Definitions - University of New South Wales

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)


NEM transmission level reliability target, spot market mechanisms & interventionto meet it(AEMC Reliability Review, 2006)


NEM forecast & actual low reserve conditions (hours/year) (AEMC Reliability Review, 2006)


Contributions to unavailability of supply for small end-users (USA data, AEMC, 2006)


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


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


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


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


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


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


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


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


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)


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


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)


MTPASA example (www.nemmco.com.au )

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

(DSP = demand side participation)


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%)


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


SOO: projected NEM-wide reserve margin: (installed gen - peak demand)/(installed gen) (NEMMCO SOO, 2005)


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


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

+ _


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


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

∑+

-


A generator tracking five-minute dispatch targets with AGC raise/lower bounds


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


Indicative AS response to a unit outage

MW error 5 minutes

60 secondresponse

5 minutedispatchresponse

6 secondresponse


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


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)


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


~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


NEM energy revenue, 13/8/04 (IES)


NEM FCAS revenue 13/8/04 (IES)


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


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


Australian management of severe network contingencies:NSW bushfires Dec 2002; lines with multiple trips shown in red


Sydney region voltages during 2002 bushfire outages:managed by under-voltage relays shedding load


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


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


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


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


5-year average reliability in EnergyAustralia regions(EnergyAustralia Electricity Network Standards, 2004)


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


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


One piece of electrical equipment may interfere with another

“ There goes that damn electric chair again ! ”


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


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


Many of our publications are available at:www.ceem.unsw.edu.au

Definitions - University of New South Wales

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