Component Of Short-circuit Current Research Articles

Practical calculation of asymmetric short circuit current of DFIG connected to distribution network

In view of the existing complex analytic calculations of DFIG short-circuit current are hardly applied in engineering projects, a practical calculation of asymmetric short-circuit current of DFIG is proposed. According to the complex sequence and their Thevenin equivalent model of DFIG network, the composition of each sequence component of DFIG short-circuit current is analysed. Moreover, considering the low-voltage ride through strategy of DFIG, the negative sequence periodic components of short circuit current are well analysed during the crowbar activation and deactivation, and the formula of the negative sequence periodic components of short circuit current are derived. On the basis of positive and negative sequence open circuit voltage, calculating impedance and rotor current, the judgement of crowbar activation is established. The pre-calculated surfaces of negative sequence periodic components of short circuit current are proposed, and the procedure for calculating the asymmetric short-circuit current of DFIG is designed. Finally, the proposed method is verified by simulation.

An adaptive directional current protection scheme for distribution network with DG integration based on fault steady-state component

In view of the low reliability of traditional protection in the distribution network caused by the massive integration of DGs (distributed generation), an adaptive directional current protection scheme based on fault steady-state component is proposed in this paper. First, by analyzing the fault transient characteristics and fault equalization methods of different types of DGs, the components of system short circuit current are calculated, and the relationship between three phase components of the short circuit current is revealed. On this basis, according to the fault boundary conditions, the fault steady-state components are obtained. And then, combined with the measured voltage and measured current at the relaying point, the equivalent voltage and equivalent impedance at the backside of protection are calculated. Thus the adaptive directional current protection criteria for different fault types are formed. Simulation results demonstrate that, the proposed scheme is not affected by the type and power output of DG and the system operation mode, and could effectively prevent the protection from refusing to operate due to voltage drop.

Influence of Third Harmonic Back EMF on Modeling and Remediation of Winding Short Circuit in a Multiphase PM Machine With FSCWs

For multiphase open-winding permanent-magnet (PM) machines, both back electromotive force (EMF) and short-circuit current (SCC) contain third harmonic components that interact with each other and produce even-harmonic torque pulsation. This paper investigates the impact of the third harmonic component on SCC prediction, torque pulsation and postfault remediation method in case of a winding short-circuit fault. Analytical modeling of SCC is developed, which shows that the third harmonic SCC increases the maximum value of SCC. It is found that the transient SCC is heavily influenced by the initial phase angle of winding axis and exciting current when the fault is incepted. The braking torque due to the negative q -axis SCC component is investigated, which peaks at low speed as winding inductive impedance goes down. The comparison of two postfault remediation methods for single-phase short-circuit faults shows the importance of considering the third harmonics of SCC and back EMF in terms of torque performance. Finally, the theoretical results of SCC, braking torque, and remediation methods are verified and evaluated with experimental results.

Estimation of protection's criterion values during arc distortion

Arc distortion can lead to the measuring signal deformation and, consequently, to the erroneous identification or localisation of the fault. In the paper, a study on the short circuit loop resistance and reactance is presented referring to the algorithms using correlation between the sine and cosine functions as well as the least-square method (LSM). In the study, both the static and the dynamic models of the short circuit arc have been employed. The very advantageous features of the LSM-based algorithm have been underlined regarding accuracy of estimation of the short circuit mesh parameters (including the arc voltage at the location where the fault occurs) as well as susceptibility to the presence of a non-periodic short circuit current component.

Antikaliuretic action of trimethoprim is minimized by raising urine pH

This study was designed to test the hypothesis that the antikaliuresis caused by trimethoprim could be diminished by alkalinizing the luminal fluid in the CCD, thereby converting trimethoprim from its cationic, active form to an electroneutral, inactive, form. Trimethoprim-induced inhibition of transepithelial Na+ transport was examined in A6 distal nephron cells by analysis of short circuit current. The voltage-dependence of the trimethoprim-induced block of Na+ channels was examined with patch clamp recordings of A6 cells. The antikaliuretic effect of trimethoprim was examined in vivo in rats pretreated with deoxycorticosterone and with NH4Cl to lower urine pH, and in rats also receiving acetazolamide to raise urine pH. We found that the concentration of trimethoprim required to inhibit the amiloride sensitive component of short circuit current by 50% (IC50) was 340 microM (at pH 8.2) and 50 microM (at pH 6.3). The IC50S of protonated trimethoprim were similar (34 microM at pH 8.2 and 45 microM at pH 6.3). The mean time open for the high selectivity, Na+ channel was reduced from 1679 +/- 387 msec to 502 +/- 98 msec with addition of 10-5 M trimethoprim to patch pipette solution at the resting membrane potential (-Vpipette = 0 mV). further decreases in mean time open were observed as -Vpipette was reduced (that is, apical membrane hyperpolarization) to -40 mV (mean time open = 217 +/- 85 msec) and to -80 mV (mean time open = 69 +/- 13 msec). In vivo, trimethoprim caused a > 50% reduction in potassium (K+) excretion due primarily to a fall in the [K+] in the lumen of the terminal CCD. This effect of trimethoprim was markedly attenuated in an alkaline urine induced by acetazolamide. We conclude that it is the charged, protonated species of trimethoprim which blocks epithelial Na+ channels. Increasing urinary pH decreases the concentration of the charged species of trimethoprim and minimizes its antikaliuretic effect.

Linear Couplers, Field Tests and Experience at York and Middletown Pa.

THE system of bus protection using linear couplers, or air-core mutual reactors, in place of current transformers was described before the Institute in January 1942.1 By special design the mutual reactors were made astatic or insensitive to outside fields. Through the use of air core the troublesome problem of saturation of iron by the d-c transient component of short-circuit current was eliminated. At the same time adequate energy was derived for decisive relay operation. The coupler secondaries were connected in a series loop including the relay to form a bus protective system.