Isolation transformer

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

FRA vs. short circuit impedance measurement in detection of mechanical defects within large power transformer

Abstract: Power transformers are supposed to be and remain in service in various environmental circumstances under different electrical and mechanical stresses. Base on failure history in power transformers obtained from four corners of the globe one of the major problems in transformers is mechanical defect. A number of monitoring and diagnostic methods have been introduced to recognize transformer active part displacement and winding deformation. Frequency response analyses and short circuit impedance measurement have been employed as two common diagnosis methods in large power transformer winding deformation recognition. On the other hand, researchers are expressing an increased concern about power transformer condition monitoring in the smart grid context. Hence, all of off-line methods need to move towards on-line applications. One of the challenges is finding reasonably accurate method which can provide sufficient information about transformer winding condition. In this study, mechanical defects of windings and their causes are investigated in detail. Frequency response analyses and short circuit impedance measurement as two popular methods in transformer winding deformation diagnosis will be employed to get insight into transformer active part condition. A large power transformer has been taken as a case in order to put the capability and sensitivity of abovementioned methods into test. Onsite test results on this giant transformer winding show that frequency response analyses method is capable to provide far more information as to the healthy or defected condition and physical movements of the transformer's windings and core compared to the other method.

Effects of current and voltage harmonics on distribution transformer losses

Abstract: The drive to improve energy efficiency and reduce electrical loading has resulted in energy efficient lighting such as compact fluorescent lamps (CFLs) replacing conventional incandescent lamps However, the presence of such non-linear loads has brought about the injection of voltage and current harmonics into electrical networks As transformers are the interface between the supply and the non-linear loads, the investigation of their effects on transformer losses is of great importance These harmonics can cause excessive loss and abnormal temperature rise in the transformers, thus reducing their operational life span This paper investigates the impact of current and voltage harmonics of the loads on a single-phase 25kVA distribution transformer Harmonic spectra of a range of non-linear loads including CFL, LED tube, PC and fluorescent lamp are obtained A single-phase inverter is used for harmonic generation to simulate power supply harmonics injected into the transformer Open circuit and short circuit tests are conducted on the transformer under the effect of harmonics, and the impacts on core loss are analyzed

Power transformer monitoring using UHF sensors: installation and testing

Abstract: External UHF couplers have been fitted to a 1000 MVA autotransformer as part of a project aimed at developing new transformer monitoring techniques. The couplers will supply valuable raw data from a transformer operating under normal service conditions. UHF signals were recorded while the transformer was re-energized and returned to load. Initially, some large discharges appeared, but these were short-lived. Background signal levels were low, indicating no significant interference problems. A small intermittent discharge signal was recorded and its characteristics are described. The possibilities for UHF monitoring of transformers are discussed, together with some of the remaining challenges.

An accurate method for modeling transformer winding capacitances

Abstract: A simple method of modeling parasitic transformer capacitances is presented. This method allows determination of quantitative values for various transformer parasitic capacitances, allows the utilization of a transformer model for circuit analysis that takes the parasitic effects into account, provides a means of critically judging the merits of various winding configurations, and allows the designer to determine whether a given circuit configuration will increase or minimize the effect of transformer parasitic capacity. Voltage and energy relationships are described for uniform field discrete capacitors. Terms that provide a precise way of characterizing these relationships are defined, and examples are given. Nonuniform field capacitive energy storage as found in layer-wound or toroid structures is investigated. With these relationships established, the modeling methodology is presented by a series of examples. It is shown that what appear to be small changes in circuit configuration can result in enormous changes in transformer parasitic effects. >

Power density of piezoelectric transformers improved using a contact heat transfer structure

Abstract: Based on contact heat transfer, a novel method to increase power density of piezoelectric transformers is proposed. A heat transfer structure is realized by directly attaching a dissipater to the piezoelectric transformer plate. By maintaining the vibration mode of the transformer and limiting additional energy losses from the contact interface, an appropriate design can improve power density of the transformer on a large scale, resulting from effective suppression of its working temperature rise. A prototype device was fabricated from a rectangular piezoelectric transformer, a copper heat transfer sheet, a thermal grease insulation pad, and an aluminum heat radiator. The experimental results show the transformer maintains a maximum power density of 135 W/cm3 and an efficiency of 90.8% with a temperature rise of less than 10°C after more than 36 h, without notable changes in performance.