Frequency Response Requirements Basic Concepts FRR Basic Concepts- Green.pdf · of under-frequency...
Transcript of Frequency Response Requirements Basic Concepts FRR Basic Concepts- Green.pdf · of under-frequency...
California ISO PublicCalifornia ISO Public
Frequency Response Requirements – Basic
Concepts
Irina Green
Regional Transmission Senior Advisor, California ISO
WECC PMWG, May 8-10, 2018
California ISO Public
Continuous Supply and Demand Balance
Slide 2
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Frequency Regulation –Governor Droop
Slide 3
Each generating unit with
governor control contributes to
system regulation according to
the overall gain set in the
governor control loop
Each governor is acting to
control speed, increas power
when frequency is below the set
point
Droop = Change in percent
frequency per change in percent
output, e.g.,
f drops to 59.9 Hz, with 5% droop
setting, unit responds with ([60-
59.9]/60)/0.05 = 3.33% of rated
power
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Frequency with a Loss of a Resource
Slide 4
nadir
settling
frequency
System inertia is the amount of kinetic energy stored in all
spinning turbines and rotors in the system, decreases with more
inverter-based generation. Nadir will be lower with lower inertia
Settling frequency depends on the headroom of the generators
with responsive governors and on governor droop
California ISO Public
Governor Response and Frequency Regulation
Governor response has enormous impact on frequency
regulation
Frequency regulation is largely impacted by operation (control
modes, load points, etc.)
Poor system frequency regulation can lead to load shedding,
generator trips
For meaningful studies of off-nominal frequency events, it is
essential to properly characterize the response of each
generator
Governors may be disabled, or operating at limit
Droop (governor gain) may be nonlinear, may be affected by
ambient conditions, it has deadband
Inverter-based resources need to have special technical
controls to be able to provide frequency regulation
Slide 5
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Non-summer months – net load pattern changes significantly
starting in 2014
Slide 6
Net load is the load that must be served by dispatchable resources
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Over-generation occurs when there is more generation and imports
into a BAA than load and exports
Prior to Over-Generation Conditions
System Operators will exhaust all efforts to dispatch
resources to their minimum operating levels
Utilize all available DEC bids
De-commit resources through real-time unit commitment
Arrange to sell excess energy out of market
Dispatch regulating resources to the bottom of their
operating range
Send out market notice and request Scheduling
Coordinators to provide more DEC bids
Slide 7
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Negative real-time energy market prices (ISO must pay internal or external entities to consume more or produce less power)
Area Control Error greater than zero and system frequency greater than 60 Hz
Difficult to control the system due to insufficient flexible capacity
Inability to shut down a resource because it would not have the ability to restart in time to meet system peak
Inability to quickly arrest frequency decline (less inertia) and stabilize the system (frequency response) following a disturbance
May have to commit more resources on governor control
May result in curtailment of resources that cannot provide frequency response
Slide 8
Operational concerns during over-generation conditions
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NERC Standard BAL-003. Frequency Response Obligation (FRO)
Slide 9
Frequency Response Measure (FRM)
FRO for the Interconnection is established in BAL-003-1
Frequency Response & Frequency Bias Setting Standard
For WECC FRO is 840 MW/0.1Hz
Balancing Authority FRO allocation
For the CAISO, FRO is approximately 30% of WECC FRO (252
MW/0.1HZ)
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Frequency Response Metrics
Slide 10
• Frequency Bias Setting (FBS) MW/0.1Hz - a value set into a
Balancing Authority Area Control Error (ACE) algorithm that
allows the Balancing Authority to contribute its frequency
response to the Interconnection
• Frequency Response Obligation (FRO) MW/0.1Hz - the
Balancing Authority’s contribution to the total aggregate
Frequency Response needed for reliable operation of an
Interconnection
• Frequency Response Measure (FRM) MW/0.1Hz – the
change in the Net Actual Interchange on tie lines with its
adjacent Balancing Authorities divided by the change in
Interconnection frequency. Calculated from Single Event
Frequency Response Data
California ISO Public
Slide 11
Other Frequency Response Metrics
The headroom is defined as a difference between the maximum
capacity of the unit and the unit’s output.
To have an adequate frequency response, sufficient
headroom is needed
Kt - the ratio of generation that provides governor response to all
generation running on the system
It is used to quantify overall system readiness to provide
frequency response.
Kt is defined as the ratio of power generation capability of
units with governors to the MW capability of all generation
units.
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Primary Frequency Response
Slide 12
Governor response
AGC
Operator actions
Point C –
nadir
Point B –
settling
frequency
Nadir
needs to
be higher
than set-
point for
UFLS (59.5
Hz)
California ISO Public
Mitigating Measures Needed if any Violations of the
BAL-003 Standard Occur Post contingency frequency nadir encroaches the first block
of under-frequency load shedding relays set-point (59.5 Hz)
CAISO’s Frequency Response Measure (FRM) is less than
its Frequency Response Obligation
Headroom or unloaded synchronized capacity is incapable
of meeting the CAISO’s FRO
Insufficient generators with governors cannot be
synchronized to the system due to high levels of non-
dispatchable generation
Recent studies and operational experience at the CAISO
showed that although WECC has sufficient frequency
response, response from the CAISO may be below its FRO
for some contingencies under some conditions.
Slide 13
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CAISO Frequency Response Initiative Phase 1
Stronger governor and control requirements to increase ISO assurance that generators with governors are not inhibiting their response.
In 2016 FERC accepted tariff revisions requiring participating generators with governors to revise their governors settings
FERC accepted agreements for the ISO to procure transferred frequency response, i.e. insurance, from Bonneville Power Authority and the City of Seattle
FERC has a proposed rule to require all newly interconnecting resources, including non-synchronous resources, to have the capability to respond to provide frequency response
ISO has started phase 2 of its stakeholder process to explore explicit procurement of primary frequency response
Slide 14
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CAISO Frequency Response Initiative Phase 2
Phase 2 of frequency response initiative considered market
based enhancements based on operational needs
Currently CAISO procures additional transferred frequency
response from other Balancing Authorities
Transferred frequency response is included in the CAISO
frequency response measure
No need for additional enhancements at this time
Slide 15