Page 55 - Handbook of Electrical Engineering

34 HANDBOOK OF ELECTRICAL ENGINEERING

The turbine energy changes from U tea to U tea + U tea . Substitute (2.40) into (2.29),

nt
U tea + U tea = C pt T 3 (1 − (r pt + r pt ) )η t
nt−1 nt
n n t P 3 n t r pt
= C pt T 3 η t 1 − r pt + P 223 − P 4
nt
P 4 P 4
from which,

nt−1 r pt P 4 − r pt P 1 − P 23
U tea =+n t η t C pt T 3 r pt (2.41)
P 4
The change in efficiency η pa in (2.33) is,

U tea + U tea − U cea − U cea
η pa + η pa = (2.42)
U fea + U fea
from which, by substituting for U tea , U cea = 0.0and U fea = 0.0 and deducting the initial con-
ditions gives,
U tea
η pa = (2.43)
U fea
The change in work done on the generator

U outea = U tea kJ/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 drops P 1 and P 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 Power Heat
of water output rate
Inlet 0.01245 5.0 −2.00 +0.75
Exhaust 0.006227 2.5 −0.50 +0.40