PHM	Prognostic and health management
MCS	Modified Cuckoo Search Algorithm
BP	Back-propagation
MCS-BP	Modified Cuckoo Search Algorithm optimized Back-propagation neural network
DGA	Dissolved gas analysis
GA	Genetic algorithm
PCA	Principal component analysis
PSO	Particle Swarm Optimization
IR	improvement rate
$\alpha$	step-size
$P_a$	discovery probability
f	fitness function
$\lambda$	Lévy exponent
$P_c$	switching probability
$P_m$	mutation probability
$a^l$	activation functions
C	cost function
${\sigma }^L$	output error
MVO	multi-verse optimizer
MLP	multi-layer perceptron
PNN	probability neural network
MSE	mean square error
SVM	support vector machine
$x_i^t$	the nest in t generation
$x_i^{t+1}$	the nest in t + 1 generation