Influence of optical interference and carrier lifetime on the short circuit current density of organic bulk heterojunction solar cells

Based on simple analytical equations, short circuit current density （Jsc） of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important role in the determination of Jsc; and obvious oscillatory behaviour of Jsc was observed as a function of thickness. At the same time, the influence of the carrier lifetime on Jsc also cannot be neglected. When the carrier lifetime is relatively short, Jsc only increases at the initial stage and then decreases rapidly with the increase of active layer thickness. However, for a relatively long carrier lifetime, the exciton dissociation probability must be considered, and Jsc behaves wave-like with the increase of active layer thickness. The validity of this model is confirmed by the experimental results.

Analysis of Short-circuit Characteristics and Calculation of Steady-state Short-circuit Current for DFIG Wind Turbine

Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a significant issue.However,the traditional calculation methods aiming at synchronous generators cannot be directly applied to the DFIG wind turbines.A new method is needed to calculate the short-circuit current required by the planning,protection and control of the power grid.The short-circuit transition of DFIG under symmetrical and asymmetric short-circuit conditions are mathematically deduced,and the short-circuit characteristics of DFIG are analyzed.A new method is proposed to calculate the steady-state short-circuit current of DFIG based on the derived expressions.The time-domain simulations are conducted to verify the accuracy of the proposed method.

Study on Short Circuit Current Calculation of Power System with UHVDC and New Energy Source

With the development of power system, the level of short circuit current will increase accordingly. In general, the influence of the HVDC system and the new energy source is not considered in the calculation of the short circuit current. For the power grid that short circuit current level closes to the interrupting capacity of circuit breaker, it’s necessary to fully consider all kinds of influence factors, careful checking, so as to obtain more accurate calculation results of short circuit current. In 2018, two ±800 kV high-power Ultra High Voltage Direct Current (UHVDC) transmission projects will be connected with Shaanxi power grid, accompanied by a lot of concomitant fossil-fuel generating plants as power resource, and also a large number of new energy source, includes wind power generation and photovoltaic power generation. Around one of the UHVDC converter stations, short circuit current may exceed the withstand limit of some certain circuit breakers. In order to get more accurate short circuit current calculation results, three measures are used: 1) contrastive calculation and analysis by algorithm based on schemes and algorithm based on power flow;2) analysis the influence of UHVDC by electromagnetic transient and electromechanical transient hybrid simulation;3) considered a detailed model of Doubly Fed Induction Generator (DFIG) with low voltage ride through characteristics. The calculation results shows that: in the typical operation mode of Shaanxi power grid of 2018, the original calculation results by conventional calculation method are coincident with the results by considering the influence of algorithms, UHVDC and DFIG in large, in which: the results of the algorithm based on power flow are smaller than that of the algorithm based on schemes about 2 - 8 kA;the steady values of the short circuit current provided by UHVDC converterstation (includes rectifiers and smoothing capacitors) are about 0 - 3 kA;the steady values of the short circuit current provided by DFIG are about 0 - 5 kA. The calculation results can provide reference for the selection of the circuit breaker, and it can be verified by fault recording data in the future.

Calculation of Eddy Current Loss and Short-circuit Force in SSZ11-50000/110 Power Transformer

The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.

Effects of current waveform parameters during droplet transfer on spatter in high speed waveform controlled Short-circuiting GMAW

Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.

Study on Effect of UHV Power Grid Construction Schemes on Short Circuit Current

The commissioning of Southern Hami-Zhengzhou ±800 kV UHVDC transmission project has important significance to heighten operation reliability, transfer capability and supply electric ability of Henan power grid. However, short circuit currents of 500 kV buses in the Center of Henan are almost close to the operation upper limitation. In order to decrease the short circuit currents effectively, it’s necessary to strengthen the network structure of Center of Henan power grid and calculate short circuit currents. Two schemes of strengthening the network structure of Center of Henan power grid are studied. The calculated values of short circuit currents of some important 500 kV buses in the two schemes are still bigger than excepted. According to the latest Plan of State Grid, Yubei UHV substation and Zhumadian UHV substation located in Henan power grid. The calculated values of short circuit currents of some important 500 kV buses with the commissioning of Yubei UHV and Zhumadian UHV are qualified. So, reasonable network structure with UHV is suitable to heighten transfer capability and supply electric ability of Henan power grid.

Short-circuit Current Characteristics of Wind Generators

To study the effects of wind generators on distribution system protection,the short-circuit current(SCC) characteristics of wind generators is important.Although there are many researches on the issue,a clear agreement has not been reached so far.The SCC characteristics for different wind generators are studied.PSCAD simulation is performed in the same system integrated with different kinds of wind generators,and their results are compared with those reported in IEEE papers.The detection possibility by overcurrent relay(OCR)is discussed based on the simulation results.

The simulation research for transient current variation in short circuit fault of urban rail transportation

Urban rail transit is one of the most important way for urban residents. However, frequent power failure, especially the short fault hinders the safe and stable operation of rail transit. The research of the transient variation of line electrical parameters in short circuit fault is the basis of researches for technology of line protection and short circuit fault location. Based on Matlab/Simulink, a 24-pulse rectifier circuit model is established, the resistance and inductance value of the catenary and rail network are calculated. The short Circuit fault simulation model of DC traction power supply system is established. The short-circuit fault of the traction network at close and distant points are simulated, the transient variation values of fault current with the different fault distance are analyzed. The simulation results show that the transient current peak of the nearby short circuit is oscillatory and convergent due to the nonlinear devices, which proves the accuracy of the model and provides a reference for the precise configuration of the line protection equipment.

Research on Numerical Simulation of 3D Leakage Magnetic Field and Short-circuit Impedance of Axial Dual-low-voltage Split-winding Transformer

It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and short-circuit impedance model of axial dual-low-voltage split-winding transformer is established, and then the 2D and 3D leakage magnetic field are analyzed. Secondly, the short-circuit impedance and split parallel branch current distribution in different working conditions are calculated, which is based on field-circuit coupled method. At last, effectiveness and feasibility of the proposed model is verified by comparison between experiment, analysis and simulation. The results showed that the 3D analysis method is a better approach to calculate the short-circuit impedance, since its analytical value is more closer to the experimental value compared with the 2D analysis results, the finite element method calculation error is less than 2%, while the leakage flux method maximum error is 7.2%.

Influence of DFIG Wind Turbine Protection and Control during Voltage Dip on Circuit Breaker Operation

This paper analyzes a DFIG （doubly fed induction generator） WT （wind turbine） fault current after a symmetrical network voltage dip. The goal is to identify the factors determining how fast the first zero crossings of the fault current occur. This is an important subject because the ftmdamental property of the CB （circuit breaker） is that it breaks the current when the current is very near zero. The study was conducted using a hardware-in-the-loop test environment constructed using two real time simulators （dSPACE and RTDS） and a commercial protection relay. It is found that the reactive current injection during a voltage dip demanded by the grid codes enhances the operation of the WT protection because the zero crossings of the currents through CB are attained earlier. In addition, the size of the crowbar resistance has a significant influence on the zero crossings.

Study on the instantaneous protection reliability of low voltage circuit breakers

This paper outlines the significance of enhancing the instantaneous protection reliability of low voltage circuit breakers and describes their main failure modes. The instantaneous failure mechanism of low voltage circuit breakers was analyzed so that measures to improve instantaneous protection reliability can be determined. Furthermore, the theory of the instantaneous characteristics calibration device for low voltage circuit breakers and the method of eliminating the non-periodic component of test current are given in detail. Finally, the test results are presented.

A New Method of Early Short Circuit Detection

To reduce the pressure on contacts and circuit breaker and realize the zone selective interlocking (ZSI) function above the instantaneous protection threshold (e.g., >10In), the short circuit current needs to be early detected. The state-of–art of early short circuit detection (ESCD) method is reviewed. Based on the equivalent model of the short circuit, a new method based on the current and its integration is proposed. The prospective current value can be detected in the early stage of the short circuit. According to the evaluation result, the short circuit current can be early forecasted with the proposed method.

Electrical Performance Study of a Large Area Multicrystalline Silicon Solar Cell Using a Current Shunt and a Micropotentiometer

In this paper, a new technique using a Current Shunt and a Micropotentiometer has been used to study the electrical performance of a large area multicrystalline silicon solar cell at outdoor conditions. The electrical performance is mainly described by measuring both cell short circuit current and open circuit voltage. The measurements of this cell by using multimeters suffer from some problems because the cell has high current intensity with low output voltage. So, the solar cell short circuit current values are obtained by measuring the voltage developed across a known resistance Current Shunt. Samples of the obtained current values are accurately calibrated by using a Micropotentiometer (μpot) thermal element (TE) to validate this new measuring technique. Moreover, the solar cell open circuit voltage has been measured. Besides, the cell output power has been calculated and can be correlated with the measured incident radiation.

Fault Current Identification of DC Traction Feeder Based on Optimized VMD and Sample Entropy

A current identification method based on optimized variational mode decomposition(VMD)and sample entropy(SampEn)is proposed in order to solve the problem that the main protection of the urban rail transit DC feeder cannot distinguish between train charging current and remote short circuit current.This method uses the principle of energy difference to optimize the optimal mode decomposition number k of VMD;the optimal VMD for DC feeder current is decomposed into the intrinsic modal function(IMF)of different frequency bands.The sample entropy algorithm is used to perform feature extraction of each IMF,and then the eigenvalues of the intrinsic modal function of each frequency band of the current signal can be obtained.The recognition feature vector is input into the support vector machine model based on Bayesian hyperparameter optimization for training.After a large number of experimental data are verified,it is found that the optimal VMD_SampEn algorithm to identify the train charging current and remote short circuit current is more accurate than other algorithms.Thus,the algorithm based on optimized VMD_SampEn has certain engineering application value in the fault current identification of the DC traction feeder.

Power supply arm protection scheme of high-speed railway based on wide-area current differential

When fault occurs on cross-coupling autotransformer(AT)power supply traction network,the up-line and down-line feeder circuit breakers in the traction substation trip at the same time without selectivity,which leads to an extended power failure.Based on equivalent circuit and Kirchhoff’s current law,the feeder current characteristic in the substation,AT station and sectioning post when T-R fault,F-R fault,and T-F fault occur are analyzed and their expressions are obtained.When the traction power supply system is equipped with wide-area protection measurement and control system,the feeder protection device in each station collects the feeder currents in other two stations through the wide-area protection channel and a wide-area current differential protection scheme based on the feeder current characteristic is proposed.When a short-circuit fault occurs in the power supply arm,all the feeder protection devices in each station receive the feeder currents with time stamp in other two stations.After data synchronous processing and logic judgment,the fault line of the power supply arm can be identified and isolated quickly.The simulation result based on MATLAB/Simulink shows that the power supply arm protection scheme based on wide-area current differential has good fault discrimination ability under different fault positions,transition resistances,and fault types.The verification of measured data shows that the novel protection scheme will not be affected by the special working conditions of the electrical multiple unit(EMU),and reliability,selectivity,and rapidity of relay protection are all improved.

Heating of the Electrons and the Rectified Current at the Contacts That Are in an Alternating Electromagnetic Field

The paper deals with the heating of electrons and current rectification in contact, which is located in an alternating electromagnetic field. It was found that the electrical component of the microwave (UHF) waves inside the p-n-junction was curved. This leads to the perpendicular component of the electric field of the microwave wave. This component modulates the height of the potential barrier with the frequency of the microwave. In the p-n-junction, straightening microwave current occurs. It is shown that the rectifying contact in the microwave electromagnetic field is always an electromotive force. This is due to carrier heating and straightening microwave current. It is shown that electron heating and straightening of the microwave power will lead to higher ideality factor of the diode.

A Novel Crowbar Impulse Current Circuit for Testing the Switch-Type SPD

A crowbar impulse current circuit for testing the switch-type surge protective device （SPD） is presented. The crowbar circuit consists of a computer control circuit, a trigger voltage pulse generator, a main discharging switch, and a crowbar pseudospark switch. The active trigger technology was studied in the crowbar impulse current circuit. The circuit monitors the main discharging current and generates a trigger signal at a proper time for the crowbar pseudospark switch operation. The trigger characteristics of the main discharge switch and the crowbar pseu- dospark switch were investigated. By monitoring the preset applied capacitor voltage, the gap distance of the main discharging switch could be adjusted to ensure a discharging delay time less than 2 μs. Equipped with a surface ttashover trigger device made of high relative perimittivity dielectric material BaTiO3 （εr = 3460）, the discharge delay time of the crowbar pseudospark switch is less than 85 ns, and the minimum operating voltage is less than 1% of its self-breakdown voltage. With a storage capacitor of 9 μF , an inductor of 18 μH and a crowbar pseudospark switch, a load of 30 mΩ and an applied capacitor voltage of 40 kV, an impulse current waveform of maximum 25 kA was generated with a rise time and time to half peak value of 17.2 μs and 336μs respectively.

Temperature Effects on the Electrical Performance of Large Area Multicrystalline Silicon Solar Cells Using the Current Shunt Measuring Technique

The temperature effects on the electrical performance of a large area multicrystalline silicon solar cell with back-contact technology have been studied in a desert area under ambient conditions using the current shunt measuring technique. Therefore, most of the problems encountered with traditional measuring techniques are avoided. The temperature dependency of the current shunt from 5oC up to 50oC has been investigated. Its temperature coefficient proves to be negligible which means that the temperature dependency of the solar cell is completely independent of the current shunt. The solar module installed in a tilted position at the optimum angle of the location, has been tested in two different seasons (winter and summer). The obtained solar cell short circuit current, open circuit voltage and output power are correlated with the measured incident radiation in both seasons and all results are discussed.

Protection of Low Voltage CIGRE Distribution Network

High quality electricity services are the prime objectives in the modern power systems around the world. One of the main players to achieve this is the protection of the system which needs to be fast, reliable and cost effective. The study about the protection of the Low Voltage (LV) CIGRE distribution grid and networks like this has been proposed in this paper. The main objective of this paper is to develop protection against short circuit faults which might appear anywhere in the network. The protection of the power networks that comprises of renewable energy generation units is complicated because of the bidirectional flow of the current and is a challenge for the protection engineers. The selection of the protection devices in this paper is made to protect the network against faults in grid connected and island mode of operation. Ultra-fast fuses are proposed in order to protect the inverters used for Photovoltaic (PV) and battery applications. The disconnection of the PV solar panels when in island mode is made by proposing switch disconnecting devices. ABB is currently using these kinds of disconnection devices for the purpose of protecting solar panels against over voltages in the case of islanding. The over speed protection of the existing Wind Turbine Generator (WTG) in the CIGRE network in case of grid loss is also proposed in this paper.

Regulating effect of Tong Xie-Yao Fang on colonic epithelial secretion via Cl- and HCO3- channel

AIM To investigate the pharmacological effect of Tong XieYao Fang(TXYF) formula, a Chinese herbal formula, on Diarrhea-predominant irritable bowel syndrome(D-IBS) rats.METHODS In a neonatal maternal separation plus restraint stress(NMS + RS) model of D-IBS, male Sprague Dawley rats were randomly divided into two groups(NMS + RS group and TXYF-formula group) with no handlings were used as controls(NH group). Starting from postnatalday 60, rats in TXYF-formula group were administered TXYF-formula(4.92 g/100 g bodyweight) orally twice a day for 14 consecutive days while NH group and NMS + RS group were given distilled water. Using short-circuit current technology, we observed 5-HT-induced changes of current across ion channels, such as cystic fibrosis transmembrane conductance regulator(CFTR) Clchannel, epithelial Na+ channel(ENaC), Ca2+-dependent Cl- channel(CACC), Na+-K+-2Cl- co-transporter(NKCC), and Na+-HCO-3 co-transporter(NBC), in the colonic epithelium of three groups after exposure to drugs and specific blockers with a Power Lab System(AD Instruments International).RESULTS Under basal conditions, the changes of short-circuit current(?Isc, μA/cm2) induced by 5-HT were similar in NH group and TXYF-formula group, and both higher than NMS + RS group(70.86 μA/cm2 ± 12.32 μA/cm2, 67.67 μA/cm2 ± 11.68 μA/cm2 vs 38.8 μA/cm2 ± 7.25 μA/cm2, P < 0.01, respectively). When CACC was blocked by 4,4′-diisothiocyanato-stilbene-2,2′-disulfonic acid, 5-HT-induced ?Isc was smaller in NMS + RS group than in NH group and TXYF-formula group, respectively(48.41 μA/cm2 ± 13.15 μA/cm2 vs 74.62 μA/cm2 ± 10.73 μA/cm2, 69.22 μA/cm2 ± 11.7 μA/cm2, P < 0.05, respectively). The similar result could be obtained when ENaC was blocked by Amiloride(44.69 μA/cm2 ± 12.58 μA/cm2 vs 62.05 μA/cm2 ± 11.26 μA/cm2, 62.11 μA/cm2 ± 12.01 μA/cm2, P < 0.05, respectively). However, when CFTR Cl- channel was blocked by 1,1-dimethyl piperidinium chloride(DPC), 5-HT-induced ?Isc did not significantly differ in three groups(42.28 μA/cm2 ± 10.61 μA/cm2 vs 51.48 μA/cm2 ± 6.56 μA/cm2 vs 47.75 μA/cm2 ± 7.99 μA/cm2, P > 0.05, respectively). The similar results could also be obtained in three groups when NBC and NKCC were respectively blocked by their blockers.CONCLUSION TXYF-formula can regulate the Cl- and HCO-3 secretion of colonic mucosa via CFTR Cl- channel, Cl-/HCO-3 exchanger, NBC and NKCC co-transporters.