Voltage Oscillation Frequency Research Articles

Influence of external AC transverse magnetic field on air arc oscillation patterns and its application in DC forced current zero techniques

Abstract Direct current (DC) circuit breakers are essential for maintaining the stability of the electric energy transmission and safeguarding the power equipment from the damage caused by the fault currents in DC power systems. The characteristics of the switching arc can be utilized in DC forced current zero techniques. This paper investigates the influence of an external alternating current (AC) transverse magnetic field on the oscillation characteristics of air arc. By confining the arc between two insulating walls and applying a transverse AC magnetic field, the arc exhibits ‘bidirectional oscillation’ and ‘unidirectional oscillation’ modes. The effects of magnetic field amplitude and frequency on the air arc oscillation characteristics are analyzed through experiments, from the aspects of the arc voltages and arc motions. It can be found that an external AC magnetic field can stabilize the arc voltage at a specific oscillation frequency. By connecting an inductor–capacitor (LC) branch in parallel with the arc and setting the LC branch’s resonant frequency equal to the arc voltage oscillation frequency, a current resonance process between the arc and the LC branch can be achieved. This resonance facilitates the creation of the arc current zero-crossing point. A test platform based on the arc oscillation characteristics is established for current interruption experiments. For system currents of 1 kA and 3 kA, the arc current zero-crossing time is controlled within 0.41 ms after applying the external AC transverse magnetic field. The experimental results verify the rationality of the proposed DC breaking scheme.

Analysis and suppression of voltage oscillation at DC circuit breaker terminal in DC fault transient process

High-frequency voltage oscillation occurs at the initial stage of DC short-circuit fault in the modular multilevel converter (MMC)-based high-voltage direct-current systems, which directly threatens the reliable operation of the secondary equipment in DC circuit breakers (DCCBs). Therefore, this paper focusses on the voltage oscillation characteristic at DCCB terminals, considered the stray parameters of connecting lines, the parasitic parameters of main equipment and the impedance of grounding grid, established equivalent circuit models of MMC-HVDC converter station at the initial stage of pole-to-pole and pole-to-ground fault, and obtained the analytical formula for the voltage oscillation frequency. Then, the comparison with the DC short-circuit test data of ±200 kV MMC-HVDC converter station verified the validity of the models and revealed the mechanism of voltage oscillation. Finally, the influence of the parameters of the converter station on the oscillation characteristics was discussed. It was proposed to install the DCCB at the MMC valve's terminal near the DC side, and the oscillation frequency is about 10–60 kHz, which is more than 5 times lower than that at the DC reactor's terminal near the DC pole bus, and the disturbance of oscillation to DCCB was alleviated.

Strong Parametric Coupling between Two Ultracoherent Membrane Modes.

We demonstrate parametric coupling between two modes of a silicon nitride membrane. We achieve the coupling by applying an oscillating voltage to a sharp metal tip that approaches the membrane surface to within a few 100nm. When the voltage oscillation frequency is equal to the mode frequency difference, the modes exchange energy periodically and faster than their free energy decay rate. This flexible method can potentially be useful for rapid state control and transfer between modes, and is an important step toward parametric spin sensing experiments with membrane resonators.

Transition from Townsend to radio-frequency homogeneous dielectric barrier discharge in a roll-to-roll configuration

The aim of this paper is to better understand the transition from Townsend to radio-frequency homogeneous dielectric barrier discharge (DBD) at atmospheric pressure. The study is done in an Ar/NH3 Penning mixture for an electrode configuration adapted to roll-to-roll plasma surface treatment. The study was led in a frequency range running from 50 kHz up to 8.3 MHz leading to different DBD modes with a 1 mm gas gap: Glow (GDBD), Townsend (TDBD), and Radio-frequency (RF-DBD). In the frequency range between TDBD and RF-DBD, from 250 kHz to 2.3 MHz, additional discharges are observed outside the inter-electrode gas gap. Because each high voltage electrode are inside a dielectric barrel, these additional discharges occur on the side of the barrel where the gap is larger. They disappear when the RF-DBD mode is attained in the 1 mm inter-electrode gas gap, i.e., for frequencies equal or higher than 3 MHz. Fast imaging and optical emission spectroscopy show that the additional discharges are radio-frequency DBDs while the inter-electrode discharge is a TDBD. The RF-DBD discharge mode is attained when electrons drift becomes low enough compared to the voltage oscillation frequency to limit electron loss at the anode. To check that the additional discharges are due to a larger gas gap and a lower voltage amplitude, the TDBD/RF-DBD transition is investigated as a function of the gas gap and the applied voltage frequency and amplitude. Results show that the increase in the frequency at constant gas gap or in the gas gap at constant frequency allows to obtain RF-DBD instead of TDBD. At low frequency and large gap, the increase in the applied voltage allows RF-DBD/TDBD transition. As a consequence, an electrode configuration allowing different gap values is a solution to successively have different discharge modes with the same applied voltage.

Wave energy: Modeling and Analysis of Power Grid Integration

Wave energy could play a major role for diversification of the energy matrix in Latin America. However, it has impact on the stability of the power system. This paper studies the integration of a wave generation system in a power grid and its impact on the oscillations of frequency. A critical analysis is made about the real potential of this technology. Different cases are analyzed taking into account the injection level of power from the wave generator and the requirement of energy storage. Results demonstrate that high penetration of wave generation affects the frequency of the network and takes it out from the dead band considered in the Colombian regulation. Simulations on the IEEE 9 bus system shows that integration of a wave power generation system produces frequency drop, phase power and voltage oscillation as well as other dynamic problems in the power grid. However, when such integration is adequately planned, it is safe to inject power to the electrical system from a wave generation plant.

Measurement and analysis of transient overvoltage distribution in the low-voltage winding of 1000 kK power transformer without oil immersion

High frequency voltage oscillations will be generated when transient overvoltages intrude into power transformers. These oscillations may cause damage to the insulation of transformers. In this paper, a capacitive coupling sensor array was presented for measuring voltage distributions and voltage gradient distributions in low-voltage winding of a 1000 kV power transformer. A variable impedance transmission line between impulse generator and winding was also designed to avoid distortion of the applied impulses. The results indicate that under the lightning impulse voltages, voltage distributions have been restrained below applied voltage at sandwich-interleaved section but exceed the applied voltage in continuous coils in the first half of the winding and lead to a very nonuniform voltage distribution. Longer duration time will result in a more nonuniform distribution. The amplitude of the transient voltage under steep front square wave reduces faster downward the winding than that under lightning impulse voltages. A shorter rise time will lead to a much worse distribution. In addition, a dominated oscillation of 63 kHz is found under both impulse voltages and steep front square waves.

Six‐element circuit for maximum power point tracking in photovoltaic‐motor systems with variable‐frequency drives

AbstractA low‐cost circuit was developed for stable and efficient maximum power point (MPP) tracking in autonomous photovoltaic‐motor systems with variable‐frequency drives (VFDs). The circuit is made of two resistors, two capacitors, and two Zener diodes. Its input is the photovoltaic (PV) array voltage and its output feeds the proportional‐integral‐derivative (PID) controller usually integrated into the drive. The steady‐state frequency–voltage oscillations induced by the circuit were treated in a simplified mathematical model, which was validated by widely characterizing a PV‐powered centrifugal pump. General procedures for circuit and controller tuning were recommended based on model equations. The tracking circuit presented here is widely applicable to PV‐motor system with VFDs, offering an efficient open‐access technology of unique simplicity. Copyright © 2010 John Wiley & Sons, Ltd.

A Failure Mode for PWM Inverter-Fed AC Motors Due to the Antiresonance Phenomenon

A failure mode for pulsewidth-modulation inverter-fed ac motors due to the antiresonance phenomenon is introduced and investigated in this paper. At high frequencies, an ac motor behaves as a series RLC circuit with a resonance point, so-called antiresonance, typically above 1.0 MHz. If the voltage oscillation frequency caused by the reflected-wave phenomenon matches the motor antiresonance frequency, an amplified voltage will appear internally between the turns of the stator windings. This externally unobservable state can cause winding insulation failure in the ac motor. This phenomenon is experimentally verified using a rewound permanent-magnet motor with accessible taps along the stator windings, and the results are presented in this paper.

Instability and stable non-stationary state induced by current in stack direction in low-dimensional conductors

We have studied the problem of the current flow through the sample with narrow energy band when the average voltage corresponds to the negative differential conductance (NDC) region. We have found a stable solution in the NDC region which describes uniform high frequency voltage oscillations. Frequency of the oscillation is determined by antenna properties of the system. The results are applicable also to semiconductor superlattices.

Paul trap experiment to simulate intense nonneutral beam propagation through a periodic focusing field configuration

This paper describes the design concept for a compact Paul trap experimental configuration that fully simulates the collective processes and nonlinear transverse dynamics of an intense charged particle beam that propagates over large distances through a periodic quadrupole magnetic field. To summarize, a long nonneutral plasma column ( L⪢ r p) is confined axially by applied DC voltages V ̂ = const. on end cylinders at z=± L, and transverse confinement is provided by segmented cylindrical electrodes (at radius r w) with applied oscillatory voltages ± V 0( t) over 90° segments. Because the transverse focusing force is similar in waveform to that produced by a discrete set of periodic quadrupole magnets in a frame moving with the beam, the Paul trap configuration offers the possibility of simulating intense beam propagation in a compact experimental facility. The nominal operating parameters in the experimental design are: barium ions ( A=137); plasma column length 2L=2 m ; wall radius r w =10 cm ; plasma radius r p =1 cm ; maximum wall voltage V ̂ 0=400 V ; end electrode voltage up to V ̂ =500 V ; and voltage oscillation frequency f 0=1/T=60 kHz .

Experimental investigation of high frequency voltage oscillation in transformer windings

Very fast transient overvoltages (VFTO) comprising oscillating waveforms generate a voltage oscillation in transformer windings. The behaviour of the voltage oscillation in the winding is investigated experimentally on 500 kV class transformers using a pulse and a sinusoidal voltage. The interturn voltages are directly measured using an optical fiber transmission system. In the case of a pulse application, it is found that an interturn traveling wave is generated at either end of the coil and propagates along the winding. In the case of a sinusoidal voltage application, a resonance phenomenon, probably due to the superposition of the traveling waves, is found in the interturn voltage, which could reach 0.25 times the applied voltage. In the tested transformers, the estimated interturn voltage level at incoming VFTO can be 3 times higher than that in the lightning impulse voltage test.

Spin-density-wave sliding: Transient oscillation in high electric field and at low temperature

In (TMTSF) 2AsF 6, we observed transient voltage oscillation under dc pulse current below 3 K. Its amplitude shows an exponential damping. The damping factor is linear function of the voltage oscillation frequency. The ratio of the frequency and the damping factor is constant below 3 K. The origin of the voltage oscillation and of its decay are discussed.

Electrical tuning in hair cells isolated from the chick cochlea

Tall (inner) hair cells were isolated from specific locations in the chick cochlea. The electrical membrane properties of these cells were recorded using the tight-seal whole-cell technique. Depolarizing current steps elicited damped voltage oscillations that ranged in frequency from 100 to 250 Hz among cells from the middle third of the cochlea (basal cells). The current-voltage relation obtained under voltage clamp was dominated by calcium-activated potassium current in the voltage range over which these oscillations occurred. Tall hair cells isolated from the apical tip of the cochlea (apical cells) exhibited action potentials and lower frequency voltage oscillations (5-14 Hz) during depolarizing current steps. Outward currents in these cells were 20-fold slower than those found in the basal cells. These results suggest that electrical tuning of hair cells may play a role in determining the frequency selectivity of the chick cochlea.

Sliding of Charge Density Waves in a Static Electric Field

Some aspects of the motion of charge density waves under a static electric field observed in a number of quasi one-dimensional conductors with an incommensurate superlattice are reviewed. Experiments aimed at the measurement of the CDW phase velocity are described. Recent experiments in the blue bronze Rb0.3MoO3 have shown that the local field oscillation frequency measured by NMR is equal to the periodic voltage oscillation frequency and these both agree with that expected from the measured sliding CDW current.

NMR evidence of the Frohlich mode in Rb 0.30MoO 3

Current-voltage characteristics, voltage oscillations and NMR on the same Rb 0.3MoO 3 crystal at 77 K are presented. The 1 2 , − 1 2 transition at ν 0=80 MHz of 87Rb nuclei broadened by the CDW modulation is motionallu narrowed for bias currents exceeding threshold for non-linear conduction. Calculation of the lineshapes, assuming a partial depinning of the sample, leads to excellent agreement with experiment. An estimate of the ratio of the average current density and voltage oscillation frequency in the depinned region agrees roughly with phenomenological models. A CDW phase correlation time of single domain is deduced to be τ=200 μS.

NMR evidence of the Fröhlich mode in Rb0.30MoO3.

Current-voltage characteristics, voltage oscillations, and NMR on a ${\mathrm{Rb}}_{0.3}$Mo${\mathrm{O}}_{3}$ crystal at 77 K are presented. The \textonehalf{}, - \textonehalf{} transition at ${\ensuremath{\nu}}_{0}=80$ MHz of $^{87}\mathrm{Rb}$ nuclei, broadened by the charge-density-wave modulation, is motionally narrowed for bias currents exceeding threshold for nonlinear conduction. Calculation of the line shapes, on the assumption of a partial depinning of the sample, leads to excellent agreement with experiment. The ratio of average current density to voltage oscillation frequency in the depinned region agrees roughly with phenomenological models. The phase-correlation time of single domains is deduced to be $\ensuremath{\tau}=200$ \ensuremath{\mu}s.

Studies of the discharge mechanisms in electrochemical arc machining

The electrochemical arc machining (ECAM) process combines features of ECM and EDM by application of a pulsed voltage between a cathode-tool and anode-workpiece in a liquid electrolyte. The new process offers rates of metal removal as much as five and fifty times greater than ECM and EDM, respectively. The study reported in this paper explores some of the fundamental processes which occur during ECAM. Experimental apparatus was constructed to enable single pulse discharges to be studied. Results are presented for 200μs pulses between 2 mm diameter silver steel electrodes in NaNO3 and NaCl electrolytes over a gap range of 10 to 90μm. Four stages of electrical phenomena were distinguished within a pulse: (a) high frequency voltage and current oscillations, (b) high rate electrochemical action, (c) low rate electrochemical action, and (d) electrodischarge action. The relative durations of the electrochemical and discharge phases, respectively, increase and decrease with increasing gap width, and vary with electrolyte type and concentration. High speed photography with an image-converter camera was used to record the occurrence of both spark and arc discharge in an electrolyte.