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DC microgrid systems with hybrid energy resources are of significant interest in shipboard and spacecraft applications. In such a system, coordinated operation of circuit breakers (CBs) and disconnecting switches (DSs) can rapidly isolate short-circuit faults and restore the system very fast. In this paper, we investigate a new protection scheme for a Multi-Bus dc systems based on an event classification approach. The proposed protection scheme transfers less data when compared with commonly used data-based protection methods and does not require high-speed communication and synchronization. The results show that the developed protection scheme is able to identify the type of fault accurately, isolate the faulted area, and restore the system very quickly while maintaining continuous power to the loads. [ABSTRACT FROM PUBLISHER]

The article discusses the feasibility study of using time-and frequency-domain dielectric spectroscopy techniques in monitoring the fabrication of Oil-Impregnated Paper (OIP) condenser bushings. It states that non-graded and capacitance-graded bushings are the essential elements of power equipments such as circuit breakers, capacitors, and reactors. The stages of the manufacturing process include fabrication, drying, and impregnation. It finds that the measurements provide comprehensive evaluation of the insulation condition than the measurements at power frequency, with methods that are sensitive to moisture contents, voids, and short-circuits.

A capacitor in series with a transmission line is protected from overvoltage due to a large fault current by a nonlinear metal-oxide varistor (MOV) connected in parallel. Fault analysis, as well as the evaluation of performance of the transmission protection system, in the presence of MOV action becomes complex because 1) v-i characteristics of the MOV are nonlinear; 2) unsymmetrical MOV action for unsymmetrical faults will introduce coupling in sequence networks; and 3) MOV action will influence voltage or current inversion phenomenon. This paper presents a computationally efficient and simple methodology for fault analysis wherein the linear part of the network is modeled by an equivalent multiport Thevenin network. The proposed approach handles nonlinearity in fault analysis efficiently. It also provides an elegant approach to model unbalance in a network due to MOV action. The proposed approach can be used to determine relays prone to voltage or current inversion. Results on a real-life 716-bus Indian system illustrate the efficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a phasor measurement algorithm for transmission systems compensated with shunt capacitor banks. Since the shunt capacitor banks tend to lower the resonant frequencies, the dominant component, which has the lowest resonant frequency, is insufficiently attenuated by a low-pass filter and has an adverse influence on the phasor measurement of the fundamental component in a fault current signal. This paper theoretically investigates the dominant frequency in the presence of shunt capacitor banks and presents a phasor measurement algorithm immune to the dominant component and DC-offset. The performance of the algorithm is evaluated for a-phase to ground (a–g) faults on a 154-kV transmission system compensated with shunt capacitor banks. The evaluation results indicate that the algorithm can measure the phasor reliably and satisfactorily, although the fault current signal is distorted with the dominant component and DC-offset. The paper concludes by describing the hardware implementation of the algorithm on a prototype unit based on a digital signal processor. [Copyright &y& Elsevier]

Pulsed mechanical loads on objects are produced upon an electrical explosion of metal foils with an area of <400 cm2. A bank of 48 ИК 100-0.4 УХЛ4 capacitors is mounted in four metallic tanks with oil insulation and stores an energy of up to 96 kJ. Each two capacitors are switched by a thyratron and transfer a current along a cable line to a common electrical explosion unit. Twenty-four spark gaps operate with a time spread of ±3 ns relative to the trigger pulse and have an electric strength margin of ∼80%. The total inductance of the circuit is ∼70 nH. The discharge current amplitude reaches 1.68 MA, and its oscillation quarter-period lasts ∼1.8 µs. Various designs for the electrical explosion unit, based on an aluminum foil 7 µm thick, and methods for measuring the mechanical impulse values are described. The distribution of impulse over the foil area is controlled by the number of exploded foil layers. All of the test bench units can be transported and promptly put into operation at a new site. [ABSTRACT FROM AUTHOR]

Self-excitation type switching elements have made remarkable progress in recent years and their high-speed switching capability and low loss characteristics have made it possible to use them for many purposes. They are especially useful for raising the frequency of voltage source type inverter. In the forced commutation mode, however, the commutation voltage is supplied from the commutating condenser and the commutating condenser absorbs the energy stored in the leakage inductance on the ac side. If the forced commutation type phases controlled thyristor bridge is used for a high power circuit, a large capacity commutation condenser has to be used, which requires such floor space and expensive equipment.

This paper proposes a fault current limiter (FCL) of resonant type. The FCL consists of a capacitor and a reactor. The inductive reactance of the reactor is controlled by a spark gap. The operating principle of the FCL is based on producing a large current-limiting impedance in the fault system network. The current-limiting effect of the FCL is examined by experiment and Alternate Transients Program simulation, which shows that such a limiting device can reduce the fault currents significantly during short-circuit faults. [ABSTRACT FROM AUTHOR]