Isolation transformer

About: Isolation transformer is a research topic. Over the lifetime, 8145 publications have been published within this topic receiving 72396 citations.

Insulating IGBT driver with PCB integrated capacitive coupling elements

Abstract: In many power electronic applications galvanic isolating IGBT/MOSFET drivers are advantageously used. The main reasons are safety issues, driving high voltage power semiconductors with blocking voltages of typically 600 V or above and avoiding or minimizing unwanted ground current loops. This paper deals with a new method for achieving galvanic isolation in high voltage drivers based on printed circuit board (PCB) integrated capacitive coupling elements. The suggested coupling element consists of a pair of plate capacitors by using copper layers and prepregs of a PCB. First, the influence of the isolation barrier capacitance, which is one of the main important parameters of a galvanic insulating driver, is illustrated by a simple model of the capacitive current loop. As a result it is stated that the coupling capacitance should be lower than 5 pF to achieve high dV/dt levels of at least 100 kV/μs. Taking into account the isolation characteristics of the commonly used FR4 PCB material, an integrated capacitive coupling element can be designed. With 360 μm isolation distance and a plate surface of approximately 8 mm², a capacitance of about 1 pF is achieved. A comparison of the developed capacitive coupling element with a comparable inductive coupling element (transformer) shows that the former has advantages due to a much lower current consumption and less dependency on parasitic inductances. In order to achieve high isolation voltages on PCBs, wide creepage and clearance distances are required, especially at higher humidity levels. It is advisable to use special layout were the primary and the secondary circuits of the driver are placed on different sides on the PCB by using blind vias. The well known Manchester coding can be applied to use the advantages of phase modulated signals for transmitting the switching signal over the isolation barrier. By transmitting the carrier signal via a second capacitive coupling element, the complexity for decoding the switching signal is reduced. A half bridge driver was built up to verify the new isolation method. Herewith a bidirectional buck-boost DC/DC converter operating at a DC link voltage of 400 V was successfully controlled. Moreover, measurements with a standardized burst generator have shown, that a fail-safe operation is possible up to high dV/dt levels.

On-line monitoring of winding deformation of power transformer

Abstract: The feasibility of estimating transformer winding deformation by measuring short-circuit reactance is expounded. Based on the theoretical research, the on-line measurement system for short-circuit reactance of a transformer is proposed. The study on a power transformer in actual operating condition shows that the on-line method is satisfactory for detecting short-circuit reactance variations with high degree of accuracy and good stability, and can be used for detecting deformation in the transformer windings.

Comparison of Impulse Wave and Sweep Frequency Response Analysis Methods for Diagnosis of Transformer Winding Faults

Abstract: Monitoring of winding faults is the most important item used to determine the maintenance status of a transformer. Commonly used methods for winding-fault diagnosis require the transformer to exit operation before testing and an external exciting signal, whether the transformer is malfunctioning or not. However, if an overvoltage signal can be regarded as a broadband excitation source for fault diagnosis, then the interference caused by signal injection can be eliminated without the need for additional pulse or impulse signals. In this paper, a tapped transformer is designed and test platforms are built to compare winding diagnoses using the impulse wave and sweep frequency response analysis methods by recording voltage responses on both the high- and low-voltage sides and calculating the respective transfer functions. Based on comparison of statistical indicators, it is found that the sensitivities of both methods are similar for detecting conditions of winding-ground and winding-interlayer short circuits. It is concluded that it is feasible to use a transient overvoltage monitoring system for winding-fault diagnosis.

A power transformer as a source of noise.

Abstract: This article presents selected results of analyses and simulations carried out as part of research performed at the Central Institute of Labor Protection – the National Research Institute (CIOP-PIB) in connection with the development of a system for active reduction of noise emitted by high power electricity transformers. This analysis covers the transformer as a source of noise as well as a mathematical description of the phenomenon of radiation of vibroacoustic energy through a transformer enclosure modeled as a vibrating rectangular plate. Also described is an acoustic model of the transformer in the form of an array of loudspeakers.

Output Characteristics of a Kind of High-Voltage Pulse Transformer With Closed Magnetic Core

Abstract: A new kind of miniature high-voltage pulse transformer based on closed magnetic core is developed, and its output characteristics are analyzed in this paper. The amplitude of the output high-voltage pulse of the transformer is 210 kV, the step-up ratio is 1:105, and the effective coupling coefficient is 0.984. The time-domain and frequency responses of the transformer have also been analyzed in detail by circuit theory. The experimental results show that the pulse transformer can respond well to square voltage pulse with a pulsewidth ranging from 5 to 100 ?s and a frequency band ranging from 100 Hz to 500 kHz. With these characteristics, the small pulse transformer with very low cost can be used for applications of dielectric barrier discharge and high-voltage nanosecond-pulse generator.