Page 163 - Practical Power System and Protective Relays Commissioning

Chapter 16

Power System Fault Analysis

16.1 BASIC SYSTEM RELATIONSHIPS

S 5 total power 5 O3 V L I L
P 5 real power 5 O3 V L I L cos (Φ)
Q 5 reactive power 5 O3 V L I L sin (Φ)
V L 5 line voltage, V L 5 O3 V PH , V PH 5 phase voltage, cos (Φ) 5 power
factor as shown in Fig. 16.1 which describes the relation between the
power system quantities in vector diagram representaion.
Operator a:
2
2

a 5 1+120 ; a 5 1+240 ; 1 1 a 1 a 5 0
Operator J:
2

j 5 1+90 ; j 52 1
MVA base 5 O3 kV base 3 I base . The common usage is 100 MVA as base
MVA
MVA b
Z% 5 ZðΩÞ 3
ð KvÞ 2
Z% 5 MVA b 3 100, where MVA F 5 fault MVA
MVA f

16.2 SYMMETRICAL AND UNSYMMETRICAL COMPONENTS
Any unsymmetrical phasors can be analyzed as three symmetrical compo-
nents, as shown in Fig. 16.2.

16.2.1 Positive Sequence

The three phasors are equal in magnitude. They are displaced from each
other by 120 degrees in phase, and have the same phase sequence as the
original phasors.

Practical Power System and Protective Relays Commissioning.
DOI: https://doi.org/10.1016/B978-0-12-816858-5.00016-2 163
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