Isolation transformer

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

High voltage power transformer insulation design

Abstract: The large power transformer life span depends heavily on insulation — its condition, materials, composition, geometry, etc. The high voltage transformer insulation requires a very focused analysis in the design stage. The large power transformer is subjected to different overvoltages during factory testing and in operation, therefore all resulting electric stresses have to be modeled in the electric field program and compared to the industry accepted withstand curves. The overvoltages include transient voltages from impulse testing, both lightning and switching, as well as power frequency voltages generated during the induced and applied voltage tests. The distributions of electric stresses under these different electric excitation conditions are different. The transient voltage programs with MLCR components (mutual- and self-inductance, capacitance, resistance) are used to establish exact voltage distribution inside the transformer. The electric field analysis for complex units is performed for all energized components, including turn-to-turn, section-to-section, winding-to-winding, winding to core, phase-to-phase, between leads, from winding and leads to constructional parts, bushing to tank, etc. The electric stresses are checked under two main conditions: (i) strike in oil, (ii) creeping discharge along solid insulation. The paper will discuss the analysis for selected transformers and explain the design process needed to maintain the dielectric stresses under critical values.

Fault detection apparatus for a transformer isolated transistor drive circuit for a power device

Abstract: A protection circuit which electrically isolates logic level and high-side circuits and detects high side power device fault conditions at the isolated, logic level side of the circuit. When an overvoltage or overcurrent condition occurs at the power switching device, a protection circuit disables the conduction of current through the current carrying terminals of the switching device, preventing damage from occurring to the device. Activation of the protection circuit effects an increased current flow in the secondary and primary coils of the isolation transformer between the low side and high side elements. Voltage at the primary coil of the isolation transformer is monitored by low level circuitry to detect the rise in current, indicating a fault to the system controller upon detection.

Rotary transformer design

Abstract: A high power rotary transformer (1 k W ) was considered as a replacement for slip-rings in a future satellite. A study was done to determine the best electrical design taking into account mechanical limitations while maximizing efficiency. Ferrite was used in a configuration which can be ground by any good machine shop. A design procedure is described which provides the engineer with a rough estimate of size and weight of a near optimum transformer given the power level, frequency of operation, and material to be used. The electrical circuit used should be considered during the transformer design. In the widely used voltage controlled push-pull square wave converter there is the problem of transistor storage and fall time. Usually one transistor is turned on before the other is off. The latter transistor then traverses through a high power dissipation region, the peak power being twice the input voltage times input current. Transistors picked for low saturation voltage are usually slower devices aggravating the turn-off dissipation problem. An operating procedure which minimizes these turn-off losses and prevents excursion through high instantaneous dissipation regions has been devised. It allowed the construction of a 1000 watt converter (dc-dc rotary transformer) which runs at a 92% efficiency (including rectifier losses) with just a total of 10 watts of transistor dissipation. Operating levels are 24 volts, 50 amps in and out.