Handbook of Electrical Engineering

34 HANDBOOK OF ELECTRICAL ENGINEERING

The turbine energy changes fromUteatoUtea+Utea. Substitute (2.40) into (2.29),

Utea+Utea=CptT 3 ( 1 −(rpt+rpt)nt)ηt

=CptT 3 ηt

[

1 −

(

rptn+

ntP 3 nt−^1

P 4 nt

P 223 −

ntrptnt

P 4

P 4

)]

from which,

Utea=+ntηtCptT 3 rptnt−^1

[

rptP 4 −rptP 1 −P 23

P 4

]

( 2. 41 )

The change in efficiencyηpain (2.33) is,

ηpa+ηpa=

Utea+Utea−Ucea−Ucea

Ufea+Ufea

( 2. 42 )

from which, by substituting forUtea,Ucea= 0 .0andUfea= 0 .0 and deducting the initial con-
ditions gives,

ηpa=

Utea

Ufea

( 2. 43 )

The change in work done on the generator

Uoutea=UteakJ/kg ( 2. 44 )

Note that in the above analysis the signs of the practical changes are,

P 1 is negative

P 23 is negative

and P 4 is positive

The pressure dropsP 1 andP 4 are dependent upon the layout of the gas turbine generator,
the dimensions of the ducting systems and the specification of silencers and filters.P 23 is fixed by the
design of the combustion system and cannot be changed by external factors such as ducting systems.

2.2.4.1 Typical values of pressure drop losses

A newly installed gas turbine generator can be taken to have the typical losses given in Table 2.2.

Table 2.2. Typical pressure drop losses in gas turbine

Inlet or Pressure drop % change in

exhaust

Bar Inches

of water

Power

output

Heat

rate

Inlet 0.01245 5.0 −2.00 +0.75

Exhaust 0.006227 2.5 −0.50 +0.40