Frequency Response Provisions
Graham Stein
3 March 2015
Agenda
 Introductions
 Background
 Discussion Topics
 Options for Progression
2
Purpose of the day
 PP14/59 was
presented to the Panel
in November
 Panel members
recommended splitting
the issues for the
purpose of progression
 Workshop was
recommended to help
scope the work
3
Purpose of the day
 Four Grid Code “defects” were outlined in the paper
 Are there other things to consider?
4
Purpose of the day
Workshop Conclusions
Applicable
Objectives
Stop: record the issue
as closed with
reasons why
or
Outline Terms of
Reference to form a
workgroup
Recommendation
Grid Code
Review Panel
Agreed Next Steps
or
Outline scope to
develop proposals for
Consultation
5
Purpose of the day
What we can do today
Recommend undertaking further work which
may result in a Grid Code change
What we can’t do today
Recommend a new market mechanism for
frequency response
Develop requirements for parties not subject to
the Grid Code (eg demand side not connected to
the transmission network)
However, points raised will be recorded
6
Our output could look like…
Issue
Stop
Further
Assessment

B
D
Develop
Consultation

A
C
Form a
Workgroup


….
7
Background
GC0022 Frequency Response Workgroup and Technical Subgroup
GC0022 Frequency Response Workgroup
 GC0022 arose from long running industry discussions
in the Frequency Response Workgroup
 Joint Grid Code/CUSC Workgroup
 Main purpose of Workgroup was to examine market
arrangements
 Grid Code proposals were packaged up in GC0022
 Proposals did not proceed past the draft consultation
stage
 Incorporated the findings of the Frequency Response
Technical Subgroup including
 an assessment of synthetic inertia
 an exploration of Rapid Response
Why Inertia is Important for Frequency
1) Initial Rate of change of frequency limited by stored energy of the rotating mass (ie the size of the inertia)
Frequency
(Hz)
2) Primary Response acts within 10 seconds and sustained for a further 20 to contain frequency deviation
49.2 Hz
-4s
0s
~8s
Time (s)
Power
(MW)
PTemp
(5-10% PNom)
Additional power delivered by synchronous machines – area under the curve is the kinetic energy released by the rotating mass
Power output of decoupled Wind Generation – Ideally such plant should behave like that of a synchronous plant through controlled action
PNom
Recovery in Kinetic Energy following restoration of System Frequency
Primary response delivered by de-loaded machines
PDeload
-4s
0s 2s
12s
Time (s)
10
Frequency
16 October 2014 (1000 MW loss)
49.75
49.75
49.65
49.65
49.55
49.55
09:10…
49.85
09:09…
49.85
09:08…
49.95
09:07…
49.95
09:06…
50.05
09:05…
50.05
09:04…
Frequency (Hz)
Recent Example of a Secured Event
11
Synthetic Inertia
Potential Advantages
Direct replacement for inertia from
synchronous plant
Available without curtailment
Issues
Widely discussed but poorly defined
concept
Active power recovery:

Likely to have value in most power
systems meaning manufacturers might
want to develop it as a standard capability
recovery period for wind turbines
operating just below rated wind speed
(after the synthetic inertial injection)
can result in significant reduction in
active power output causing a double
dip some 10-15s after the initial loss
Control:

Df/dt controllers are noise amplifying
and can fail to operate properly
especially when small time constants
are involved

Response needs to be proportional to
avoid instability
12
Synthetic Inertia: Active Power Recovery
Wind Speed Power Curve p.u.
1.2
Power (p.u.)
1
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
Wind Speed (%)
Worst Case frequency drop
50.5
Frequency (Hz)
50
49.5
49
48.5
48
47.5
0
10
20
30
40
50
60
Time (s)
13
Rapid Frequency Response
Potential Advantages
Standard control philosophy
Extension of existing Balancing
Service
No major technical hurdles
identified
Wide range of plant already
capable
Issues
Potential to disrupt new
technologies
Extension of mandatory
requirement is unpopular
 Perceived potential to restrict
competition
Curtailment required
14
Outstanding Issues
 Frequency response of generators at low load
 Current provisions potentially limit generators’ ability to operate
at low loads by requiring full response capability whilst
operating at or above DMOL. This feature ensures that
response is available when generators are running but
potentially restricts operation at lower loads unnecessarily.
 Frequency Response from other on-site sources
 Current provisions limit the use of alternative solutions (eg onsite batteries, storage or standby units) due to all units being
required to meet the Grid Code rather than the overall output of
the site.
15
Where are we now?
The world has changed since GC0022 was
packaged up
Generation and Demand outlook is different
Commercial Services have been developed
Role of demand expanding
Grid Code governance under review
System Operability Framework developed to
provide a better view of how the behaviour of the
electricity system might evolve
16
The Issues
17
Rapid Frequency Response
a
Issue
Rapid
response for
nonsynchronous
generators
Defect
The current mandatory capability is
not efficient in addressing future
frequency response requirements on
its own. Non-synchronous equipment
does not contribute to system inertia
in the same way as synchronous plant
does.
Faster frequency response will help to
manage the resulting higher rates of
change of system frequency and
reduce the risk of excursions outside
limits. It will reduce the total volume
and cost of Frequency Response and
allow wind turbines, interconnectors
and photo-voltaics to provide more
value to the consumer.
Pros
Reduced
Balancing
Services costs
and therefore
reduced costs
to consumers.
Enhanced
system security
Cons
Increased costs
for generators
which would be
expected to be
reflected in prices
to consumers.
Will require
further
assessment in the
future as the
volume of non
synchronous
plant increases.
There is a
possibility that
synthetic inertia
may be required
in the future
Rapid Frequency Response
What is it?
 Any plant which is insensitive to changes in system frequency and
does not contribute to system inertia to be capable of providing fast
frequency response
 ie applicable to non-synchronous plant (eg wind, interconnectors etc)
 Primary Response to be delivered in the period 0-5s after an incident
(allowing for a 1s delay)
 Low Frequency response to be sustained for 25s
 High Frequency response to be sustained at not less than the
defined initial rate as long as required
 All other aspects of Primary Response unchanged
 eg minimum required volume of 10% of Registered Capacity (RC)
19
Rapid Frequency Response
20
Rapid Frequency Response
Why is it valuable?
Start of frequency deviation
(eg circuit breaker opens)
Period of
highest
rate of
change of
frequency
Response (MW)
Frequency (Hz)
50.0
49.2
0
1
2
5
Time (seconds)
10
System Frequency
Primary Response
Rapid Primary Response
21
Scheduling Frequency Response
3 Generation Scenarios at Low Demand
Scenario
Description
A
Generation matches demand
within the available
regulating range
B
In an example where more
frequency response is
needed, more generators are
required to deliver response.
Eventually you run out of
regulating room.
C
In the absence of other
options, you need to curtail
either wind or other
“inflexible” generation to
solve the problem
22
How do you decide whether to progress?
Ramp Rates and Delay
b
Issue
Clearer delay
and ramp-rate
requirements
Defect
Current provisions leave some
uncertainty over the performance
requirements for generators
delivering frequency response. There
is clear system sensitivity to the
ramping capability of responsive
generation and how quickly response
is initiated. How quickly a generator
meets its primary response
requirement in 10 seconds can be
critical.
Pros
Clearer
ramping
requirements
and initiation
times would
reduce
uncertainty in
calculations of
response
requirements
and in
generator
compliance
assessment.
The ENTSO-E
European
Network Codes
also ask for
these to be
defined.
Cons
Risk of
requirement
being too
onerous,
especially for
certain plant
types
24
Ramp Rates and Delay
 National Grid makes assumptions about how quickly frequency
response is delivered when working out how much is needed
 Our experience has been that response times vary
 Issues have arisen during compliance testing due to varying
interpretations of the Code
25
Low Load Operation
c
Issue
Low Load
Operation
Defect
Current provisions potentially limit
generators’ ability to operate at low
loads by requiring full response
capability whilst operating at or above
DMOL. This feature ensures that
response is available when generators
are running but potentially restricts
operation at lower loads
unnecessarily.
Pros
Facilitates
flexible
operation from
generators and
contributing to
system inertia
and voltage
control
Cons
Requirements
may be complex
to define and
agree.
26
Low Load Operation
27
Alternative on-site sources
d
Issue
Defect
Alternative on- Current provisions limit the use of
site sources
alternative solutions (eg on-site
batteries, storage or standby units)
due to all units being required to meet
the Grid Code rather than the overall
output of the site meeting Grid Code.
Pros
Alternative
ways of
providing
response. This
may however
be addressed
through the
ENTSO-E
Requirements
for Generators
Code
Cons
Potentially limited
application
28
Alternative on site sources
 The Grid Code is not clear on the use of alternative sources to provide
additional frequency response, for example storage
 Could help in cases where technology struggles to provide frequency response
 The Grid Code Connection Conditions place obligations on the
“Generating Unit” which makes it difficult to have separate onsite sources
for the provision of additional Ancillary Services
 RfG could simplify this process as the obligations for Generating Units will
in future be on the basis of a Synchronous Power Generating Module not
the Unit
 The current version of RfG (dated 21 January) only covers Pumped Storage. Storage is
however covered within DCC and is considered as part of a Demand Unit.
 Is there a demand for a change?
29
Discussion
Options to Progress