Volume 19, Issue 1 -

This paper describes the use of conventional and unconventional partial discharge tests by capacitive and inductive coupling in Instrument Transformers (IT). The objective of this work was to evaluate Phase-Resolveld Partial Discharge (PRPD) signatures features obtained during on-site (online) and laboratory (offline) measurements, by comparing results with state-of-the-art patterns and standard recommendations. The analysis of the results showed that is possible to obtain partial discharge (PD) patterns - corona, background noise, internal PD, free potential and surface PD - at on-site measurements but those are compromised by the pulse attenuation, difficulties in performing measuring system calibration and the absence of reference voltage. Suitable range of on-site measuring was above 1 MHz up to 5 MHz. The results reached in on-site measuring can be used as image preprocessing methodology to perform automatic pattern recognition of partial discharge signature. It is also described the parameterization of the HFCT for different frequency filter values though carrying out HFCT parameterization for different types of high voltage equipment was not objective of this work.

This paper proposes a decoupled AC/DC power flow approach for multi-terminal HVDC systems. The proposed method simplifies the power flow computation of multi-terminal HVDC systems while accurately reflecting the operation and control characteristics of VSC (voltage source converter) stations in a HVDC network. In the DC network, the power flow calculation is conducted based on a slack DC bus VSC station and power commends issued to other VSC stations from the power system control center. Then, in the AC power flow calculation, VSC stations are treated as special AC generators that can generate and absorb power from the AC grid in active and reactive power or active power and bus voltage control mode. For validation purpose, the conventional unified power flow method for multi-terminal HVDC systems is built. The paper compares the proposed method with the unified power flow method for an 8-bus multi-terminal HVDC system based on MATPOWER. Then, more case studies for different VSC control modes are conducted and evaluated for the 8-bus system. Afterwards, the proposed method is applied to the power flow study of a more practical and complicated multi-terminal HVDC system based on the IEEE 118-bus system.

In electric power systems, not all fault conditions remain unchanged during faults. An evolving fault has one characteristic initially and changes to a different condition subsequently. Locating evolving faults is challenging due to the change in fault type shortly after the fault initiation. This paper presents a new approach for estimating the locations of evolving faults on transmission lines. By using sparse wide area voltage measurements, this method is able to accurately locate evolving faults without requiring measurements from either end of the faulted line. There is no need to detect whether a fault is an evolving fault or not. Fault type information is not a necessity either, and the change of fault phases does not affect the estimation accuracy. In addition, the algorithm is applicable to both single-circuit and double-circuit lines, and the transmission lines can be either transposed or untransposed. Distributed parameter line model is adopted to fully consider the shunt capacitances of the transmission lines. Electromagnetic Transient Program (EMTP) is employed to simulate transmission system, and quite accurate results have been achieved.

In this study, the wind energy potential and the unit energy cost related to six wind turbines in the city of Illizi in Southeast of Algeria are investigated. The hourly measured data (wind, pressure and temperature) observed during the period 2005–2014 at meteorological station in Illizi were used. An analysis of the collected data using the Weibull statistical method was made. The preliminary results were used to evaluate the power density in this region. Moreover, technical data of six chosen wind turbine models were analyzed to select the best appropriate turbine according to the techno economic analysis. The annual energy output of the selected wind turbines was calculated and the energy cost for each model was evaluated using two different methods. Input parameters affecting the cost, return on investment and payback period are also studied. For the 1MW wind turbine which, according to the economic analysis, is found to be the most suitable for this region, the cost of energy per kWh varies between 0.0388$ and 0.0634$ with PVC method and in range of 0.0878$ to 0.1142$ with LCOE method.

This paper presents a comparative assessment of two controllers, namely sliding mode controller and hysteresis controller for active power filtering of a grid integrated Photovoltaic (PV) system. These control algorithms were employed in Voltage Source Inverter (VSI) for active power filtering as well as for converting the dc voltage from PV array to 3-phase ac voltage. For superior tracking efficiency a modified Incremental Conductance Maximum Power Point Tracking (ICMPPT) algorithm is employed to extract maximum power from PV panels. A PI controller is used for regulation of dc link capacitor voltage. Instantaneous power theory based reference current generation is used for the active power filtering. Both sliding mode control algorithm and hysteresis control algorithm are designed for tracking the reference inverter current in order to elimination the grid current harmonics. The steady state and transient performances of the two controllers i. e. sliding mode controller and hysteresis controller are compared. These two control schemes are implemented on a grid connected PV system firstly using MATLAB/Simulink and then on an experimental setup developed in the laboratory. From the obtained simulation and experimental results, it is found that sliding mode controller exhibits superior performance such as better transient and steady state behavior under parameter uncertainties as compared to the hysteresis controller.

An electrical network constantly faces unforeseen events such as faults on lines, loss of generation, etc. Under Frequency Load Shedding (UFLS) and Generator Tripping are traditional methods used to stabilise a network when a transient fault occurs. These methods will prevent any network instability by shedding load or tripping the most critical generator at a calcultated time when required. By executing these methods, the network can be stabilised in terms of balancing the generation and the load of a power system. A hybrid control scheme is proposed where the traditional methods are combined to reduce the stress levels exerted on the network and to minimize the load to be shed.

The mechanical performance of permanent magnet brushless DC motor (BLDCM) servo system is affected by the moment of inertia. In order to obtain the load moment of inertia effect on the motor dynamic performance, based on the time stepping finite element method (FEM), a two-dimensional finite element model of the BLDCM is established, and the motor drive circuit is built. The motor running state under different load moment of inertia is simulated. The motor dynamic characteristics and the output performance are studied. The influence of the moment of inertia on the starting characteristics and the load sudden change characteristics is obtained. The influence mechanism of the load moment of inertia on the motor output speed and torque is revealed. Finally, a prototype platform is built to test the motor no-load EMF. The correctness of the model is verified and the correctness of the research is proved indirectly. This research is of great significance to the research of the BLDCM servo control system.

This paper aims to conduct the risk assessment of transmission network based on the search of cascading failure chains. Regarding the generalized cascading failure model with transient stability constraints, some significant improvements including the subsequent failure search strategy and the system control measures are proposed during analysis. Besides, the risk evaluation indices pertinent to the failure chains combined with the actual engineering requirements, and the failure level classification are elaborately derived and discussed. Finally, case studies are performed on a real-sized Chinese power grid to illustrate the validity of the proposed strategies and methods.

The monitoring of power quality is a central topic for both household electrical and industrial equipment. Typically, the lacks of quality in a power system (both a public mains and an industrial power supply network) involve interruptions and deviations of the actual supply signals from the nominal characteristics, with potential annoying effects in electrical power systems and problems in industrial and communication apparatus. In this paper, the design and implementation of a measuring system based on a high-performance microcontroller that carries out the power quality analysis of the mains is presented. The system measures the fundamental parameters related to the system under monitoring, that can be a single or a three phase network. The proposed measurement instrument is mainly based on the Microchip PIC32MZ2048ECH100 Digital Signal Controller (DSC) and the Texas Instruments ADS8558 A/D converters (ADCs). Starting from voltage and current sampled values, simultaneously acquired by the converters, the DSC calculates the following parameters: frequency; RMS voltage; RMS current; phase shift; active power; reactive power; apparent power; THD. The measured parameters are also externally transmitted via a serial link. In the paper a prototype of the proposed instrument is described. It is linked to a PC and results shown on a LabVIEW based user interface, reporting also results from lab tests during the metrological characterization phase. Its main features (cost effectiveness, reduced dimensions and low power consumption) make it suitable for installation into existing electric cabinet of civil and commercial users. The continuous and real-time monitoring capability, managed both locally or remotely, is one of the most interesting features.

This paper proposes a novel shunt capacitor (SC) based voltage stability method for a power system operation. The integration of distributed generators e.g. wind and PV powers to the grid, and fluctuations nature of load power cause the attention of voltage stability management for a power system operation and planning. The SC based proposed method improves the voltage stability by using the flow of active and reactive powers in the transmission line. The Voltagestability index (VSI) is utilized for the voltage stability analysis. The SC is installed at the load bus so that it can inject a proper amount of reactive power for ensuring the voltage stability of power system. The proposed method is investigated in the IEEE-14 bus test system. Simulation results are compared with the non-SC based method. Extensive simulation analyses have been done by the MATLAB/Simulink software.

The reduction of power of the autonomous microgrid is proposed in this paper. The concept utilized is Conservative Voltage Reduction (CVR). The active and reactive power consumption of the microgrid decreases and a power reserve of the system increased. The voltage–current droop mechanism is used to lessen the voltage of the DG and it reduces the consumption of power on the consumer side. This reduced power is used to cater more demands. The control strategy is used to cater the greater number of loads at the time of power shortage. The DG taken in this paper is photovoltaic (PV) system and perturb & observe MPPT is used. The interleaved boost converter is used as DC- DC converter as it lessens the ripple of the output voltage and inputs current. The simulation is done on MATLAB platform and results are validated at different loading conditions and comparison has been done with P-f/Q-V mechanism.

Abstract — A mathematical model of a multi-phase power conversion system composed of modified bridge-elements (B-system) capable for parallel computation has been developed. Experimental validation on the example of a power system including a synchronous generator and an AC-DC rectifier has been performed. A mathematical algorithm for B-system assembly and steps to obtain mathematical model of the B-system have been developed. Integration of mathematical models of conversion system into the complete model of a multi-phase power system has been explained and evaluation of computational efficiency of parallel computation techniques for the developed model of an AC-DC-AC converter has been performed. The presented modelling method can be employed in the design phase of smart grids, for power quality and conducted emission analysis.