$a_j^l$	the output value	SSA	Sparrow Search Algorithm
$b_j^l$	the bias	ISSA	Improved Sparrow Search Algorithm
d	the distance	DGA	Dissolved Gas Analysis
down(.)	the pooling function	ELM	Extreme Learning Machines
fi	the fitness value	ANN	Artificial Neural Networks
K	the step size coefficient	SVM	Support Vector Machines
M	the window length	ES	Expert Systems
Mjl	the selected set of input feature maps	ApEn	Approximate Entropy
N	size of the input data	MApEn	Multi-scale Approximate Entropy
R	the threshold	PSO	Particle Swarm Optimization
$t$	the iterations	GWO	Grey Wolf Optimizer
Τ	the time scale	GSA	Gravitational Search Algorithm
$u(i)$	he original signal	AVOA	African Vultures Optimization Algorithm
$X_{gauss}^t$	the Gaussian best solution	ReLU	Rectified Linear Unit
X	the original data matrix	NT	Normal type
x(i)	vectors with a dimension of m	HD	High-energy discharge
${\mathrm{y}}_j^{(\tau )}$	the coarse-grained process	LD	Low-energy discharge
$Z_I^K$	chaotic sequences	HO	High-temperature overheating
β j l	the multiplicative residua	ITO	Intermediate-temperature overheating
β	step size control parameter	ILO	Intermediate to low-temperature overheating
${\omega }_m$	non-linearly decreasing weight	PD	Partial discharge
BPNN	Backpropagation Neural Network