Ancillary Services, Reliability & Security Assessment: Engineering management of uncertainty
© CEEM 2006
2Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Definitions
Reliability:– Delivered outcome in terms of (un)availability of supply
over the long run (years)Security:– Power system operating strategies to survive near-term
contingencies (unexpected undesirable events)– Specific security concerns include:
Thermal overload, unsatisfactory voltage or frequency (high/low), dynamic instability (transient, oscillatory)
3Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
NEM transmission level reliability target, spot market mechanisms & interventionto meet it(AEMC Reliability Review, 2006)
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NEM forecast & actual low reserve conditions (hours/year) (AEMC Reliability Review, 2006)
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Contributions to unavailability of supply for small end-users (USA data, AEMC, 2006)
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Future state space managedby decentralised decisions
Managing system security in the NEM
Possible futures managedby decentralised (market-based) decisions
Possible futuresmanaged bycentraliseddecisions (NEMMCO)
Presentstate
Growing uncertainty
Time
5 min
Unreachable orunacceptable
futures
Emergency control
7Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Anatomy of a major disturbance(based on IEEE Power & Energy, Sept/Oct 06, p 26)
Satisfactory operating state
Initiating event (contingency)
Remedial action
Cascading outages
System collapse
Major blackout
Stable but in emergency state
Second independent event
Recovery: may take hours
Security management aims to avoid cascading outages & system collapse
8Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Power system security definitions(National Electricity Rules Chapter 4)
Satisfactory operating state:– Frequency in normal operating band (49.9-50.1Hz),
except for brief excursions outside (49.75-50.25Hz) – Voltage magnitudes & line currents within specified limits– All other equipment operating within equipment rating– All plausible fault currents within breaker ratings– The power system is in stable operation
Contingencies (equipment outages):– Credible, eg single generator or network element– Non-credible, eg multiple outages except in abnormal
conditions, eg severe weather, bush fires
9Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Power system security definitions ctd (National Electricity Rules Chapter 4)
Secure operating state:– Currently in a satisfactory operating state– Would return to a satisfactory operating state following
any single credible contingency:Non-credible contingencies can sometimes become credible, eg SA-Vic interconnector double circuit trip during lightning activity
Technical envelope:– Boundary surface of secure operating states:
Which depends on load forecasts, equipment capabilities and their current operating constraints
10Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Power system security tasks & states (National Electricity Rules Chapter 4)
Maintaining power system security:– Keep power system in a secure operating state:
If necessary, modify spot market dispatch constraints to do this
– Return to a secure operating state as soon as possible following a non-credible contingency
– If necessary to maintain security, shed load if frequency is outside the normal operating frequency excursion band (49.75-50.25Hz)
Reliable operating state:– No load has been or is expected to be shed– Reserves adequate for at least next 12 weeks
11Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Power system security responsibilities (National Electricity Rules Chapter 4)
NEMMCO responsibilities:– Monitor & maintain security by developing &
implementing appropriate operating protocols:Maintain a satisfactory operating stateDetermine required reserves (real & reactive) to 12 weeks and assess adequacy of actual reservesInform participants of the outcome of this assessmentContract reserve capability if required
Network service provider responsibilities:– Cooperate with & assist NEMMCO– Provide monitoring, communication & control, load
shedding & restoration schemes12Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Power system security responsibilities ctd(National Electricity Rules Chapter 4)
Market customer (>10MW) obligations:– Provide interruptible load ≥ 60% of expected demand at
NEMMCO specified frequencies from 47 to 49 HzPower system frequency control:– NEMMCO to control by instructing participants:
Generators, loads, network & ancillary services (generators to have governor & protection systems)
Power system voltage control:– NEMMCO to control by instructing participants:
Generator voltage regulators, shunt capacitors & reactors, static VAR compensators
13Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Power system security responsibilities ctd(National Electricity Rules Chapter 4)
Protection of power system equipment (NEMMCO):– Calculate fault levels & ensure they are within breaker
interruption capacity– Take advantage of short term equipment ratings– Coordinate protection operation & manage risks during
protection outagesPower system stability coordination (NEMMCO):– Design, arrange installation & test effectiveness of power
system stabilisers
14Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Power system security declarations (National Electricity Rules Chapter 4)
NEMMCO declaration of security conditions:– Low reserve conditions:
Reserves out to 12 weeks below reserve standards
– Lack of reserve level 1:Non-secure state following a credible contingency
– Lack of reserve level 2:Involuntary load shed following a credible contingency
– Lack of reserve level 3:Involuntary load shedding occurring or about to occur
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Power system security projections (National Electricity Code Chapter 4)
NEMMCO demand forecasts (indicative):– Daily forecasts to one week in 30 min intervals– Weekly forecasts to 2 years with daily profile– Forecasts with 10% probability of exceedence to be
used for assessing reserve requirementsProjected assessment of system adequacy:– Demand & supply-side forecasts:
Daily projection to one week (STPASA)Weekly projection to two years (MTPASA)
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Power system security projections ctd(National Electricity Code Chapter 4)
Statement of opportunities (SOO):– Prepared annually by NEMMCO to assess future need
for additional generation, demand management or network augmentation
Annual National Transmission Statement:– Identifies major transmission flow paths– Projects pattern of generation & demand– Assesses adequacy of transmission capacity
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Dispatch, Pre-dispatch, PASA, SOO & ANTS(source: NEMMCO)
0 day 1 day 2 week 1 month 1 year 1 year 2
Medium Term PASA (2 yr, daily peak)
Pre-dispatch, re-bid & final dispatch schedule
Short Term PASA (7 days, 30 min res, 2hr update)
SOO & ANTS (10 yr)
• ST & MT Projected Assessment of System Adequacy support reserve assessment & participant operating decisions. ST PASA projects region demand & reserve for 7 days @ 30 min resolution, updated every 2 hours. MT PASA projects region daily peak demand & reserve for 2 yrs, updated weekly.
• Statement of Opportunities (SOO) & Annual National Transmission Statement (ANTS) are intended to inform generation, demand & network investment decisions (10 year horizon, issued annually)
18Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
MTPASA example (www.nemmco.com.au )
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
(DSP = demand side participation)
19Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
PASA & reserve contracts
PASA
•Energyconstraints•Demandforecasts•Networkcapacity
Registration ofavailable capacities
Day-ahead Offers & bids
Pre-dispatchthen
dispatch
Invitation to provide more capacity
Purchase of more capacity
NEMMCO
Expectedinadequacy
Purchased capacity offered to market at price that would have otherwise applied (usually VOLL)Available
capacity
SettlementsPayment for purchased capacity
(long term expected USE < 0.002%)
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SOO example - outlook for Victoria & SA: Performance indicator: Low Reserve Capacity (LRC)(NEMMCO SOO, 2005)
Note: uncertainty in future supply-demand balance is inevitable in a restructured industry with decentralised decision-making
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SOO: projected NEM-wide reserve margin: (installed gen - peak demand)/(installed gen) (NEMMCO SOO, 2005)
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NEM frequency control ancillary servicesFrequency management - small deviations:– Maintain frequency within normal band & control time error– Two markets (raise & lower regulation) from 10/01
Frequency management - large deviations:– Large step changes in demand– Loss of largest single generator– Multiple contingencies– Six markets from 10/01: 6 sec; 60 sec; 5 min raise & lower
23Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Supply-demand balance in the electricity industry
Frequency is a measure of supply-demand balance:– Always varying due to fluctuations in energy flows
Thermalpower stations
Other, eg wind farms
Hydrogenerators
Industrial
Commercial
Residential
Generator input power Load electrical powerplus network losses
+ _
24Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Continuous frequency control
GenerationControl system
Powersystem
Electricalpower
Electricalpower
Tie flow to anotherpower system
Tie flow to anotherpower system
Frequencymeasurement
GeneratorPower output
Tie flowmeasurement
Turbine-generators
(based on Wood & Wollenberg Fig 9.2)Controlsignalsto turbinepower
25Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
A generator responding to dispatch & small disturbance frequency controlenergy
target for nextspot market
linear rampfrom previous
ave power level
∑generator
powerset-point
actualgeneration
frequencyerror
timeerror
AGCprocessing
&filtering
shaftspeed
(frequency)errors
∑+
-
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A generator tracking five-minute dispatch targets with AGC raise/lower bounds
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Large disturbance frequency control:loss of NSW 660 MW Generator (source: NEMMCO)
Maintain frequency in tolerance band > 49.5 Hzby local governor action
50.0 Hz
49.9 Hz
49.5 Hz
Maximum Power Input = 630 MW (net of unit auxiliary load)
Load relief is 200 MW for a typical minimum load of 10 GW
Frequency control capability requirement = R
R6s (raise) = 430 MW
R5m (raise) = 630 MW less any load shedding included in 6 sec response which has not been restored
Return to normal frequency band >49.9 Hz within 5 min by AGC
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Indicative AS response to a unit outage
MW error 5 minutes
60 secondresponse
5 minutedispatchresponse
6 secondresponse
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NEM frequency tolerance bands
State Frequ ency band (Hz)
Normal 49.85 Š 50.15 (99 % of t ime )49.75 Š 50.25 (1% of t ime )
Single gene rato rcontingen cy
49.5 Š 50.5
Other credib lecontingen cy
49.0 Š 51.0
Em ergen cy 47.0 Š 52.0
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Distribution of frequency in the NEM, June 2003(Reliability Panel Annual Report, 2002-3)
0.00
5.00
10.00
15.00
20.00
25.00
49.90 49.92 49.94 49.96 49.98 50.00 50.02 50.04 50.06 50.08 50.10
Frequency (Hz)
Occurence (%)
Target frequency band (normal)
31Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Frequency events outside the normal operating band in the NEM due to contingencies, 2002-03(Reliability Panel Annual Report, 2002-03)
0
4
8
12
16
20
<10 <20 <30 <40 <50 <60 <70 <80 <90 <100 <110<120<130 <140<150<250<300 >300
Duration outside normal operating band (seconds)
Number of events
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~600MW
Transgrid CT failure @ 2142 13/8/04 led to 3100 MW gen trip. Frequency fell to 48.9Hz, ~2100 MW load shed in NSW, Qld, Vic & SA
~900MW
~600MW
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NEM energy revenue, 13/8/04 (IES)
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NEM FCAS revenue 13/8/04 (IES)
35Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Network Control Ancillary Services (NCAS)Voltage control - continuous: – NEC requires tap changers
Voltage control - contingency:– Reactive power resources for planned worst case
conditions– Emergency schemes for plausible multiple
contingenciesStability control– NEC requires generators to install stabilisers
To enhance small & large disturbance stability
36Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Network Control Ancillary Services (continued)
Network loading contingency control:– To control transmission line flows– To permit full utilisation of transmission lines subject to
equipment & security constraints
System Re-start Ancillary ServicesPower station self-start capabilityEarly restoration of supply to major cities
37Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Australian management of severe network contingencies:NSW bushfires Dec 2002; lines with multiple trips shown in red
38Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Sydney region voltages during 2002 bushfire outages:managed by under-voltage relays shedding load
39Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
A distribution network perspective on ancillary services
Transmission level ancillary services have little impact on distribution network QOS:– Voltage regulation, waveform purity,
phase balance & supply availabilityDistribution level ancillary services may also address transmission level QOS:– e.g. voltage, frequency & security services
Thus distribution-level AS may have greater value than transmission level AS:– Not yet reflected in National Electricity Rules
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Quality of supply in distribution networks
Quality of supply attributes (QOS):– Voltage, frequency, waveform purity– Supply availability
Practical network can’t achieve perfect QOS:– Supply availability can vary widely within distribution
networks– Poor QOS can cause electrical equipment to
malfunction– Customer equipment can affect QOS
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Energy density & reliability of NSW Distributors (IPART, 1996/97)
050
100150200250300350400450
MWh percircuit km
Ave outagetime (min/yr)
Australian InlandEnergyAdvance Energy
Northpower
Great SouthernEnergyIntegral Energy
EnergyAustralia
42Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Average reliability in EnergyAustralia regions(EnergyAustralia Electricity Supply Standards, 1998)
0
1
2
3
4
5
6
7
Hrs/yr Interruptions
CBD, Inner SuburbsEastern SuburbsLake MacquarieNewcastleSouthern SuburbsNorthern SuburbsMaitlandCentral CoastMusswellbrook
43Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
5-year average reliability in EnergyAustralia regions(EnergyAustralia Electricity Network Standards, 2004)
44Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
IPART’s recommended guaranteed customer service standards (IPART, 2004)
Compensate customers on application if the number of outages per financial year exceed:– For EnergyAustralia & Integral:
9 for customers on urban feeders15 for customers on rural feeders
– For Country Energy & Australian Inland Energy:12 for customers on urban feeders20 for customers on rural feeders
Compensate all DNSP customers on application if an individual outage exceeds 12 hoursUp to a limit of 4 payments per year per customer
45Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Average voltage dip events in EnergyAustralia service territory(EnergyAustralia Electricity Supply Standards, 1998)
0
10
20
30
40
50
60
<30% 30-50% 50-70% 70-80% 80-90%
Events/yr
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One piece of electrical equipment may interfere with another
“ There goes that damn electric chair again ! ”
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Possible design enhancements for ancillary services & security
Balance between engineering & commercial management of uncertainty in the short term:– A closer approximation to nodal pricing with greater
demand-side participation in NCAS– A clearer boundary between FCAS & the energy spot
market, with greater demand-side participation in FCASBalance between engineering & commercial management of uncertainty in the long term:– Coordinated, system-wide derivative markets with active
demand-side participation could partially substitute for MTPASA, SOO & ANTS
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ConclusionsAncillary & security services are essential in a competitive electricity industry:– Required to maintain availability & quality of supply– Critical in determining the need for investment
AS most important at consumer nodes:– Primarily distribution rather than transmission issue– AS presently dealt with at the wholesale level:
Bias towards large participants
Australian approach to AS is still evolving:– Unresolved issues include boundary problems– Distributor & end-user roles not yet acknowledged
49Ancillary Services & Security Assessment: Engineering management of uncertainty © CEEM 2006
Many of our publications are available at:www.ceem.unsw.edu.au
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