Transcript HECO Dynamics Seminar - Alaska Energy Authority Inc

NREL Wind Integration
Workshop
By Electric Power Systems, Inc.
June 28-29, 2010
Wind Integration in the Railbelt
•
Power Flow Results
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-
Few power flow issues introduced by wind
Few turbines have voltage regulation
Turbines with constant PF require close
coordination and study to optimize PF
setting for voltage control
Some turbines with PF control can be
changed in operation, others cannot
Slide 2
Wind Integration in the Railbelt
•
Energy Issues
-
-
-
Kenai wind energy exported to Anc/Fbks
reduces Bradley energy availability
Regulation on Kenai for wind energy in
Anc/Fbks reduces Bradley energy availability
due to transmission reservations for
regulation
Transmission regulation may warrant
uneconomic dispatch and unit commitments
for regulation
Slide 3
Wind Integration in the Railbelt
•
Short Circuit Results
-
-
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With no unit de-commitments, no SC
decrease issues
Inverter based systems limited by SC
availability in certain areas
Protection requirements impacted due to
limited SC current from WTGs
No uniform SC model for ASPEN, PSS/E or
other programs available
Slide 4
Wind Integration in the Railbelt
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Short Circuit Results
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SC coordination requires multiple fault
simulations for accurate scenario based on
fault location/duration
Fault current very close to WTG results in 5
X unit SC current (varies with WTG)
Fault current drops to almost unity within 5
cycles (varies with WTG)
Faults external to WTG plant result in 1.2 X
fault current (varies with WTG)
Slide 5
Wind Integration in the Railbelt
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Short Circuit Results
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-
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In some WTGs, fault current is constant PF
Some WTGs fault current angle varies
considerably through the fault duration
Impedance based relays difficult to use from
WTG end
Overcurrent relays difficult to use from WTG
end
LCD good solution, but requires
communication
Slide 6
Transient Stability Impacts
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•
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•
No unit de-commitments – no problem
De-committed units require inertial
control on WTG unit
Frequency variability will increase
Depending on WTG, voltage stability will
decrease
Slide 7
Transient Stability Limits
•
WTG amounts limited by transient
stability by Railbelt area
-
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Kenai – 30 MW
Anchorage -150 MW
Fairbanks – 100 MW
Total Railbelt penetration as defined by transient
stability – 280 MW
Slide 8
Transient Overvoltages
•
•
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Inverter based WTG islanding results in
transient overvoltages of up to 2.0 pu
Level and duration of transient
overvoltage dependent upon system
connections and controls
Transient overvoltages presents
problems with insulation coordination
Existing arrestors, transformer insulation
requires analysis
Slide 9
Transient Overvoltages
EMTP Simulation of overvoltage following separation
Slide 10
Transient Overvoltages
EMTP Simulation of overvoltage following separation
Slide 11
Voltage Control Methodologies
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•
•
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Grounding transformer
BESS
Arrestor coordination
All require EMTP analysis to ensure
correct operation
Inverter based energy solutions are
limited by SC capacity of Railbelt and its
operating islands
Slide 12
Transient Frequency Stability
•
Following separation from power system
WTG islanded system frequency varies
from 45 to 90 Hz depending on power
factor & load match prior to separation
Slide 13
Voltage Ride Through
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•
•
•
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LVRT capabilities vary a great deal between WTG
manufacturers
No agreement on “single” vs “multiple events” such as
reclosing
FERC defines an event requirement, but does not define
the event as single fault or single fault followed by
restoration and reclose event
FERC standard not applicable in Railbelt
Many islanded systems define reclosing as a required
LVRT event
Sequential events are not considered LVRT events
Slide 14
Voltage Ride Through - GE
Slide 15
Voltage Ride Through
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•
•
•
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To avoid LVRT shutdown, reclosing sequence on all
Chugach 35 kV lines must be changed, including those
from University station
Distribution reclose sequences do not result in LVRT
event at ITSS/FIWF, but do in other parts of the Railbelt
Distribution LVRT events are problematic and will force
Railbelt utilities to make reclosing and protection changes
Transmission faults throughout the Railbelt result in
LVRT events
Unbalanced faults must also be analyzed and specified
for ride-through requirements
0 V ride thru must be required
Slide 16
Wind Analysis
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•
•
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Wind data analysis is the most important
item for integration
Wind analysis defines the amount of
regulation required to integrate wind
Highest cost integration piece in Railbelt
Many different methods for evaluation
No clear method for islanded power
systems
All introduce some risk to utilities
Slide 17
Wind Analysis
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•
•
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Data recorded in 10-minute averages
Short –term ramp rates are generally a
nuisance, but not a costly or technical
concern
WTG cut-out is defined by high winds or
rapid changes in wind direction that force
a wind turbine to shut down
10-minute data typically uses wind
speed, not associated with change in
direction in determining cutout
occurrences
Slide 18
Regulation Requirements
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Upward Regulation
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Amount of regulation required to cover largest expect
loss of wind power
Regulation can be split between hydro and thermal
generation
Hydro cannot supply all of regulation
Downward Regulation
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Amount of regulation required to back down following
the loss of the largest probable load or transmission
line during export
Downward regulation required to prevent widespread
loss of generation following system disturbance
Slide 19
Regulation Requirements
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•
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How much regulation is required?
No clear answer
Independent control areas increase
difficulty and regulation requirement per
control area
Evaluated changes over 10-minute
period, assumed to be fastest scheduling
change for AGC controlled hydro
Slide 20
Regulation Requirements
•
•
Evaluated 30-minute changes – fastest
start time for gas turbine
Evaluated 60-minute changes – fastest
gas nomination schedule change
Slide 21
Slide 22
Slide 23
Power Range
lower
mw
range
[>=]
upper
mw
range
[<]
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
35
40
45
50
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
35
40
45
50
55
10 minutes
20 minutes
30 minutes
40 minutes
50 minutes
60 minutes
Delta between
10 min avg
[counts]
1
0
0
15
6
20
55
101
371
1850
17088
30154
1791
374
122
56
19
11
12
2
1
1
Delta between
10 min avg
[counts]
3
1
8
37
49
70
160
278
889
2938
15916
27347
2850
834
308
158
85
49
45
13
2
3
Delta between
10 min avg
[counts]
7
7
22
77
97
115
244
499
1155
3480
15136
25620
3324
1175
480
224
132
102
75
36
22
9
Delta between
10 min avg
[counts]
10
20
54
112
117
180
346
626
1419
3686
14483
24515
3593
1399
634
294
174
132
116
57
40
26
Delta between
10 min avg
[counts]
16
31
81
146
149
253
410
748
1621
3941
13902
23509
3808
1613
718
344
229
182
131
87
66
44
Delta between
10 min avg
[counts]
27
49
110
174
191
293
489
820
1830
4045
13534
22606
3967
1744
839
398
250
220
171
114
78
77
Slide 24
Slide 25
Slide 26
Slide 27
Slide 28
Regulation Requirement
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•
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Regulation is a system issue, not a wind
project issue
Regulation requirements for one WTG
farm, impacts all wind farms on system
Wind forecasting should incorporate all
WTG projects to determine impact on
system as opposed to individual control
areas
Slide 29
Regulation Requirement
•
•
•
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Final regulation requirement not
determined
Appears extremely variable dependent
upon assumptions for regulation
response time
Minimum appears to be 15 MW for 10
minute case
To cover 60 minute case, appears to be
35-50 MW
Slide 30
Hydro-Thermal Coordination
Slide 31
Hydro-Thermal/Wind Coordination
Slide 32
Hydro-Thermal Coordination
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Wind energy will require hydro energy to
be used non-optimally to provide
regulation support for wind variability
Water “ponded” by storing wind energy
must equal water required for regulation
scheduling to break even
More ponded water than regulation
requirement = benefit
Less ponded water than regulation
requirement = cost
Does not consider cost of wind
Slide 33
Hydro-Thermal Coordination
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Additional regulation and hydro schedule
requirements will decrease efficiency of
combined cycles
Wind may be able to back down simple
cycle enough to “provide its own
regulation” during certain times
Due to gas restrictions – thermal
regulation capacity may not be able to
be resident at one plant or common
supply system location
Slide 34
Hydro-Thermal Coordination
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Hydro units must be dynamically
scheduled to supply regulation
Dynamic scheduling will increase
probability of transmission restrictions on
Kenai
All Kenai hydro and thermal regulation
must reserve transmission capacity
20 MW of hydro regulation reduces
energy transfer limit to 55 MW for
scheduled energy
Slide 35
Hydro-Thermal Coordination
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Positive benefit of transmission
regulation reservation is availability for
spinning reserve
Dynamic scheduling will require revision
to contracts and operating agreements
Dynamic scheduling will require
modification to spinning reserve
compliance
Dynamic scheduling of Bradley by
multiple control centers difficult due to
transmission constraints
Slide 36
Control Agreements
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Control area interchanges must be
dynamically adjusted if sales are made
between control areas unless host utility
is supplying all required regulation
Control area deviations may require new
allowable standards of deviation
between control areas
Slide 37
Frequency Ride Through
•
•
Without Inertial control, wind addition
can lead to increased load-shedding for
unit trips
WTGs must ride meet frequency
capability of existing generation
Slide 38
Fuel Impacts
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Gas Schedules
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$30/mcf penalty for variances over defined amount
Wind variance of only 300 MWh/day results in
variance of 3,700 mcf
Gas penalty - $111,000/day
Gas penalty difficult to distribute between load
variance and wind variance
Gas nomination changes concentrated at one plant
may not be supported by gas delivery/supply system
Slide 39
Curtailment Issues
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Economic Curtailment
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During off-peak hours, curtailment of either wind or
combined cycle plants required
Wind curtailment could be used to provide its own
regulation resource
Curtailment priority among renewable resources
Slide 40
Curtailment Issues
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Transmission Curtailment
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Curtailment required due to transmission constraints
(either energy or regulating capacity)
Curtailment required due to transmission outages
Curtailment required due to contract path interruption
Slide 41
Curtailment Issues
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Generation Curtailment
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Curtailment required due regulation shortage of
generation
Curtailment required due to generation stability (turndown)
Slide 42
Curtailment Issues
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System Curtailment
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Curtailment required due to system upset (load
restoration, storms etc)
Curtailment costs must be defined
Curtailment methodology must be
defined
Curtailment through multiple control
areas must be defined
Use of curtailed energy must be defined
Slide 43
Frequency Control
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Frequency deviations will increase
Frequency variability will increase if units
are de-committed
Frequency impacts can be simulated
Slide 44
Kodiak Hz – Simulation vs Actual
Slide 45
WTG “Options”
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Inertial Control
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Wind Farm Management System
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Simulates machine inertia on power system
Increases frequency stability
Maintains load-shed probability for unit trips
Provides for single point control for curtailment
Provides power ramp control
• Important for restoration
• Curtailment transitions
• Mitigate ramp rates
Droop control (if used for regulation)
Slide 46
WTG “Options”
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LVRT Ride Through
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Option for extended VRT ride thru available on some
units
Voltage Control
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Provides for voltage control mode as opposed to PF
control or constant MVAr mode
New standard in some non-US grids
Not available in all turbines makes/models in US due
to patent restrictions
Slide 47