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Turbine Governor Frequency Coordination

Frequency coordination keeps the unit load demand to the boiler in line with any actions takenby the turbine speed governor. During a frequency upset on the power grid, the turbine speed

governor provides direct and prompt proportional control action on the turbine to correct the

frequency upset. Frequency coordination indexes the unit load demand to match the loadconditions being required by turbine speed governor to prevent incorrect interactions between the

boiler control system and the turbine speed governor while a frequency error exists.

The frequency correction logic is proportional only control with a deadband which must have the

same proportional gain and deadband settings (droop) as the turbine speed governor. A typical

curve is shown in Figure ULD-2. When either the boiler or turbine is on manual control or a unit

runback is in progress, unit load demand frequency coordination must be disabled.

Governor Droop - the decrease in frequency to which a governor responds by causing a

generator to go from no load to full load. This definition of governor response is more precisely

defined as "speed regulation," which is expressed as a percentage of normal system frequency.For instance, if frequency decays from 60 to 57 hertz, a 5% change, a hydro generator at zero

load with a governor set at a 5% droop would respond by going to full load. For smaller changes

in frequency, changes in generator output are proportional. The more technically correctdefinition of governor droop is the change in frequency to which a governor responds by causing

the turbine gate position to move through its full range of travel, which is generally non-linear

and a function of load.

Governor Dead Band - A range of control signal input to the governor in which there is neitheran increase nor decrease in the governor output.

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NERC Operating Manual

1. Governor installation. Generating units with nameplate ratings of 10 MW or greater should beequipped with governors operational for frequency response unless restricted by regulatory

mandates

2. Governors free to respond. Turbine governors and HVDC controls, where applicable, should be

allowed to respond to system frequency deviation, unless there is a temporary operating problem.

3. Governor droop. All turbine generators equipped with governors should be capable of providing

immediate and sustained response to abnormal frequency excursions. Governors should provide a

5% droop characteristic. Governors should, as a minimum, be fully responsive to frequency deviations

exceeding 0.036 Hz ( 36 mHZ).

4. Governor limits. Turbine control systems that provide adjustable limits to governor valve movement

(valve position limit or equivalent) should not restrict travel more than necessary to coordinate boiler and

turbine response characteristics

Graph showing relation between generator output and Interconnection frequency at 0, 50%, and 100%LOAD for a 5% governor droop characteristic.

5% Governor Droop

57

58

59

60

61

62

63

0 20 40 60 80 100

Percent Outpu

Freque

ncy

-Hz

Full Load

50% Load

No Load