Isolation transformer

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

Ferroresonant voltage regulating circuit

Abstract: A ferroresonant voltage regulator circuit includes a non-saturating transformer, a linear reactor in series with the input, and a capacitor across the non-saturating transformer. Voltage sensing and referencing circuits are inserted in the output. A synchronous switch -- usually a saturable reactor, a magnetic amplifier, a triac or back-to-back SCR's -- is connected in shunt across at least a portion of the non-saturating transformer, and is controlled by its control coil in a manner such that the non-saturating transformer is loaded by the shunt loop at no-load conditions of the regulator. The control coil of the synchronous switch is connected in the voltage sensing and referencing circuits, and acts so that the amount of loading on the non-saturating transformer from the synchronous switch varies substantially inversely as the amount of loading because of the load on the voltage regulator circuit. A linear reactor may be series connected with the synchronous switch in the shunt loop. The non-saturating transformer has an air gap in its iron core so that it has a considerably more linear volt-ampere vs. flux density characteristic of the core and the air gap than that of a similarly rated and constructed saturating transformer.

Zeroing transformer's DC current in resonant converters with no series capacitors

Abstract: DC current unbalance in the windings of a transformer may initiate a runaway process and ultimately drive the transformer into saturation. Such a situation could arise in a transformer coupled resonant converter that does not include a series capacitor. This issue was explored in this study theoretically, by simulation and experimentally. A method is proposed for automatically adjusting the transformer's DC current to zero by correcting the asymmetry of the drive. This balancing control is facilitated by a signal obtained from a DC/AC current sensor which senses the transformer's primary and secondary currents such that they cancel each other for the no DC case. The proposed method was tested on a self oscillating, parallel loaded DC-DC resonant converter of 12V input voltage 500V output voltage and 700W power level. The proposed approach allows the design of resonant converters without DC decoupling capacitors which could lead to a significant cost and size reduction.

Automatic current overload protection circuit for electrostatic precipitator power supplies

Abstract: An automatic current overload protection circuit for electrostatic precipitator power supplies of the type utilizing a ferroresonant transformer. A low voltage tertiary winding in association with the transformer provides an output voltage to a sensing circuit for inhibiting current flow into the primary of the transformer when the tertiary voltage falls below a predetermined threshold. Another output voltage developed in association with the high voltage secondary winding of the transformer is also utilized to independently inhibit current flow into the primary of the transformer when the secondary voltage falls below a predetermined threshold. A time delay may be provided to permit operation of the overload protection circuit only in the event of a sustained overload current condition.

Reduction of Vibration and Sound-Level for a Single-Phase Power Transformer With Large Capacity

Abstract: This paper presents the reduction of noise and vibration concerning the magnetostriction effects for a single-phase power transformer with a large capacity of 200 MVA. Two magnetic core shapes are investigated: 1) D-yoked core and 2) square-yoked core. The D-yoked core is used for the construction of the transformer prototype in this paper. The magnetostriction and the hysteresis loop of the core material are measured for the simulation and analysis of noise and vibration. The transformer prototype is assembled with an external clamping force applied on the core, and the core vibration and sound-level are observed. The transformer operates with a periodic excitation that may induce resonance in the core. To avoid this, a finite-element analysis is used for modal analysis to identify the natural frequencies of the core. A tank is also designed with a sufficiently rigid structure to avoid resonances. The sound-level of the fully assembled transformer prototype is measured, and it is found to have a low-noise level below 65 dB.