Electrical Power Systems

26 Electrical Power Systems
where y is the number of layers where in the single central strand is counted as the first
layer. The overall diameter (D) of a stranded conductor is
igure 2.5 shows the cross-sectional view of an
ACSR conductor with 24 strands of aluminium and 7
strands of steel.
Expanded ACSR conductors are used in extra high
voltage (EHV) transmission line. By the use of a filler
such as paper or hessian between various layers of
strands so as to increase the overall conductor diameter
to reduce the corona loss and electrical stress at
conductor surface. Bundled conductors are commonly
used in EHV transmission line to reduce the corona
loss and also reduce the radio interference with
communication circuits.
D = (2y – 1)d ...(2.48)
2.9 INDUCTANCE O COMPOSITE CONDUCTORS
In the previous sections, solid round conductors
were considered for the calculation of
inductance. However, stranded conductors are
used for practical transmission lines. igure 2.6
shows a single phase line comprising composite
conductors X and Y. The current in X is I
referenced into the page and the return current
in Y is –I. Conductor X having n identical strands
or subconductors, each with radius r x. Conductor
Y having m identical strands or subconductors
with radius r y. It is assumed that the current
is equally divided among the subconductors. Thus, each subconductor of X, carry a current I/n
and each subconductor of Y, carry a current –I/m.
Applying eqn. (2.46) to subconductor a, we get
l a = 0.4605 I
or l a = 0.4605 I log
R
S|
T|
RST
R
S|
T|
1 1 1 1 1
log log log log . . . log
n r¢ D D D D
+ + + + +
x
ab ac ad an
–0.4605 I 1 1 1 1
log + log + log + ... + log
m D D D D
The inductance of subconductor a is
aa¢ ab¢ ac¢ am
aa¢ ab¢ ac¢ am
1
m
1
x ab ac ad an
n
( D × D × D .... D )
( r¢ D D D .... D )
ig. 2.5: Cross-sectional view of
ACSR conductor (7 steel strands and
24 aluminium strands).
ig. 2.6: Single phase line consisting of
two composite conductors.
U
V|
W|
UVW
U
V|
W|
...(2.49)