Different characteristics of artificially polluted high voltage composite insulators

Characteristics of leakage current, electrical field and surface resistivity of artificially polluted high voltage composite insulators for different composite materials in their structure, equivalent salt deposit density, electrolyte flow-rate and hydrophobicity are discussed, analyzed and presented in this paper. All these parameters are compared with conventional non composite insulators, too. Relativity of leakage current, applied electric field, electrolyte flow-rate and electrolyte conductivity to the environmental conditions are presented by the results of artificial pollution tests. Waveform, frequency spectrum and magnitude-phase diagram of leakage current of polluted insulators with different pollution densities and durations and applied voltages are presented. Surface resistivity of different insulators is compared regarding different kinds and densities of pollution. Electrical field causing flashover for polluted insulators as a function of the insulators' surface hydrophobicity and salt deposit density is also presented. Through the study, investigating the life time of being used insulators is achieved by measuring their leakage current, salt deposit density and surface resistivity and comparing with the test results

Optimal Capacity of a Battery Energy Storage System based on Solar Variability Index to Smooth out Power Fluctuations in PV-Diesel Microgrids

Battery energy storage systems can be integrated with photovoltaic (PV)-diesel microgrids, as an enabling technology to increase the penetration of PV systems and aid microgrid stability by smoothing out the power fluctuations of the PV systems. The aim of this paper is to derive correlations between the optimal capacity of the smoothing batteries and variabilities in daily solar irradiance. Two commonly used smoothing techniques of moving average and ramp rate control are applied on a real solar irradiance dataset with a 1-minute resolution for a full calendar year across 11 sites in Australia. The paper then presents the developed empirical model, based on linear regressions, to estimate the optimal capacity of the batteries without requiring the use of detailed simulation studies. The performance of the developed technique is validated by numerical simulation studies in MATLAB. The study demonstrates that the empirical model provided reasonably accurate estimates when using the moving average smoothing technique, but had limited accuracy under the ramp rate control technique

Load flow calculation and short circuit fault transients in AC electrified railways

A load flow and short circuit fault simulation of AC electrified railway distribution systems is presented with DIgSILENT PowerFactory software. Load flow of electrified railways distribution system with concerning multi train lines and dynamic characteristics of train load is studied for different time laps. The dynamic characteristics of train load in starting and braking conditions with different starting and stopping times and its moving positions makes the load flow complicated so there is a great need in studying the effects of electrified railways on load flow. Short circuit fault transients is also studied and simulated for both power system or traction distribution system and their effects on the operation of the train sets is investigated

Sensitivity of Electric Vehicles Demand Profile to the Batteries Departure State-of-Charge

This paper focuses on the impacts of considering batteries state-of-charge (SOC) at the departure time on thedemand modeling of plug-in electric vehicles (PEVs). Almost all of the previous researches assumed that PEVs batteries at the departure time are fully charged; however, this assumption is highly questionable because it is probable for a PEV to not be charged every day. The probability density function of a vehicle owners’ willingness to fulfill the daily charging is extracted according to the initial SOC of a PEV and the estimated distance of its next trip. Afterwards, with the aim of considering the uncertainties with the associated random variables as well as properly adjusting vehicles SOC at the departure time, a Monte Carlo based multi loop (MCML) algorithm is developed which is composed of two loops, namely the inner loop and the outer loop. In order to implement the proposed stochastic method, a case study has been conducted employing the gathered datasets related to the ICE vehicles in Tehran. Appropriate Student’s t copula functions have been fitted to the datasets in order to take into account the correlation structure among them as well as to generate the required random samples

Power quality improvement of dispersed generation systems using hybrid filter

A hybrid filter constructed of a shunt active filter and distributed passive filters used for power quality improvement in dispersed generation system is presented. The distribution system consists of two wind turbines using induction generators for producing the required active power and several dynamic nonlinear loads. The power quality problems of dispersed generation LV or MV systems are introduced and the necessity of using hybrid filters instead of active or passive filters alone are discussed. The simulation is done with PSCAD/EMTDC software for a distribution system with dynamic nonlinear loads and wind turbines without any filters, with usage of just shunt active filter or passive filters and the hybrid filter structure, introduced in the paper. Studying and comparing the waveforms, frequency spectrums, harmonic contents and THD of the system current with different filter structures mentioned, proves power quality improvement by the applied hybrid filter

Contributions of Single–Phase Rooftop PVs on Short Circuits Faults in Residential Feeders

Sensitivity analysis results are presented to investigate the presence of single–phase rooftop Photovoltaic Cells (PV) in low voltage residential feeders, during short circuits in the overhead lines. The PV rating and location in the feeder and the fault location are considered as the variables of the sensitivity analysis. The single–phase faults are the main focus of this paper and the PV effect on fault current, current in distribution transformer secondary and the voltage at each bus of the feeder are investigated, during fault. Furthermore, to analyze the bus voltages and fault current in the presence of multiple PVs, each with different rating and location, a stochastic analysis is carried out to investigate the expected probability density function of these parameters, considering the uncertainties of PV rating and location as well as fault location

Application of DSTATCOM for surplus power circulation in MV and LV distribution networks with single-phase distributed energy resources

Single-phase distributed energy resources (DERs), such as rooftop photovoltaic arrays, are usually installed based on the need and affordability of clients without any regard to the power demand of the connected phase of a three-phase system. It might so happen that the power generation in a particular phase is more than its load demand. This may cause a reverse power flow in a particular phase, especially in a three-phase, four-wire distribution system. If now the load demand in the other two phases is more than their respective generations, then these two phases will see a forward power flow, while there will be a reverse power flow in the third phase. This will create severe unbalance in the upstream network. In this paper, a distribution static compensator (DSTATCOM) is used to circulate the excess generation from one phase to the others such that a set of balanced currents flow from or into the upstream network. Two different topologies of DSTATCOM are proposed in this paper for the low and medium voltage feeders. Two different power circulation strategies are developed for this purpose. Furthermore, a suitable feedback scheme is developed for each topology for power converter control. The performance of the proposed topologies and the control schemes for the DSTATCOM is evaluated through computer simulation studies using PSCAD/EMTDC

Improving the Learning Experience of Power System Protection Students using Computer-based Simulations and Practical Experiments

This paper presents a survey on the activities carried out to improve the learning experience of electrical engineering undergraduate students in power system protection unit in Curtin University, Australia. The unit was conducted initially based on lectures and tutorials where only two sessions on computer simulation and one session of laboratory demonstration were conducted. In academic year of 2013, to improve the learningexperience of students, several computer-based simulations and laboratory experiments were prepared. The students are introduced with two power system analysis software, namely ETAP and PSCAD/EMTDC which are used to demonstrate the overcurrent relays performance and their coordination as well as the time transient analysis of different faults in an electric network where some protection relays are applied. A practical setupcomposed of LabVolt electrical modules and SEL relays is used to simulate an electric network. Several tests are built up to simulate fault and protection layout for transformer and induction motor. Finally, a secondary injection test set is used to introduce the concepts of relay testing and commissioning

Distributed Battery Storage Units for Overload Prevention in an Islanded Microgrid

In an islanded microgrid, the load demand must be met by the distrusted generators (DGs) connected to it. Usually this can satisfactorily. However load growth increases, especially the peak load. In such a case, more DGs are to be connected to cater to the load growth. Alternatively if the overloading conditions occur infrequently or remain for shorter periods, storage units can be employed. In this paper, distributed battery storage units (BSUs) are employed for the overloading prevention in an islanded microgrid. It has been assumed that the microgrid only contains inertial DGs and ordinarily they share power in a frequency droop control. When an overloading is detected, the BSUs come on line and share power with the DGs using the same frequency droop control. The detection of overloading condition and when overload has been removed are crucial for this operation. An algorithm is proposed for this purpose. Through simulation studies, it has been demonstrated that the BSUs can be switched on and off seamlessly

Load flow calculation and short circuit faults transients in dispersed generation systems

Load flow and short circuit fault transients of a power distribution system with wind turbines as dispersed generation units is presented. Usage of renewable energies such as wind is already a small part of total installed power system in medium and low voltage networks. In this paper, a radial power distribution system with wind turbines is simulated using DIgSILENT PowerFactory software for their influence on load flow and short circuit fault transients. Short fault occurring in dispersed generation systems causes some problems for the system and costumers such as fault level increase or the problems of sudden fluctuations in the current, voltage, power and torque of the double fed induction machine utilized in the wind turbines which have been studied and investigated