Handbook of Electrical Engineering

GAS TURBINE DRIVEN GENERATORS 57

Figure 2.18 Simulation of slewing of the fuel valve by using an exponential approximation.

integrating betweent 1 =0andt 2 =Te, whilst area (B) is found by integrating betweent 1 =Teand
t 2 =T 100. If R is the slewing rate in per unit movement per second, then the solution for the best
measure of fit is,
1
2 R

=( 1 −e−f)Tfaseconds

Where,

f=

− 1

RTfa

Hence a unique value ofTfacan be found for each value of slewing rateR. The ratio of
1.0/TfatoRthat satisfies the above equation for all non-zeroRis,

1

RTfa

= 1. 5932 ,which may be rounded up to 1.6

If for example the slewing rate is 3 per-unit travel/second then 1. 0 /R= 0 .333 andTfa=
0. 333 / 1. 6 = 0 .208 seconds.

If this approximation is made then an additional lag term should be inserted in the denominator
of the ‘fuel valve lag’ block described in sub section 2.6.1.7 and the hard limits simply applied to
the output of the block.