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The features of algorithms and apparatus for determining the parameters of passive multicomponent two-terminal networks with a short circuit between the poles through an inductive component and a dc break in the circuit are considered. The measuring circuit is supplied with voltage pulses varying as a function of the nth power of time and n-fold differentiation of the signals at the input and output of the circuit. Generalized parameters of the transfer function are calculated in terms of the ratio of the signals in each differentiation channel. [ABSTRACT FROM AUTHOR]

Busbar technology is more and more used to realize connections within power supply systems in answer to the need of compactness. The integrated problem on heat conduction and radiation-convective heat exchange describes the temperature regime in current conductors and current carrying busbars of power electrical apparatus such as circuit breakers or high breaking capacity fuses. Beside steady-state conditions, the transient thermal regime of busbar has an important influence upon whole power supply system from thermal behaviour point of view. Hence, an on-line temperature monitoring system of busbars has been developed. Also, the thermal transient impedance for the busbar has been computed. This allows a better correlation between protection characteristics of the fuse and circuit breaker and busbar design. [ABSTRACT FROM AUTHOR]

For each transformer, windings and insulations are the most important elements economically and technically, so highly protection should be considered for them. The main fault that occurs in a transformer is internal short circuit through the winding, which may lead to serious damage in winding on transformer including winding deformation, interruption or even the explosion of the transformer because of oil's overheating. Consequently, winding need to be frequently checked to avoid major damages. In this paper, a new method for modeling and simulation of transformer's winding fault has been presented. According to happened variation in line current and evaluation of its symmetrical component (positive, negative and zero sequences), easy and precise algorithm has been obtained that can be used for simulation of internal fault of transformer's winding. The algorithm has been implemented for winding faults and has been simulated by MATLAB/SIMULINK software. [ABSTRACT FROM AUTHOR]

This paper deals with a method for the design of a fault-tolerant control system based on the Generalized Internal Model Control (GIMC) structure, consisting of a standard outer loop feedback controller and an extra inner loop controller. The distinguishing feature of the GIMC structure is that controller design for performance and robustness may be performed separately. The outer loop controller is designed for nominal performance using some controller synthesis to meet the (nominal) control specification, while the inner loop controller is designed to make a trade-off between robustness and performance. This feature is suitable for fault-tolerant control. The outer loop controller is designed for the fault-free case, and the inner loop controller for the fault-time case. In the conventional methods, the inner loop controller is designed to maximize the robust stability margin without fault information. Therefore, the performance in the fault-time case tends to become conservative. In this paper, the inner loop controller is directly designed from experimental data collected from the faulty system. Since the collected data contains information on the fault, conservativeness in the conventional methods is decreased. The inner loop controller is designed by Virtual Reference Feedback Timing (VRFT). VRFT is a method of direct design from input-output data without identifying any models. Since the complexity of the controller can be specified by the designer, no complexity reduction is necessarily required, which is advantageous in implementation. The effectiveness of the proposed design method is confirmed by an experiment. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(4): 53–62, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20929 [ABSTRACT FROM AUTHOR]

Photovoltaic generation systems must have protection devices and islanding detection devices if they are connected to utility lines of the electric power company. This is regulated in national technological requirement guidelines and the electric equipment technology standards. Islanding detection devices are installed to detect blackouts due to events such as ground faults and short circuits in utility lines. When an islanding detection device detects a power blackout, the photovoltaic generation system must be stopped immediately. It is known that islanding detection devices cannot detect islanding if induction motors are present among the loads. We investigated the influence of induction motors on islanding detection devices and found that when the frequency decreases after a utility line failure, induction motors change over to generator mode, thus compensating the active power imbalance and suppressing voltage variation. In addition, if the postfault frequency is adjusted by PLL control so as to maintain a fixed power factor, induction motors suppress this frequency change, thus extending islanding operation. It is clear from the above results that induction motors are more likely to produce islanding phenomena than static loads. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(4): 8–18, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20962 [ABSTRACT FROM AUTHOR]

Dynamic Voltage Restorer (DVR) is a cost effective approach for the protection of sensitive consumers from voltage sags. Voltage sags always happen in a few times and are related with short circuit events and starting motors which needs high lagging current. Implementations of the DVR at a Medium Voltage (MV) level give an opportunity, to protect large sensitive loads from voltage sags. The control of DVR with Sliding Mode Control (SMC) method makes it multi-purpose for the compensation of the voltage sag, swell, flicker and harmonics. In this paper, the minimum energy injection concept has been used for restoration during DVR compensation. Analysis and simulation using MATLAB has been shown that the voltage is perfectly controlled across the critical load. The simulation results have been compared with the experimental results, which verify the capabilities of the proposed control method. [ABSTRACT FROM AUTHOR]

This paper presents the study of impact of sliding mode control speed on the diagnosis process in a short circuit stator. The sliding mode controller is model based approach used to improve the robustness of the control low despite the high influence of the motor parameters and to illustrate the good performance of this technique. These modes of regulators are insensitive with the parametric variation. However, we present a methodology of monitoring of defaults of short-circuits to the stator of a synchronous motor permanent magnet. [ABSTRACT FROM AUTHOR]

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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.

The matrix converter (MC) presents a promising topology that needs to overcome certain barriers (protection systems, durability, the development of converters for real applications, etc.) in order to gain a foothold in the market. Taking into consideration that the great majority of efforts are being oriented toward control algorithms and modulation, this paper focuses on MC hardware. In order to improve the switching speed of the MC and thus obtain signals with less harmonic distortion, several different insulated-gate bipolar transistor (IGBT) excitation circuits are being studied. Here, the appropriate topology is selected for the MC, and a recommended configuration is selected, which reduces the excursion range of the drivers, optimizes the switching speed of the IGBTs, and presents high immunity to common-mode voltages in the drivers. Inadequate driver control can lead to the destruction of the MC due to its low ride-through capability. Moreover, this converter is especially sensitive during start-up, as, at that moment, there are high overcurrents and overvoltages. With the aim of finding a solution for starting up the MC, a circuit is presented (separate from the control software), which ensures correct sequencing of supplies, thus avoiding a short circuit between input phases. Moreover, it detects overcurrent, connection/disconnection, and converter supply faults. Faults cause the circuit to protect the MC by switching off all the IGBT drivers without latency. All this operability is guaranteed even when the supply falls below the threshold specified by the manufacturers for the correct operation of the circuits. All these features are demonstrated with experimental results. Lastly, an analysis is made of the interaction that takes place during the start-up of the MC between the input filter, clamp circuit, and the converter. A variation of the clamp circuit and start-up strategy is presented, which minimizes the overcurrents that circulate through the converter. For all these reasons, it can be said that the techniques described in this paper substantially improve the MC start-up cycle, representing a step forward toward the development of reliable MCs for real applications. [ABSTRACT FROM AUTHOR]

A two-step method is applied for parameter identification of a saturated electromechanical model of an induction machine (IM). The k-factor cross saturation technique is used to account for iron saturation. Balanced and unbalanced short-circuits armature current waveforms of this machine are less sensitive to variations in the mechanical parameters. Conversely, any change in these parameters has a strong impact on the start-up test. Accordingly, in the proposed estimation method, the online double-line-to-neutral short-circuit test is performed to estimate the electrical parameters of the machine and the results obtained are then used to compute the mechanical parameters from the starting test. The good agreement of the estimated results with actual data attests to the effectiveness and suitability of the proposed algorithm in computing the electromechanical parameters of these machines. [ABSTRACT FROM AUTHOR]

This paper introduces a procedure for using optimization-enabled electromagnetic transient simulation (OE-EMTS) for the design of HVDC system controls. The OE-EMTS method con- ducts a sequence of simulation runs of the network, guided by a nonlinear optimization algorithm. The controller parameters in each subsequent run are refined with the aim of achieving a desired performance measure, mathematically represented by an objective function (OF). The paper demonstrates a design procedure, in which the selection of the OF follows an evolutionary path. The system is first designed with an initial OF, which often results in some unforeseen negative system behavior. In the next stage, a new OF is selected, which has the potential for mitigating this negative behavior. This cycle is terminated when a high-quality design is achieved. The procedure is exemplified with the controller design for a 200-MW back-to-back dc scheme to operate within a range of inverter short circuit ratios. The optimality measure considers dynamic changes in controller set-points as well as recovery from faults. [ABSTRACT FROM AUTHOR]

The design and implementation of a new control scheme for reactive power compensation and voltage regulation in the transmission system, as provided and controlled by a wind park is presented. It proposes an optimal tracking secondary voltage control scheme applied to doubly fed induction generator-based wind generators. The ability of the controller to regulate transmission network voltage profiles is demonstrated and compared with primary voltage control, an alternate secondary voltage control approach, and the voltage profile obtained from optimal power flow analysis. The dynamic performance of the controller is also validated in response to system contingencies, namely short circuits. The impact of communication time delays and of the short-circuit ratio on the dynamic performance of the voltage controller are considered. Results show that the controller properly regulates the voltage in steady state and performs properly during transients resulting from short circuits. Decoupling between primary and secondary loops should be applied to mitigate the effects of the time delay. [ABSTRACT FROM AUTHOR]

The adjunction of constrictions along the meander of a superconducting Fault Current Limiter (FCL) greatly improves its behavior thanks to a better distribution of the dissipative zones at the occurrence of a short circuit. This design works perfectly for symmetrical short circuit (i.e. short circuit at the maximum voltage). However for asymmetrical short circuits (at voltages close to 0), we are facing a problem due to the small number of the initially switched constrictions. To solve this problem, we test the possibility to speed up the transition into the normal state of the whole meander by heating it locally. This thermally assisted transition is realized by growing a gold layer on the backside of the substrate and by patterning it into a meander with its dissipative parts lying just underneath the constrictions of the FCL. This gold meander can be either connected in parallel with the superconducting me- ander or a capacitor bank can supply the current. In order to confirm the benefit of the thermally assisted transition we have carefully measured the behavior of the FCL during constant current and low voltage pulses as a function of the power injected into the gold line. We present results showing that the response of the FCL to the generated heat is very fast; typically less than 100 μs. Furthermore the distribution of the dissipated power across the wafer, during asymmetrical AC short circuit, is clearly improved. [ABSTRACT FROM AUTHOR]

This study focuses on a compact vacuum circuit breaker (CB) for nominal voltage of 72.5 kV, nominal current of 2000 A and short circuit current of 31.5 kA. The dielectric conception of the vacuum interrupter (VI) is based on a multiple floating shield configuration which reduces the risk of total breakdown due to partial breakdown between the contacts and shield. An optimised electrical field distribution on the contact surface with the maximum field pointing towards the floating shield is arranged and hence reducing the breakdown effective area of the contacts facing each. All tests have been performed on a specially designed single-phase circuit breaker pole-unit equipped with a low energy spring type mechanism. Interruption performance was confirmed in direct tests. The circuit-breaker pole was proved to be restrike-free with respect to cable charging class C2. Dielectric tests in new condition and after interruption tests confirmed the announced ratings. These tests confirm the feasibility of this HV-CB with 25% more compact Vi's based on the outlined dielectric conception. [ABSTRACT FROM AUTHOR]

One of the most important factors in an artificial pollution test of transmission and distribution insulators of power systems is the short-circuit current of the source. Most laboratories do not have strong source and test transformers. In this paper a test setup has been introduced to improve the performance of high-voltage laboratories for pollution test. It is based on adding an output capacitor and compensator reactors in a cascade setup. Beside simulations, clean-fog test method was used to determine the flashover voltage (FOV) of insulators that selected from overhead lines. Using the developed setup, there is an error in FOV less than 30% compared with a stiff setup in light pollution for ceramic cap and pin insulators. Higher levels of pollution cause the higher error in FOV in all cases. Although the error increases with pollution level, it is smaller in the case of composite insulators. The error decreases depending on the hydrophobicity of silicon rubber. So the less hydrophobic the insulator surface, the greater the error in FOV. [ABSTRACT FROM AUTHOR]

Electromechanical circuit breakers based on micro-electromechanical systems (MEMS) structures are proposed, and initial prototypes are demonstrated. The devices use laterally moving thermal actuators to set and trip low resistance contacts. The actuators are fabricated from electroplated Ni, on Si substrates, with Au-Co contact layers. Trip currents of 300 mA are obtained, with contact resistances below 1 Ω. Rapid tripping (below 50 ms) is achieved, even for modest over-current levels, and sensitivity to ambient temperature is much less than for positive temperature coefficient (PTC) devices typically used for over-current protection in electronics applications. These MEMS devices offer an ultra-miniature, potentially low cost solution for circuit protection applications at low currents, where a high degree of system control is desired. [ABSTRACT FROM AUTHOR]

Arcing faults on 600/347-V underground cables can cause considerable damage, even explosions, despite the installed protection system. In fact, the protection sometimes appears to be quite slow to operate considering the prospective short circuit. Laboratory tests provided an opportunity to better characterize these arcing faults and prove that they can be intermittent. They can be quite random in nature, usually comprising periods of conduction lasting one half-cycle separated by periods of nonconduction lasting from a few cycles to several minutes. This type of fault can easily make fuse-type protection ineffective, as other tests proved. The fuse operating time can become even longer, to the extent that explosive gases will form. [ABSTRACT FROM AUTHOR]

Historically the analysis of pulsed magnets has indicated that a coil assembly comprised by a layer-by-layer graded conductor coil is nearly optimum. Additionally the layer-to-layer winding transitions, associated with monolithic coil construction, are problematic and often the source of catastrophic failure in pulsed coils. FEA analysis of transition structures has confirmed the lessons of operational experience. Additionally the layer-to-layer winding transitions present an unacceptable risk a short circuit fault to the reinforcement structure. These attributes of monolithic coil construction have limited the fields where pulsed magnets can be operated to approximately 60 T. Several operational issues arise above this field: coil reliability degrades, and the time required to cool the magnet between shots is increased, since higher field monolithic coils require large amounts of distributed internal reinforcement to limit conductor strain. We are developing a new `poly-layer' coil construction to address these engineering requirements. In this construction, each layer is wound separately on a forming mandrel, and then installed onto an assembly mandrel. Spool pieces are installed at each end to support the lead exits as they transition out of the windings. Each layer is joined in series with the next in a joint structure that is constrained in the radial and circumferential directions, but free to move with the coil in the axial direction. Furthermore, the coil reinforcement is used to support the lead in the transition region between the windings and the joint. The new design represents a change in our manufacturing template that is intended to allow development of higher field coils. This paper will report design details and the results from prototype testing. [ABSTRACT FROM AUTHOR]

A subharmonic injection-locked balanced oscillator is presented in this paper. Subharmonic injection locking is preferred to fundamental injection locking, because the central injection point is a virtual short-circuit at the fundamental frequency for a balanced oscillator. An analytical model is described to predict the locking range whereby power series are used to model the device's nonlinearity. An injection-locked balanced oscillator is designed at 5.8 GHz and very good agreement is achieved between the predicted and measured locking ranges. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 306–309, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20124 [ABSTRACT FROM AUTHOR]

Fault analyses are performed for the interconnecting system between a commercial-scale subsonic diagonal-type MHD generator and an ac power system through a line-commutated inverter. The behavior of the interconnecting system is first examined for the case of single misfiring of one thyristor in the inverter. In this case, the load current increases because the inverter system is short-circuited. Following the theory of inverter commutation, the load current decreases to the rated value and the MHD generator is restored to the rated condition. Next, the cases of a single-line ground fault and of a three-phase short circuit fault are investigated. The line voltage decreases and thus the load currents increase after the fault. This increase of load currents destroys the design-point flow of the MHD generator. Phase-control angle control of the inverters is required in order to restore the rated operation of the MHD generator. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 29–36, 2001 [ABSTRACT FROM AUTHOR]

The transmission and reflectivity of electromagnetic energy across a planar layer consisting of periodic arrays of convoluted loop elements (with interelement spacing of 6.08 cm) is investigated in the lower microwave spectrum at 1.575 GHz (λ=19 cm). This relatively close spacing is achieved by convoluting the conventional 1λ square loop element at its four corners. The close interelement spacing provides a stable passband frequency response over wide angles of wave incidence, while the convoluted segment provides a short circuit response when the segment length is λ/4 long. The short circuit will provide a reflection to the electromagnetic energy at the selected band-stop frequency range. Various design considerations have been adopted to meet the challenge of ensuring a common passband bandwidth of 22.47% (1.5–1.95 GHz), with a transmission loss of less than 0.5 dB for scan angles up to 45° in both TE and TM polarization. [ABSTRACT FROM AUTHOR]