Isolation transformer

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

The Impact of Current-Transformer Saturation on Transformer Differential Protection

Abstract: Current-transformer (CT) saturation has a major impact on the operation of differential protection schemes. Transformer differential protection must maintain security during CT saturation for external faults while preserving high sensitivity and speed of operation for lower magnitude internal faults. Relay manufacturers provide very little information or direction for protection engineers to set relays adequately to achieve these goals. If an engineer lacks a deep understanding of relay behavior during CT saturation, he or she could make setting implementation mistakes that may lead to spurious trips or failures to trip with catastrophic consequences. This work investigated the impact of CT saturation on transformer differential relays in order to provide guidance on scheme behavior. It was discovered that harmonic blocking is triggered by CT saturation—a significant effect which is not described in the literature or relay manuals. This effect was modeled and the model's accuracy was verified with CT simulations, relay secondary injections, and high current primary injections. It is demonstrated that harmonic blocking provides effective security against nuisance trips caused by CT saturation. It is also shown that the traditional use of a high slope 2 is mostly redundant wherever harmonic blocking is enabled.

Grounding of AC and DC low voltage and medium voltage drive systems

Abstract: The grounding of AC and DC motor drive systems should detect and clear ground faults both on the source and load side of the power converters. Most drive systems are separately derived through a step-down transformer, which serves as a drive isolation, as well as rectifier transformer. Isolation transformers on individual or group drive systems, downstream of main substation transformers are also common. An output isolation transformer on an AC drive will isolate the drive electronics, step up the AC voltage from the inverter section and also serve to control high line-to-ground voltages on the motor windings. The grounding system has a profound effect upon the continuity of operations, loading of the solid-state devices and common-mode voltages. This paper discusses the various possibilities of grounding of low-voltage and medium-voltage motor drive systems and shows that a high-resistance grounding system can be often implemented to permit continuity of operations, allow fault detection and limit the transient overvoltage.

Boost mode power conversion

Abstract: Boost Mode Regulator techniques are used to provide regulated a.c. or d.c. output from a.c. or d.c. sources. One embodiment involves regulation of the output of an a.c. source to provide a regulated d.c. voltage. The source inductance becomes part of the boost mode circuit, thus avoiding the losses associated with the addition of external inductors. When a three-phase alternator is the power source, the circuit comprises a six diode, three-phase rectifier bridge, three FET transistors and a decoupling capacitor. The invention involves shorting the output of the power source to allow storage of energy within the source inductance. During this time, the decoupling capacitor supports the load. When the short is removed, the energy stored in the inductances is delivered to the load. Because the circuit uses the integral magnetics of the source to provide the step-up function, the efficiency of the design can be quite high. In another embodiment, the leakage inductance of an isolation transformer is used to provide regulated a.c. or d.c. outputs from an a.c. source and to provide regulated a.c. or d.c. output from a d.c. source. Where a d.c. source is used, chopper circuits are used on the primary side of the transformer. The invention provides for regulation of the output voltage or for maintaining a power factor substantially close to unity.

Constant current source employing power conversion circuitry

Abstract: An energy source for supplying power to a rechargeable battery or the like provides a constant current input to the front end of a transformer. In order to compensate for varying inductances found in the primary winding of the transformer, a special resistor network is provided to precisely control the duty cycle of the current output.

Multi-level data transmitter

Abstract: A data transmitter circuit includes a pseudoternary conversion circuit for converting a binary logic signal to a differential pseudoternary signal having symmetric rise and fall characteristics The output of the pseudoternary conversion circuit is filtered and passed to an electrically conductive medium via an isolation transformer The conversion circuit includes a symmetric arrangement of toggle circuits which respond to transitions in respective complementary binary signals constituting a differential binary input signal Voltage dividers are connected to the output terminals of the toggle circuits for providing three levels of output voltages in response to the logical states of the toggle circuits