PB Power. Determining Optimum Spinning Reserve 2001 CARILEC Engineers Conference July 25th - 27th, 2001 Roger Blackman Barbados Light & Power Pedro J

PB PowerPB Power

PB PowerPB Power

Determining OptimumDetermining Optimum Spinning ReserveSpinning Reserve

2001 CARILEC2001 CARILEC

Engineers ConferenceEngineers ConferenceJuly 25th - 27th, 2001July 25th - 27th, 2001

Roger BlackmanRoger BlackmanBarbados Light & PowerBarbados Light & Power

Pedro J CastroPedro J CastroPB PowerPB Power

PB PowerPB PowerBarbadosBarbadosLight & PowerLight & Power

• Began operation on June 17th, 1911.Began operation on June 17th, 1911.• Wholly owned subsidiary of Light & Wholly owned subsidiary of Light &

Power Holdings.Power Holdings.• 115 / 230 V – 50 Hz supply.115 / 230 V – 50 Hz supply.• 101,300 customers at the end of 2000.101,300 customers at the end of 2000.• 185.5 MW of installed capacity.185.5 MW of installed capacity.• Peak load of 128 MW.Peak load of 128 MW.• Electricity sales in 2000 of 704 GWh.Electricity sales in 2000 of 704 GWh.

PB PowerPB Power

PB POWERPB POWER

• A Parsons Brinckerhoff companyA Parsons Brinckerhoff company• Combines the Combines the experience and expertise of experience and expertise of

four leading consultancy firms: four leading consultancy firms: – Merz and McLellan (UK)Merz and McLellan (UK)– Kennedy & Donkin (UK)Kennedy & Donkin (UK)– Design Power (NZ)Design Power (NZ)– PB Energy Services (US)PB Energy Services (US)

• Over 1000 professionalsOver 1000 professionals providing providing eengineering and management consultancy ngineering and management consultancy services for the power industry world-wideservices for the power industry world-wide

PB PowerPB Power

ObjectivesObjectives

• To present the technical issues To present the technical issues affecting spinning reserve policy.affecting spinning reserve policy.

• To present the economic issues To present the economic issues affecting spinning reserve policy.affecting spinning reserve policy.

• To outline the methodology used in To outline the methodology used in determining optimum spinning reserve. determining optimum spinning reserve.

• To summarize the results of the BL&P To summarize the results of the BL&P spinning reserve study.spinning reserve study.

PB PowerPB Power

BackgroundBackground

• Increasing customer expectationsIncreasing customer expectations

• Existing spinning reserve policyExisting spinning reserve policy

• Service interruptionsService interruptions

• Generation expansion plansGeneration expansion plans

• Existing U/F relay settingsExisting U/F relay settings

• Proposal for a 9.2 MW wind farmProposal for a 9.2 MW wind farm

PB PowerPB Power


Technical IssuesTechnical Issues

PB PowerPB PowerSystem Frequency System Frequency DynamicsDynamics

• System Stored Energy

loadgenmech PPdt

dE loadgen

mech PPdt

dE

PB PowerPB Power

Where,Where,df/dtdf/dt = Rate of change in frequency= Rate of change in frequencyffoo = Base frequency, 50Hz= Base frequency, 50Hz

HH = Inertia = Inertia cconstant onstant oof f ssystemystemPPgengen = Active = Active ppower ower ggenerationeneration

PPloadload = Active = Active ppower ower ddemandemand

SSratedrated = Total MVA = Total MVA rrating ating oof f rrotating otating pplantlant

• The Swing Equation

System Frequency System Frequency DynamicsDynamics

rated

loadgen

S

PP

H

f

dt

df

20

rated

loadgen

S

PP

H

f

dt

df

20

PB PowerPB PowerFactors Affecting Factors Affecting Frequency DecayFrequency Decay

• Overload (Overload (P ))

• System System iinertia (nertia (H))

• Frequency Frequency ddependency ependency oof f lload (oad (d))

• Frequency Frequency ccontrol ontrol ssystems:ystems:- governor action (spinning reserve)governor action (spinning reserve)- load sheddingload shedding

rated

loadgen

S

PP

H

f

dt

df

20

rated

loadgen

S

PP

H

f

dt

df

20

PB PowerPB Power

• Overload is the difference between the Overload is the difference between the active power demand and the active active power demand and the active power generated, as a percentage of power generated, as a percentage of power generation, i.e.power generation, i.e. P=(Pgen – Pload)/ Pgen

• The greater the overload, the greater The greater the overload, the greater the rate of frequency decaythe rate of frequency decay

• Small islanded systems: overloads tend Small islanded systems: overloads tend to be largerto be larger

Overload InfluenceOverload Influence

PB PowerPB Power

Overload InfluenceOverload Influence

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Time (seconds)

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(H

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50% Overload

30% Overload

10% Overload

100% Overload

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50% Overload

30% Overload

10% Overload

100% Overload

H=4s, d=2H=4s, d=2

PB PowerPB Power

• The rotating plant of the system will tend to maintain its rotational speed due to its moment of inertia (H)

• Determines initial rate of decay of frequency for a given overload

• The smaller the inertia of the rotating plant, the faster the decay in frequency

• Small islanded systems have relatively small system inertia

Inertia InfluenceInertia Influence

PB PowerPB Power

Inertia InfluenceInertia Influence

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H = 2s

H = 7sH = 4s

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(H

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H = 2s

H = 7sH = 4s

d=2, d=2, P=50%P=50%

PB PowerPB Power

• As system frequency deAs system frequency decayscays, system , system demand decreases.demand decreases.

• This effect due primarily to the dynamic This effect due primarily to the dynamic behaviour of motor loadsbehaviour of motor loads

• Load Reduction Factor :Load Reduction Factor :

Load Self-regulation Load Self-regulation InfluenceInfluence

00 f

fd

P

P

load

load

00 f

fd

P

P

load

load

PB PowerPB PowerLoad Self-regulation Load Self-regulation InfluenceInfluence

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Time (seconds)

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d = 2.0

d = 3.0

d = 1.2

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d = 2.0

d = 3.0

d = 1.2

PB PowerPB PowerFrequency Control Frequency Control ToolsTools

• Governor Action – automatic control of Governor Action – automatic control of power generation to match system load power generation to match system load and maintain frequency.and maintain frequency.

• Under-frequency Under-frequency lload oad sshedding – hedding – automatic shedding of discrete loads to automatic shedding of discrete loads to prevent total system collapse.prevent total system collapse.

PB PowerPB Power

Power-FrequencyPower-Frequency Control Loop Control Loop

Governor ActionGovernor Action

TurbineTurbineDroop Droop GainGain

CompensatorCompensator Valve Valve ActuatorActuator

Shaft Shaft InertiaInertia

TransducerTransducerGenerator Load TorqueGenerator Load Torque

Turbine TorqueTurbine Torque

SpeedSpeedSpeed Speed SignalSignal

Speed Speed Set PointSet Point

Power Power Set PointSet Point

PB PowerPB Power


• The governor droop is the percentage The governor droop is the percentage variation in frequency to which the variation in frequency to which the governor responds by effecting a 100% governor responds by effecting a 100% change in power outputchange in power output

• The governor compensator is a filter of The governor compensator is a filter of the input signal that allows for tuning of the input signal that allows for tuning of governor response dynamicsgovernor response dynamics

PB PowerPB Power


System Response, Jan 25, 2001 - 2 MW Generation LossSystem Response, Jan 25, 2001 - 2 MW Generation LossSteamSteam vs vs LSD LSD rresponsesponsee

48.848.8

4949

49.249.2

49.449.4

49.649.6

49.849.8

5050

50.250.2

00

33

77

1010

1313

1616

2020

2323

2626

2929

3333

3636

3939

4242

4646

SecondsSeconds

Fre

qu

ency

Fre

qu

ency

PB PowerPB PowerUnderUnder--frequency frequency Load SheddingLoad Shedding

• UFLS is a last resort, emergency actionUFLS is a last resort, emergency action

• Emphasis on saving the system from Emphasis on saving the system from collapsecollapse

• In small isolated systems:In small isolated systems:– Overloads tend to be largerOverloads tend to be larger– System Inertia is smallerSystem Inertia is smaller– More drastic, faster action is requiredMore drastic, faster action is required– 80-100% of load subject to shedding in 80-100% of load subject to shedding in

principleprinciple


Design Considerations:Design Considerations:• Spinning ReservesSpinning Reserves

– LevelLevel– DistributionDistribution

• Load Shedding ParametersLoad Shedding Parameters– Maximum anticipated overload Maximum anticipated overload – Amount of load to be shedAmount of load to be shed– Frequency thresholdsFrequency thresholds– Step size and number of stepsStep size and number of steps– Time delaysTime delays– Priorities and distributionPriorities and distribution


• Generating plant is highly sensitive to Generating plant is highly sensitive to frequency dropfrequency drop– Low pressure turbine stagesLow pressure turbine stages– Motor driven auxiliariesMotor driven auxiliaries– Mechanical fatigue is cumulativeMechanical fatigue is cumulative

• Transient minimum frequencyTransient minimum frequency thresholds thresholds• Recovery frequency bandRecovery frequency band

– Governor action - Spinning reservesGovernor action - Spinning reserves– System dispatcher actionSystem dispatcher action

• Manual increase of load sheddingManual increase of load shedding• Start-up additional generationStart-up additional generation


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Example of over-shedding

Minimum Recovery Frequency

Example of under-shedding

Maximum Recovery Frequency

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Example of over-shedding

Minimum Recovery Frequency

Example of under-shedding

Maximum Recovery Frequency


Number and size of shedding stages:Number and size of shedding stages:

• Many & Small vs. Few & LargeMany & Small vs. Few & Large– Many Small StagesMany Small Stages

• Avoids overAvoids over--shedding shedding • Too slow for large overloadsToo slow for large overloads• Tends to inhibit system recoveryTends to inhibit system recovery

– Few Large StagesFew Large Stages• OverOver--shedding may occurshedding may occur• Faster corrective action for large overloadsFaster corrective action for large overloads


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H=4s, d=2, H=4s, d=2, P=20%P=20%

PB PowerPB Power

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H=4s, d=2, H=4s, d=2, P=50%P=50%

UnderUnder--frequencyfrequencyLoad SheddingLoad Shedding

PB PowerPB Power


Study MethodologyStudy Methodology

MethodologySelect Spinning Reserve Policy

Select Demand Level From Load Duration Curve

Produce Despatch To Meet Demand Level

Model System & Simulate Unit Trip.Perform Transient Stability Analysis

Calculate Energy Lost

Calculate Total Energy Lost

Calculate Annual Cost Of Unserved Energy

Calculate Despatch Costs

Find Optimum Spinning Reserve

PB PowerPB Power

PB PowerPB Power

MethodologyMethodology

• Select SpinningSelect Spinning Reserve Policy Reserve Policy – A spinning reserve policy determines the A spinning reserve policy determines the

amount of extra capacity of despatched amount of extra capacity of despatched generation over and above the load generation over and above the load requirement at any given time.requirement at any given time.

– Define several spinning reserve policies for Define several spinning reserve policies for testing.testing.

PB PowerPB Power


• Select Select a number of discreet da number of discreet demand emand llevelsevels from the load duration curve from the load duration curve

• Produce a generation despatch for each Produce a generation despatch for each load levelload level

• For each load level and despatch, conduct a simulated trip of each of the despatched generators, using a dynamic computer model e.g. ETAP

• Obtain the amount of load shed from model, for each generator trip

PB PowerPB Power

• For each study the amount of load shed will be obtained, and this translated into the value of energy lost:

Load Shed x Mean Time to Restore Supply x Probability of trip

• The total annual energy lost for each spinning reserve scenario is equal to:

Energy lost for each load condition x Time condition prevails


PB PowerPB Power

• Calculate the annual cost of unserved energy (COUE) as a result of spinning reserve strategy:

Specific COUE x Total Annual Energy Lost

• Calculate the despatch costs for a given spinning reserve policy, by adding the despatch costs for various demand levels considered.


PB PowerPB Power

• Spinning Reserve will be at its economic optimum when the despatch costs plus the COUE is at its minimum:


Demand and Supply Costs

LOLE

Cost $

Demand $ Supply $ Total

Optimum

PB PowerPB Power


Spinning Spinning Reserve Reserve (MW)(MW)

Cost of Cost of Unserved Unserved EnergyEnergy

Load Shed Load Shed (MW)(MW)

d$(SR)d$(SR)dSRdSR

d$(UE)d$(UE)dSRdSR

PB PowerPB Power


Spinning Reserve StudySpinning Reserve Study ResultsResults

PB PowerPB PowerSummary Of ResultsSummary Of ResultsOptimumOptimum Spinning Reserve Spinning Reserve - 2001- 2001

<50%

50%-5

5%

55%-6

0%

60%-6

5%

65%-7

0%

70%-7

5%

75%-8

0%

80%-8

5%

85%-9

0%

90%-9

5%

95%-1

00%

0MW

2MW

4MW

6MW

8MW

10MW

12MW

System Demand

Sp

inn

ing

Res

erve

PB PowerPB PowerSummary Of ResultsSummary Of Results OptimumOptimum Spinning Reserve Spinning Reserve - 2003- 2003

0MW

2MW

4MW

6MW

8MW

10MW

12MW

14MW

16MW

System Demand

Sp

inn

ing

Re

se

rve

PB PowerPB Power

• Spinning Reserve:• Spinning Reserve should be spread evenly among

the ‘large units’.• The economic optimum spinning reserve in 2001

is between 0 and 2 MW for demand levels > 70 MW, and 4 MW for demand levels < 70 MW.

• The economic optimum spinning reserve after installation of the 30 MW Low Speed for demand levels < 55% is between 8 and 10 MW.

• The installation of a 9 MW wind farm will not require any additional spinning reserve.

Summary Of ResultsSummary Of ResultsFrom BL&P Spinning Reserve StudyFrom BL&P Spinning Reserve Study

PB PowerPB Power

• Underfrequency Load Shed Scheme:• The existing load shed scheme should be modified

to shed larger blocks of load. There should be around 5 blocks each configured to shed between 6% and 9% of system load.

• Time delays which are presently associated with some of the underfrequency relays should be removed.


PB PowerPB Power

• Generator Unit Governors:• Governor droop control is generally not quick

enough to prevent major decreases in system frequency.

• All governors (on larger units which will contribute to spinning reserve) should be set at 4% droop.

• A software error discovered on the Low Speed governor control should be corrected to allow these units to operate in load control mode.


PB PowerPB Power

• Generator Unit Governors (Cont’d):• Set governor limits on the Low Speed units to the

engine overload setting. This will add approximately 2 MW (with all 4 engines in service) to the effective spinning reserve on the system at no additional cost.


PB PowerPB Power

• Generating Unit Size:• The proposed 30 MW Low Speed unit will not

compromise system reliability provided:

a. The existing load shed scheme modified for fewer larger blocks.

b. 10 MW spinning reserve operated for load demand levels <70 MW.

• The optimum spinning reserve of 10 MW (for demand<70 MW) after installation of the 30 MW unit is due primarily to the minimal impact this unit will have on despatch costs.


PB PowerPB Power

• Other Considerations:• Improve governor response on Steam Units.

(Woodward UG8 governors presently installed). Consider upgrading to electronic governing.

• Implement selective load shedding for “interruptible” customers.

• The issue of reliability should be addressed in the tender for any new plant, e.g. trips due to equipment failure or malfunction exceeding a certain amount, will result in a penalty being applied.


PB PowerPB Power


Thank YouThank You

Documents

PB Power. Determining Optimum Spinning Reserve 2001 CARILEC Engineers Conference July 25th - 27th, 2001 Roger Blackman Barbados Light & Power Pedro J