Capacitive Current Measurement Research Articles

Research on signal injection method with high frequency for distribution network capacitive current measurement

The signal injection method to measure capacitive current in the distribution network faces the problems of frequency selection and measuring precision. In this paper, the method of high frequency signal injection is analyzed and improved. The leakage inductance value of voltage transformer (TV) is obtained by injecting 5000 Hz high frequency signals, and the resonance frequency of the grounding capacitance in the distribution network is determined through the sweeping frequency method. The grounding capacitance can be calculated, and the improved series capacitor method is used to reduce the total capacitance of the experimental system, which can accurately measure the capacitance current. Finally, the experiments have been set up and verified to prove the practical feasibility of the proposed method.

The Signal Injection Method with High-Frequency for Distribution Network Capacitive Current Measurement

In order to solve the problem of limited frequency selection range and simplify calculations on the grounded capacitance measurement for the ungrounded distribution system, a high-frequency injecting method for the capacitive current measurement is proposed in the paper. The injecting frequency can be high enough to ignore capacitive reactance and leakage resistance comparing with leakage inductance. The leakage inductance value is obtained directly on the base of simplified calculation. Then the resonant frequency of the power system needs to be obtained by the traditional resonant method. Finally, the grounded capacitance can be calculated through the equivalent circuit and the simultaneous equations. The simulation and experiments verify the feasibility of the high-frequency method. The experiment results prove that this method not only solves the problem of frequency selection, but also has advantages of convenience and high precision (the relative error is less than 5%), which is also suitable for the larger grounded capacitance system.

Investigation of the Dynamic Relaxation Behavior of Biomolecules Immobilized on Metal Electrode in Time Domain

Biomolecules such as DNA immobilized on metal electrodes and non-Faradaic current was measured in buffered solution. The metal-biomolecules-liquid-metal structure can be regarded as a liquid type of capacitor. The measurement of the capacitive current, which is affected by the ions, biomolecules, and liquid in the solutions. It is interesting to investigate the charging and discharging process in time domain, which brings important information of the dynamic behavior of the whole system. In this study, double-stranded DNA (dsDNA) was immobilized on gold electrodes and the capacitive current was measured in buffer solution with a pulse stimulus. Different relation time constants were revealed for various surface modifications. The transient current of the sensor was measured in de-ionized water and in 30 mM TE buffer before dsDNA immobilized metal electrode, and in 30 mM TE buffer after dsDNA immobilized on the metal electrode, followed by different concentrations of HIV-1 RT protein, ranging from 1 aM to 100fM. This technique shows ultra-high sensitivity of the protein detection (1 aM), indicating that this technique is promising for biosensor applications. Figure 1 shows the schematic of device for capacitive current measurements.

Capacitive Current Measurement Methods for Arc-Suppression Coil with Automatic Tuning

Accurately measuring capacitive current for the automatic tuning arc-suppression coil is the premise and basis of its compensating and arc-extinguishing functions. Several principles of capacitive current measurement applied widely are analyzed and compared. The resonance method to measure the capacitive current has high precision, but has complex tuning. The displacement voltage method has simple tuning, but has poor accuracy of measuring capacitive current. The measurement accuracy of the impedance triangle method and the E0 measurement method lies between the resonance method and the displacement voltage method. And its tuning is also relatively simple, but its measurement and control system is more complex. At last, how to choose appropriate capacitive current measurement method according to the arc-suppression coil tuning principle and the distribution network operation is pointed out.

Survey on Capacitive Current Measurement Principles for Automatic Tuning Arc-Suppression Coil

Accurately measuring capacitive current for the automatic tuning arc-suppression coil is the premise and basis of realizing its compensating and arc-extinguishing functions. Several principles measuring capacitive current applied widely are theoretically analyzed and compared. The resonance method to measure the capacitive current has high precision, but has complex tuning. The displacement voltage method has simple tuning, but has poor accuracy of measuring capacitive current. The measurement accuracy of the impedance triangle method and the E0 measurement method lies between the resonance method and displacement voltage method. And its tuning is also relatively simple, but its measurement and control system is more complex. At last, to choose appropriate capacitive current measurement method according to the arc-suppression coil tuning principle and the distribution network operation is pointed out.

Decreased Skeletal Muscle Intramembrane Charge Movement And Contractile Activation In S100A1 Knock Out Mice

S100A1, a calcium binding protein expressed in skeletal and cardiac muscle, modulates Ca2+ signaling. We have previously shown that isolated flexor digitorum brevis (FDB) skeletal muscle fibers from S100A1 knock out (ko) mice exhibit reduced Ca2+ transients with delayed onset in response to single action potentials compared to wild type (wt) FDB fibers (Prosser et al, 2008). Utilizing the potentiometric dye di-8-ANEPPS, we now show no differences in action potential properties between wt and ko fibers. Using whole cell voltage clamp of single isolated fibers we examined surface and transverse tubule membrane electrical properties in wt and ko fibers. Preliminary non-linear capacitive current measurements indicate that maximum charge moved (Qmax) is less in ko than wt fibers (wt Qmax = 43.6 ± 3.4 nC/μF, ko Qmax = 32.0 ± 3.5 nC/μF; p < .05). The temporally delayed, steeply voltage dependent component of intramembrane charge movement at intermediate depolarizations (Qγ) is less pronounced in ko than in wt fibers, consistent with a steeper voltage dependence of charge moved (wt k = 7.2 ± .5, ko k = 10.8 ± 1.2, p < .05). The midpoint voltage of charge moved was not different (wt Vhalf = -26.1 ± 2.8 mV, ko Vhalf = -28.5 ± 1.5 mV). Both the amplitude and the voltage dependence of Cav1 Ca2+ currents were similar in wt and ko fibers. In vivo maximal specific force (force normalized to muscle mass) was significantly decreased in ko compared with wt muscles (wt Po = 1.52 ± .09 g/mg, ko Po = 1.11 ± .09 g/mg; p < .05). These results are consistent with muscles lacking S100A1 having decreased charge moved during membrane depolarization, causing depressed SR Ca2+ release, and ultimately decreased force generation.

Patch-clamp study reveals that the importance of connexin43-mediated gap junctional communication for ovarian folliculogenesis is strain specific in the mouse

Genetic ablation of connexin37 (Cx37) or connexin43 (Cx43), the two gap junction proteins expressed by mouse ovarian granulosa cells, has been shown to result in impaired follicle development. We used patch-clamp techniques to evaluate quantitatively the contribution of these connexins to gap junctional intercellular communication (GJIC) among granulosa cells. The coupling conductance derived from a voltage step-induced capacitive current transient was used as a measure of GJIC in cultured granulosa cells. Using this method, we determined that the conductance of wild-type (84.1 +/- 28.6 nS; n = 6) and Cx37-deficient granulosa cells (83.7 +/- 6.4 nS; n = 11) does not differ significantly (P = 0.35), suggesting a limited contribution, if any, of Cx37 to granulosa cell coupling. In contrast, the conductance between granulosa cells of Cx43-deficient mice (2.6 +/- 0.8 nS; n = 5) was not significantly different from that of single, isolated wild-type granulosa cells (2.5 +/- 0.7 nS, n = 5; P = 0.83), indicating that Cx43-deficient granulosa cells were not electrically coupled. A direct measurement of transjunctional conductance between isolated granulosa cell pairs using a dual patch-clamp technique confirmed this conclusion. Interestingly, a partial rescue of folliculogenesis was observed when the Cx43-null mutation in C57BL/6 mice was crossed into the CD1 strain, and capacitive current measurement demonstrated that this rescue was not due to reestablishment of GJIC. These results demonstrate that folliculogenesis is impaired in the absence of GJIC between granulosa cells, but they also indicate that the severity is dependent on genetic background, a phenomenon that cannot be attributed to the expression of additional connexins.

Complex voltammetric and fractal study of adsorbed layer’s structure of pure Triton-X-100 and in mixture with o- or p-nitrophenol

Adsorption of well-known surfactant Triton-X-100 (T-X-100) and mixed systems comprising T-X-100 with o- or p-nitrophenols, at the mercury/electrolyte solution interface versus T-X-100 bulk concentration has been studied. Diversified approach comprising capacitive current measurements, desorption peak height analysis, fractal analysis, nonthermodynamic calculation of coefficient of lateral interaction, calculation of relative coverage assuming flat and perpendicular dispositions of molecules, fit with Flory–Huggins isotherms corresponding to different molecular orientations, and predictions of random sequential adsorption (RSA) and equilibrium (generalized RSA) theories, together with analysis of reduction mechanisms of nitrophenols has been used. It is found that the adsorbed layer of T-X-100 and mixed layers are fractal. Fine structural changes of adsorbed layer(s) are identified and related to corresponding changes in fractal dimension. Evidence derived from alternating current (ac) and square wave (sw) voltammetric measurements and theoretical considerations support these conclusions. For the adsorption of T-X-100 four different adsorption phases, corresponding to increasing bulk concentration, are identified and characterized. Mixed systems undergo different changes in microstructure that are reflected in observed changes of reduction mechanisms of nitrophenols. Those are in turn related to the differences in molecular interactions between T-X-100 and certain nitrophenol. The results are relevant for study of any system exhibiting fractal features and accessible to electrochemical methods such as adsorbed films, models of biological membranes, etc.

Changes of intrinsic membrane potentials induced by flip-flop of long-chain fatty acids.

The passive transbilayer movement-flip-flop-was investigated on planar bilayer lipid membranes (BLMs), containing myristic, stearic, or linoleic long-chain fatty acids (FA). In response to a transbilayer pH gradient, a difference in the surface charges between inner and outer leaflets appeared. Because the BLM was formed from FA and neutral lipid, a surface potential difference was originated solely by a concentration difference of the initially equally distributed ionized FA. As revealed by zeta-potential measurements, the corresponding surface potential difference DeltaPhi(s) was at least twice the value expected from a titration of the FA alone. The additional surface charge was attributed to FA flip-flop induced by the transbilayer pH gradient. DeltaPhi(s) was derived from capacitive current measurements carried out with a direct current (dc) bias and was corrected for changes of membrane dipole potential Phi(d). Dual-wavelength ratiometric fluorescence measurements have shown that Phi(d) values of the pure DPhPC bilayers and BLMs containing 40 mol % FA differ by less than 6%. It is concluded that fast FA flip-flop is not restricted to membranes with high curvature. The role of pH gradient as an effective driving force for the regulation of FA uptake is discussed.

Changes of the membrane potential profile induced by verapamil and propranolol

The effects of the organic calcium channel blocker verapamil and the β-receptor blocker propranolol on dipole (φd) and surface (φs) potentials of bilayer lipid membranes were studied. The boundary potentials (φb=φd+φs) of black lipid membranes, monitored by conductance measurements in the presence of nonactin and by capacitive current measurements were compared with φs calculated from the electrophoretic mobility of lipid vesicles. It was shown that the increase of boundary potential, induced by the adsorption of the positively charged propranolol, was caused solely by an increase in surface potential. Although φs also increases due to the adsorption of verapamil, φb diminishes. A sharp decrease of the dipole potential was shown to be responsible for this effect. From Langmuir adsorption isotherm the dissociation constant Kd of verapamil was estimated. The uncharged form of verapamil (Kd=(0.061±0.01) mM at pH 10.5) has a tenfold higher affinity to a neutral bilayer membrane than the positively charged form. The alteration of membrane dipole potential due to verapamil adsorption may have important implications for both membrane translocation and partitioning of small or hydrophobic ions and charged groups of membrane proteins.

Permeation of phloretin across bilayer lipid membranes monitored by dipole potential and microelectrode measurements

The transmembrane diffusion of phloretin across planar bilayer lipid membranes is studied under steady-state conditions. Diffusion restrictions and adsorption related effects are measured independently. The adsorption of aligned phloretin dipoles generates a change in the intrinsic dipole potential difference between the inner and outer leaflets of the lipid bilayer. It is monitored by capacitive current measurements carried out with a direct current (dc) bias. The variation of the intramembrane electric field indicates a saturation of the binding sites at the membrane interface. In contrast, pH profile measurements undertaken in the immediate membrane vicinity show a constant membrane permeability. If phloretin binding and transmembrane diffusion are treated as two competitive events rather than subsequent steps in the transport queue the contradictory results become explainable. A mathematical model is developed where it is assumed that diffusing phloretin molecules are randomly oriented, i.e., that they do not contribute to the intrinsic membrane potential. Only the dipoles adsorbing onto the membrane are oriented. Based on these theory the membrane permeability is calculated from the capacitive current data. It is found to agree very well with the permeability deduced from the microelectrode measurements.