Review of accumulative failure of winding insulation subjected to repetitive impulse voltages

Abstract

The premature failure phenomenon that occurs in solid insulation under the application of repetitive impulse voltages is known as the accumulative effect of impulse voltages on a solid dielectric. The accumulative failure of winding insulation is considered to be a core problem resulting from this phenomenon. The main problems include the accumulative failure of motor winding insulation under pulse-width modulation impulses and the accumulative failure of transformer winding insulation under the application of overvoltages, and these problems represent new challenges in the safe and stable operation of power grids. With regards to the above problems, this study reviews the results of recent research on the accumulative failure characteristics and mechanisms of winding insulation when subjected to repetitive impulse voltages. The challenges faced are discussed at the end of this study.

Method of inter‐turn fault detection for next‐generation smart transformers based on deep learning algorithm

“…N is the total number of training vector x i ; n is the dimension of each input vector; m is the size of hidden nodes. In (1), function f() is called the activation function. Typically, it is sigmoid function which is defined as…”

“…Thus, the input vector will be divided into the category with the high probabilities. Given a group of labelled input vector {x (1) , x (2) ,…, x (k) }, x i ∈ R n and y i being the corresponding label, the probability that x i belongs to a certain class j, j = 1, 2, …, q can be calculated as follows [20]:…”

Impulse Breakdown Characteristics of Transformer Oil with Cellulose Particles in Quasi-Uniform Field

“…Transformer oil plays a major role in insulation and heat dissipation, and is the main insulating medium inside oil-immersed transformers. The dielectric strength of transformer oil has attracted much attention [1][2][3]. Oil-paper insulation is the main insulation system of the oilimmersed transformer.…”

Accumulative effect of partial discharges at impulse voltage wave tail

“…Today, the ubiquitous application of power electronics means that the electrical insulation of power equipment is exposed to various continuous impulse stresses. Example applications include high-voltage direct current (HVDC) systems, converter fed transformers, pulse-width modulation (PWM) driven motors which allow for fluctuation of the average value of the waveform or smart grids where the voltage levels of the system may be reconfigured to various voltage levels [8][9][10][11][12][13][14]. Electromobility brings a new class of challenges, where higher and higher voltage level will be involved in the power train of electric vehicle.…”

“…The second aspect refers to the above-mentioned impulse stresses generated on insulation systems resulting in PD activity. Special attention should be paid to the danger of the accumulative effect of repetitive impulse voltages on insulation [14,15]. Formerly focus was on the voltage distortion caused by harmonics [16], while over the last decade the influence of steep waveforms launched by converters with fast semiconductors like insulated gate bipolar transistor and recently wide-bandgap (SiC, GaN) devices is considered as even more dangerous [17][18][19][20][21][22][23].…”