06 power plant frequency response
DESCRIPTION
Stability studyTRANSCRIPT
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Power Plant Frequency Response
John UndrillSeptember 2006
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FRR is a Balancing Authority Obligatio
But - the response must be produced by the turbines inthe Balancing Authority Area
Because frequency changes rapidly, a major part of the complete response must be produced in a 10-20 second time frame
Therefore - a major part of FRR must be primary response
The Primary Controller is the Governor
Primary Response is Governor Response
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Production of Frequency Response
Frequency Response is produced inherently by governor action
If unit is not at maximum governor should respond
But governor action may be blocked, overridden or countermandedPlant physics may require that limits be placed on primary response
eg. temperature - hydraulics - drum level control
Commercial considerations may inducd limits on primary responseeg. valve wear - compensation for foregone revenue
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Primary and Secondary Control
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Primary - Secondary Control
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Primary Control = Governing
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Primary - Response
Governor Responds to speed change
Speed dips when load increases
Power increases to equal increased load
No change in speed/load reference
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y p
Primary Response | Secondary Response - AGC adjusts speed-load references
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gGrid Frequency
Fuel Command
Generator PowerGovernor
Responds to Frequency
changePlant ControllerReturns Power
to Schedule
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gGovernor Responds to Frequency
change
Plant ControllerReturns Power
to Schedule
Primary Control
Secondary Control
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gPrimary and Secondary Response
Primary Response Test -
No secondary Control Action
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Hydro Plant Characteristics
o - Control action involves large pieces of equipment
- Temperature is not a factor
- Principal limitations are in hydraulics of civil works
- Rough running/draft tube stability my limit allowabledispatch ranges - but have little effect on primaryresponse capability
- Surge tank/manifold design may affect primary respo
- River hydrology often affects allowable secondary response
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Steam Plant Characteristicser - Boiler control must respect dozens of rate limits
mperature stresses, drum level, coal mills, feedwater heating
al - Boiler Follow - Older plants- Primary response is steam turbine response- Steam turbine response can be very fast - 5% in 5 seconds- Useable Primary response is limited by boiler response capability- Plant capability - 5% fast - remainder - 2%/min or less
al - Turbine Follow - Supercritical and older very large plants- Primary response is boiler response- Turbine valves are used to control steam pressure - not power- Primary response to frequency is very limited and slow- Secondary response is limited by boiler response capability- Plant capability - 0% fast - remainder - 2%/min or less
al - Coordinated Control - Modern / Updated plants- Primary response is steam turbine response- Feedforward of steam demand signal to firing control
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Main Plant Characteristics
- Primary response of gas turbine is fast- Generally better going up than coming down- Frequently desirable to implement rate limits to managetemperature transients
- Plant capability - 10 to 15 percent fast - remainder - 8%/mi
GT - Primary control (governor) acts on GT- ST valves are wide open in economical output range- ST output follows GTs - behind boiler response time consta- GT component of response is fast- ST component of response is slower- Plant capability - 5 to 8 percent fast - remainder - 3 to 5%/m
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Gas Turbine Plants
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100 sec
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Hydro Plants
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p y p
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Large Steam Plants
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g y y p
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Summary of FRR Capability
ge Modern Coal5 % in few seconds 1-3 % per minute
ce Thru & Turbine follow Coal0 % in few seconds 1-3 % per minute
er Boiler Follow Coal5 % in few seconds 1-3 % per minute
ro5-10 % in 15 seconds fast over full range
10-15 % in 15 seconds 8 % minute
GT5 - 8 % in 15 seconds 5-8 % minute
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Summary of Operational Realitiesal
ideal capability overidden byturbine temperature/stress limitsdrum level controlfeedwater heater level controlscoal feeder/mill limitations
rolow head - few limitationshigh head/underground/pipeline - civil works limitations
concern regardingreduced output economicswear of valveshot gas path exposure due to maneuvering
GTGT as in cimple cycle plantsST stress and boiler feedwater limitations as in coal plants