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

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Frequency Regulation –Governor Droop

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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

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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

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Non-summer months – net load pattern changes significantly

starting in 2014

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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

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California ISO Public

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

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Operational concerns during over-generation conditions

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NERC Standard BAL-003. Frequency Response Obligation (FRO)

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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

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• 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

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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

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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)

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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.

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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

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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

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Questions/Comments?

igreen@caiso.com

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