Power Plant Frequency Response

John UndrillSeptember 2006

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

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

Primary and Secondary Control

Primary - Secondary Control

Primary Control = Governing

Primary - Response

Governor Responds to speed change

Speed dips when load increases

Power increases to equal increased load

No change in speed/load reference

y p

Primary Response | Secondary Response - AGC adjusts speed-load references

g

Grid Frequency

Fuel Command

Generator PowerGovernor

Responds to Frequency

changePlant ControllerReturns Power

to Schedule

g

Governor Responds to Frequency

change

Plant ControllerReturns Power

to Schedule

Primary Control

Secondary Control

g

Primary and Secondary Response

Primary Response Test -

No secondary Control Action

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

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

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

Gas Turbine Plants

100 sec

Hydro Plants

p y p

Large Steam Plants

g y y p

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

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