ABSTRACT
Let Iamp the actual current in ampere, Ib the base current in ampere, Vvolt the actual voltage in volts, Vb the base voltage in volts, Zohm the actual impedance in ohms, Zb the base impedance in ohms, Svolt-amp the actual volt-ampere, and Sb the base volt-ampere, then
Per-unit current pu
b = =I
I I
(2.3)
Per-unit voltage pu volt
b = =V VV
(2.4)
Per-unit impedance pu ohm
b = =Z ZZ
(2.5)
Z R jX
Z ZZ R Z j
X Z
= +
∴ = = +
or
Z R jXpu pu pu= +
∴ =R RZpu
b (2.6)
and
X XZpu
b =
(2.7)
Per-unit volt-ampere
S
S Spu
b =
(2.8)
S P jQ VI
S S
S P S j
Q S
S P jQ
= + =
= = +
∴ = +
∴ =P PSpu
b (2.9)
∴ =Q QSpu
b (2.10)
For a single-phase circuit,
Z VIb
b =
(2.11)
and
S V Ib b b= (2.12)
e values of the base quantities are selected according to convenience. If any two of the four quantities in Equations 2.11 and 2.12 are specied, the remaining two are xed automatically.
