IEEE Power & Energy Magazine - November/December 2019 - 64

service provider (Figure 5). For example, it was proposed
that the previous responsive reserve service (RRS) be disaggregated into two pieces. The first is a new RRS that applies
only to the period directly after occurence of a contingency
until frequency is stabilized but not corrected (e.g., 30 s). The
second is the ERCOT contingency reserve services, which
specifically covers the time after frequency is stabilized until
the frequency and area control error have been corrected
(e.g., 10 min). The new RRS is further split into FFR service (FFRS) and primary frequency response (PFR). FFRS
is characterized by its ability to convert reserve capacity into
energy or curtail energy consumption extremely quickly
(15 cycles, a quarter of a second) and sustain that response for
15 min if needed. This allows the independent system operator to get what it truly needs (energy with little delay after
a disturbance), rather than designing the product in only the
traditional way around a conventional turbine governor. One
final evolution is that the system requirements for many of
these services are dependent on one another. For example,
the requirement of how much RRS is needed depends on

NPRR 863

Current Framework
Regulation
157-687 MW

Regulation
157-687 MW

RRS

FFR
Load
Resources on UFR
RRS
1) PFR
2) Load Resources on
Underfrequency Relay (UFR)
3) 10-min Ramp
2,300-3,200 MW

PFR
2,300-3,200 MW
ERCOT
Contingency Reserve
Service (ECRS)
10-min Ramp
Load Resources May
or May Not Be on UFR
508-1,644 MW

Nonspin
967-2,361 MW
Overall A /S: 3,807-5,958 MW∗

how much system inertia ERCOT has. In ERCOT's case,
having more realistic service definitions that achieve system
needs and characterizing these needs accurately offer the
potential for incentives that continue to motivate sellers to
provide a better service at lower cost.
European transmission system operators are also aware
of the changes needed when large rotating mass units disappear from the grid. Even if there is no clear view of the
services required in the future, there is a belief that technology will be up to the task. Considerable research and pilot
projects have been conducted on FFR, synthetic inertia, and
better use of demand and renewable energy sources in countries such as Ireland, Spain, Denmark, and Germany.
As the system shifts toward an increasingly inverter-connected fleet, there is an increased focus on developing incentive compatibility around system services across operational,
planning, and investment time frames. However, certain services may be better suited than others for being procured
through market frameworks. For example, inertia for interconnection frequency support can be provided throughout the

Nonspin
0-1,181 MW

No Change
FFR
* Triggered at 59.85 Hz and Full Response in 15 Cycles
* Once Deployed, Sustain for up to 15 min;
Once Recalled, Restore Within 15 min
PFR
* PFR-Capable Capacity Reserved on Generators or
Controllable Load Resources (CLRs)
* Minimum 1,150-MW Must Be Provided by Resources
Capable of PFR
Load Resources on UFR
* Triggered at 59.70 Hz and Full Response in 30 Cycles
* Sustain Until Recalled; Once Recalled, Restore Within 3 h
* Beyond the Minimum PFR, up to 60% of Total RRS
Can Come From Load Resources on UFR or FFR
Generation
* Online or Offline Capacity That Can Be Converted to
Energy Within 10 min
* Dispatched by SCED
Load Resources (UFR Not Required)
* Up to 50% of ECRS Capacity Can Come From Load
Resources With or Without UFR
* Once Deployed, Must Respond Within 10 min
Restoration Within 3 h
No Protocol Changes
* Proposed Methodology for Nonspin Reserve Service
Quantities in This Framework-Quantities Computed Using
2018 A /S Methodology Are Reduced by ECRS Quantities
Overall A /S: 3,807-5,958 MW

figure 5. The proposed ERCOT ancillary service framework changes. A/S: ancillary services; NPRR: Nodal Protocol
Revision Request; SCED: security-constrained economic dispatch.
64

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