Per unit system values - Modelling Distributed Energy Resources in Energy Service Networks - page 183

Appendix F
Per unit system values

In order to facilitate the load flow calculations in this work, a per unit system
was employed. In electrical engineering, this methodology is widely used and this
realm is expanded here to cover natural gas networks as well. Per unit values are
expressions of system variables as fractions of a defined base unit quantity. These
calculations are simplified and easy to read because quantities expressed in this man-
ner are the same regardless of the voltage or pressure levels. Therefore, conversion
of per unit quantities requires a knowledge of the base value that the quantities have
as Reference 245.

F.1 For electrical networks ( i.e. single phase)

Assuming the independent base values are apparent power and voltage, we have:

S base = 1pu (F.1)

V base = 1pu (F.2)

As a consequence, the values for the rest of the variables can be derived:

S base
V base =

=

I base 1pu (F.3)

V base
I base =

V base V base

Z base =

I base V base = S base =

1pu (F.4)

1
Z base =

Y base = 1pu (F.5)

F.2 For natural gas networks

Assuming the independent base values are power and pressure, we have:

=

G base 1pu (F.6)

p base = 1pu (F.7)