Page 71 - Handbook of Electrical Engineering

50 HANDBOOK OF ELECTRICAL ENGINEERING

Similarly for generators Nos. 2 and 3,

f z2 = 61.411 Hz and f z3 = 61.951 Hz

Step 7. Find the new set points that will recover the frequency to 60 Hz whilst maintaining equally
loaded generators.
Let the desired frequency of 60 Hz be denoted at f d . In order to reach this frequency all the
set points need to be increased by the difference between f d and f ,which is,

f = f d − f = 60.0 − 59.25101 = 0.749 Hz

Therefore,

f z1 = 60.871 + 0.749 = 61.62 Hz
f z2 = 61.411 + 0.749 = 62.16 Hz

and
f z3 = 61.951 + 0.749 = 62.70 Hz

Check that f has now the correct value, by using (2.62),

D 1 P 1 f o 0.03 × 18.0 × 60
f = f z1 − = 61.62 −
G 1 20
= 61.62 − 1.62 = 60.0Hz
0.04 × 13.5 × 60
D 2 P 2 f o
f = f z2 − = 62.16 −
G 2 15
= 62.16 − 2.16 = 60.0Hz
and,
D 3 P 3 f o 0.05 × 9.0 × 60
f = f z3 − = 62.70 −
G 3 10
= 62.70 − 2.70 = 60.0Hz

2.5.5 Load Sharing Controllers

The above worked example illustrates the combination of droop governing with an overall isochronous
control function. In a practical control scheme the following variables can be easily measured by
suitable transducers,

f = the system frequency.
P i = the electrical power at the terminals of the generator (the generator losses and
gearbox losses can be ignored).
f zi = the governor set point within the controller that drives the fuel valve. A suitable
potentiometer can be used to derive the signal.