FA
Firefly Algorithm
NB
Total number of buses
LIA
Load Incremental Algorithm
No
Total number of buses excluding slack buses
DE
Differential Evolution
NG
Number of PV buses
DEPSO
 Differential Evolution Particle swarm optimization
NPQ
Number of PQ buses
PSO
Particle swarm optimization
θij
voltage angle difference between buses i and j in radians
NP
Non-linear Programming
Bij
Transfer susceptance between buses i and j in p.u
PGi
Real Power generation at ith bus
Gij
Transfer conductance between buses i and j in p.u
QGi
Reactive power generation at ith bus

Minimum power output in MW of unit j
QDi
Reactive power demand at ith bus

Maximum power output in MW of unit j
PDi
Real power demand at ith bus
Vimin
 Minimum voltage at ith bus in p.u

Increment load at bus i in addition to base load
Vimax
Maximum voltage at ith bus in p.u.
Itmax
Maximum number of iterations
Vi
Voltage at ith bus in p.u.
n
Total number of fireflies i.e. size of population
Is
Light intensity of a firefly at the source
 
 
Minimum value of incremental load for uth load bus of firefly f
γ
Light absorption coefficient of a firefly

Maximum value of incremental load for uth load bus of firefly f
rfh
Cartesian distance between two fireflies f and h
xf,k
kth component of the spatial coordinate xf of fth firefly
β
Attractiveness of a firefly with respect to other fireflies
xh,k
kth component of the spatial coordinate xh of hth firefly
I0
Original light intensity.
APSO
Adaptive PSO
Nc 
 
Number of buses violating minimum voltage constraint.
CPSO
Chaotic PSO
δ
A small step of incremental load