Primary Frequency Control
Free Governor Mode of Operation
Boiler-Turbine-Generator System
Units with different Ratings and Same
Governor Droop of 3%
Frequency in Hz
Governor Regulation
52.5
52
51.5
51
50.5
50
49.5
49
48.5
48
47.5
U1:200MW3%
U2:400MW 3%
U3:200MW 3%
U4:400MW 3%
0
100
200
300
Unit Loading in MW
400
500
Governor Regulation with different ratings
and different droop constants
Frequency in Hz
Governor Regulation
50.5
50
49.5
49
48.5
48
47.5
47
46.5
U1:200MW 3%
U2:200MW 6%
U3:400MW 3%
U4:400MW 6%
0
100
200
300
Unit Loading in MW
400
500
Two Units : Same Rating, same droop
Two Units : Different Ratings, Same droop
Two Units : Same Rating, Different Droops
Three Units : One unit Regulating
Three Units: Two Units Regulating
Two machines of capacity 200MW with 6% Governor droop and 500MW with 3% Governor
droop are operating in parallel with 150MW and 300MW loads to meet a total demand of 450MW
at 50Hz in an isolated system. If the total load increases by 100MW to 550MW, what is the
resultant load shared by each unit and the resultant frequency of the system.
The increase in load of a unit with P1 MW
Rating and R1%droop is
P1  (P1 / R1 )

P1 = K (P1 / R1 )
Similarly P2  (P2 / R 2 ) ,
 P2 = K (P2 / R 2 )
Total load change = P1 + P2 = 100MW
P = 100 MW = P1 + P2
=
 P1
K

 R1
=100MW =
P2 
R 2 
 200
K

 6
500
3 
Example contd.
 200 1000
100 MW  K 

6

K
1200
6
K
P1  K
P2  K
 K (200 )  100
100
200

P1
1

R1
2
F 2 
1
2
200
6
X

200
12

50
3
 16.66
 P2 

 
 R2 
1
2
X
50
3

250
3

50

3
1
200
 3  0.25 Hz
1
500
 1.5  0.25 Hz
P  P1  P 2 
F1 

P1
 F1 
P1
P 2
 F2
P2
250
3

500

3
300
3
250
 83.33
3
 100
FGMO in Integrated Systems: Two Units Shifting Load by changing the Reference
System
FGMO in Integrated System: Droop
Characteristic showing Load Limit Less than
Full Load
Governor Action in an Integrated System
Governor Response to Sudden Loss of
Generation
Governor Response:
Boiler-Turbine-Generator System
Temporary Increase in Droop Due to Boiler
Effects
Response Characteristics for Boiler-TurbineGenerator Control Systems
Bibliography
1. Cohn, N.. Control of Generation and Power Flow on
Interconnected Systems, WHey, New York, 1961.
2. Miller, II.. Power System Operation. McGraw-Hill, New
York1970.
3. Weedy, B., Electric Power Systems, Wiley, New York.
1967.
4. Woodward Governor Co., “Role of Governors in System
Operated Unified Control of Hydro Units, Prime Mover
Control”