Static Voltage Stability Analysis Based on PSS/E - Intelligent Computing for Sustainable Energy and Environment - page 195

limit and the corresponding running voltage. While the voltage instability or
voltage collapse is a dynamic phenomenon under large or small disturbance,
easily influenced by load restore characteristic and generator system, the maxi-
mum power transfer point is not necessarily the voltage instability point[3].
The Siemens PTI Power System Simulator (PSS/E) is a package of programs
for studies of power system transmission network and generation performance in
both steady-state and dynamic conditions. Many scholars have researched and
explored the software application in depth [4,5] .

2Mod lD ip on

A. Contingency Ranking
In large systems with many possible contingencies, especially single branch out-
ages, it is often useful to minimize the computational and subsequent analyses
by identifying the most severe contingencies prior to performing the contingency
analysis. The method of contingency ranking has been discussed and studied in
many references[6-8].This paper uses voltage depression criteria to rank branch
contingencies.
In the voltage ranker, the performance index is defined as:

L

X i P i PI = (1)

i =1

where:
X i - is the reactance of branch i .
P i - is the active power flow on branch i .
L - is the set of monitored branches contributing to PI .
PI gives an indication of reactive power losses under different system condi-
tions. As line loadings increase, their I 2 X losses also increase. This increase in
reactive demand generally results in a depression of system voltages.

B. PV Curve
PV curves are parametric study involving a series of ac power flows that moni-
tor the changes in one set of power flow variables with respect to another in a
systematic fashion. This approach is a powerful method for determining transfer
limits that account for voltage and reactive flow effects. As power transfer is
increased, voltage decreases at some buses on or near the transfer path. The
transfer capacity where voltage reaches the low voltage criterion is the low volt-
age transfer limit. Transfer capacity can continue to increase until the solution
identifies a condition of voltage collapse; this is the voltage collapse transfer
limit. It can be explained as Fig.1.

E s
Z LN

cos φ

P R = V R I cos φ = Z LD
F

(2)

1
√ F

Z LD
Z LN E s

V R = (3)