Autotransformer Winding Research Articles

Defect Diagnosis for Autotransformer Winding in High-Speed Railway Based on Transfer Function Pole Distribution

Defect Diagnosis for Autotransformer Winding in High-Speed Railway Based on Transfer Function Pole Distribution

Non‐isolated resonant quasi‐Z‐source network DC–DC converter

A novel non-isolated resonant quasi-impedance (quasi-Z)-source network DC–DC converter is proposed. The resonant impedance source network is derived from the quasi-Z-source network by including the autotransformer-based resonant cell instead of the second inductor of the quasi-Z-network. The leakage inductance of the autotransformer and two resonant capacitors connected in series with the autotransformer windings constitute a high-frequency resonant tank. At the same time, the resonant capacitors block the DC-bias current of the autotransformer. The resonant operation with a sinusoidal current of the main switch and diodes enables electromagnetic interference mitigation and improves the efficiency of the converter. Experimental results of a 100 W, 30 V/200 V prototype are presented to verify the analysis results of the proposed converter.

Actual Measurement and Analysis of DC Magnetic Bias of 750kv Autotransformer

Monopole to ground operation mode of ultra high-voltage DC transmission system will result in DC magnetic biasing phenomenon to transformers in surrounding AC substation. Under monopole to ground operation mode of ±800kV “Qi-Shao” ultra high-voltage DC transmission project, DC magnetic biasing hazard of transformers in AC power network in sending terminal—Jiuquan region was tested. It’s found that after capacitive DC blocking device of 750kV transformer neutral point was put into action, transformer vibration and noise still gradually increased with ground current at ground electrode, so ideal governance effect was not reached. Regional DC current distribution after series capacitance at transformer neutral point in 750kV Dunhuang substation was analyzed in this paper. It’s found that DC current could still flow through autotransformer winding so as to make the transformer be still influenced by DC magnetic bias. Meanwhile, based on analysis of secondary-side waveforms at neutral point of 750kV autotransformer, it’s found that transformer magnetizing current went through serious distortion with current increase at ground electrode after action of DC blocking device. Harmonic analysis was conducted for distorted waveforms and change features of secondary harmonics were used, which provided a convenient and effective means of monitoring DC magnetic biasing hazard of 750kV autotransformer.

Mathematical model of high-voltage instrument autotransformer intended for use in smart grid networks

The object of the research is a mathematical model of the active part of the high-voltage instrument autotransformer with several output windings. The most challenging task in this model is leakage inductance calculation of single winding turns or groups of autotransformer winding turns. Also, a significant problem when calculating the parameters of the autotransformer are those operating conditions, that are close to no-load conditions. To create a mathematical model of the active part of a high-voltage autotransformer, taking into account the leakage inductance of each single winding turn (or groups of winding turns), and also the magnitude and type of the load, it is proposed to modify the known system of transformer equations detailed to the level of single turns (or groups of turns) and use the proposed method for determining the partial self- and mutual- leakage inductances by numerical methods. With a help of the developed mathematical model of the active part of a high-voltage autotransformer, a prototype of a 10 kV autotransformer with high metrological characteristics was designed and manufactured. Positive results of metrological certification of the created high-voltage autotransformer confirmed the possibility of calculating the parameters of such primary high-voltage transformers that can be used in Smart Grid networks in conjunction with analog-to-digital converters, thus unifying the electromagnetic primary high-voltage transformers. It is shown that the operating conditions of high-voltage autotransformers, close to no-load conditions, allow easily achieve high accuracy of high voltage transformation.

Effects of pantograph arcing on railway systems with auto transformers

Conducted and radiated electromagnetic interferences on auto transformer (AT) caused by pantograph arcing in electrified railway system are investigated. The overhead lines of electrified railway system can be simplified by three parallel overhead conductor lines. The model of AT in this paper is situated at the end of lines. The propagation of electromagnetic waves along the three conductors is solved by using finite-difference time-domain (FDTD) method. The circuit model for AT is created by state variable equations, and the equations are discretized by backward Euler method. The pantograph arcing is represented by a trapezoidal voltage pulse which has a wide band of frequency just like an arcing has; the rise and fall time are determined by the main frequency. The voltages across the AT windings are computed by the final FDTD iterative equations when all factors are considered.

A nonintrusive auto-transformer technique for the measurement of void fraction

Winding low resistance wires around the tube of the test section in a method analogous to the auto-transformer winding was proved experimentally successful for the measurement of void fraction in the two-phase medium inside the tube. This novel technique is based upon the fact that the two-phase mixture becomes the region for a magnetic field where any change in the void fraction produces a change in the permeability of the two-phase mixture. The present technique is suitable for two-phase flows, which are contained in nonmetallic tubes.

Frequency response equalizing network for an electrostatic loudspeaker

An electrostatic loudspeaker system includes a transformer whose secondary winding is connected to the conductive plates of an electrostatic loudspeaker and whose primary winding is energized by an audio input signal through a frequency response equalizing network which includes an autotransformer winding as well as resistive and capacitive elements. Specifically, the autotransformer winding is connected in parallel with the primary winding, one audio input terminal is directly connected to one end of the autotransformer winding, at least one tap of the autotransformer winding is connected through a resistive element to the other audio input terminal and the other end of the autotransformer winding is connected to the other audio input terminal through a capacitive element.

Industrial x-ray equipment

Winding low resistance wires around the tube of the test section in a method analogous to the auto-transformer winding was proved experimentally successful for the measurement of void fraction in the two-phase medium inside the tube. This novel technique is based upon the fact that the two-phase mixture becomes the region for a magnetic field where any change in the void fraction produces a change in the permeability of the two-phase mixture. The present technique is suitable for two-phase flows, which are contained in nonmetallic tubes.