current Demo
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.
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.
Dan Harms
La Plata Electric Association 970-382-3514 [email protected]
