J. Lim

Bio: J. Lim is an academic researcher from Westinghouse Electric. The author has contributed to research in topics: Inductor & Voltage. The author has an hindex of 1, co-authored 1 publications receiving 24 citations.

Corona Measurement and Interpretation

Abstract: This discussion of the performance of the more common types of corona measurement circuits has emphasized certain points. They may be summarized as follows: 1. The coulomb charge in individual corona discharges and the number and phase of these individual discharges are considered the significant quantities in corona measurement. 2. The voltage step pulse produced by a single discharge varies directly as the pulse coulomb charge and inversely as the test specimen capacitance and the capacitance in parallel with it. This voltage is then divided between the detector input shunt capacitance and the series-coupling capacitance. 3. The observed shape of the pulse following the very rapid step change in voltage is determined by the inductance or resistance shunting the detector input. These produce, in the case of a resistance, a nonoscillatory exponentially decaying voltage, and in the case of an inductor an oscillatory decaying voltage. 4. A wide-band amplifier is needed to indicate a major fraction of the initial pulse height if the time constant of the exponential decaying is short. This is particularly true of the nonoscillatory pulse produced by a resistance input, where conventional narrow-band amplifiers have an output crest voltage which is only a small fraction of the input pulse crest. A much greater sensitivity may be achieved with a fairly narrow bandwidth amplifier tuned to the natural oscillation frequency of the input circuit having an inductance. A high Q in this input circuit is preferred to give maximum sensitivity. 5.

Fundamental Limitations in the Measurement of Corona and Partial Discharge

Abstract: The theoretical sensitivity of conventional partial discharge detectors is compared with that obtained from ultra wideband (UWB) (up to l GHz) detection systems. The comparison indicates that for relatively lossfree distributed systems, such as SF6 insulated bus, the UWB system is up to two orders of magnitude more sensitive. UWB detection also embodies additional advantages such as facilitating the location of discharge sites and the rejection of external electrical noise. For discharge detection in plastic-insulated cables, true UWB detection is not practical because of frequency-dependent attenuation effects, although certain gains in sensitivity can be achieved with a detector bandwidth of up to 10 MHz.

Partial discharge. XVII. The early history of partial discharge research

Abstract: For pt.XVI see ibid., vol.9, no.3, p.21 et seq. (1993). Early investigations into partial discharge (PD) phenomena are reviewed to illustrate how little has changed and how much has, in some respects, been repeated during the forty years from 1940 to 1980. The early days of PD research included studies of PD in gas-filled cavities in oil-impregnated paper insulation, broad studies of PD in high voltage apparatus and dielectric materials, and research into PD in turbine generator insulation systems. The development of PD test techniques, development of test apparatus, and development of PD-related standards are discussed. >

The Relation of Capacitance Increase with High Voltages to Internal Electric Discharges and Discharging Void Volume

Abstract: A practical means of estimating the fractional volume of gas space in insulation from high-voltage capacitance and dissipation factor measurements has been suggested in this paper. This method has been evaluated by tests on models and various high-voltage insulation specimens. An analysis has been derived relating the observed a-c capacitance and dissipation factor increase with high voltages to the individual electric discharges between the surfaces of gas spaces in insulation.

Radio Frequency Sensing of Incipient Arcing Faults within Large Turbine Generators

Abstract: Sensing of incipient faults within large turbine generators (> 500 MW) is very important because a persistent minor abnormality may suddenly develop into a major fault and cause extensive damage before conventional early warning sensors can respond. Consequently, there is a need for a reliable sensing system which will respond to the early arcing stage of a fault, when insulation surfaces are not at a sufficiently high temperature to emit particulates and activate the conventional Core or Generator Condition Monitor.