Doaa Khalil Ibrahim

Interconnected transmission systems are increasingly spreading out in HV networks to enhance system efficiency, decrease reserve capacity, and improve service reliability. However, the protection of multi-terminal lines against Broken Conductor Fault (BCF) imposes significant difficulties in such networks as the conventional distance relays cannot detect BCF, as the BCF is not associated with a significant increase in current or reduction in voltage. Traditionally, the earth fault relays in transmission lines may detect such fault; Nonetheless, it suffers from a long delay time. Moreover, many of the nearby earth fault relays detect the BCF causing unnecessary trips and badly affecting the system stability. In this article, a novel single-end scheme based on extracting transient features from current signals by discrete wavelet transform (DWT) is proposed for detecting BCFs in interconnected HV transmission systems. The suggested scheme unit (SSU) is capable of accurately detecting all types of BCFs and shunt high impedance faults (SHIFs). It also adaptively calculates the applied threshold values. The accurate selectivity in multi-terminal lines is achieved based on a fault directional element by analyzing transient power polarity. The SSU discriminates between internal/external faults effectively utilizing the time difference observed between the first spikes of aerial and ground modes in the current signals. Different fault scenarios have been simulated on the IEEE 9-Bus, 230 kV interconnected system. The achieved results confirm the effectiveness, robustness, and reliability of SSU in detecting correctly BCFs as well as the SHIFs within only 24.5 ms. The SSU has confirmed its capability to be implemented in interconnected systems without any requirement for communication or synchronization between the SSU installed in multi-terminal lines.

Integration of Distributed Generation (DG) on the power system networks causes several difficulties, especially for the system protection. One of the important problems associated with system protection is the islanding that takes place when a DG unit (or group of units) continues to energize a part of the load separated from the main utility. As a result, many obstacles occur such as voltage and frequency fluctuation, in addition to personnel safety problems during maintenance. In this paper, the islanding problem is discussed and also the previous islanding detection techniques are investigated to get an efficient technique for islanding detection. The proposed technique is based on estimating the Rate of Change of Zero Sequence of Second Harmonic Voltage at the Point of Common Coupling (PCC). The proposed technique is extensively tested for inverter-based DG includes wind turbines with double-fed induction generator (DFIG). The proposed technique could distinguish the islanding operation correctly within only one cycle without non-detection zone (NDZ). In addition, it could differentiate between the islanding operation at different values for active and reactive power mismatch. Several scenarios are tested such as normal load variation, capacitor switching and power quality disturbances like voltage sags and swells. Faults and outage of one of DGs are also tested.

This paper investigates the impacts of the centralized and distributed grid-connected photovoltaic systems on radial distribution networks. Different weather conditions are considered. Different PV penetration levels are investigated in both centralized and distributed PV configurations. Daily simulation is performed using the Open Distribution System Simulator (OpenDSS). The study will include the impacts on voltage magnitude, the voltage regulators, the voltage unbalance factor and losses during the day. The simulations results are presented in details and conclusions are drawn based on them.

Airports can play a major role in reducing the burden on the national electric grid as they have several factors that make them optimum models for applying energy efficiency strategies. Accordingly, this paper presents a Dual-Dimension Strategy (DDS) to improve the energy efficiency in the airports. This strategy aims to study the opportunities of improving energy efficiency in a way that do not affect the comfort level of occupants, as well as studying the challenges of implementing PV power stations at or around the airports without affecting the safety of aviation. In this context, a case study was conducted at Sharm-Elshiekh airport as a high occupancy level airport to discuss the opportunities and challenges accompanied by the proposed strategy. The detailed simulation of the proposed strategy was carried out using the “DesignBuilder” software, which is automatically conducted with the “EnergyPlus” simulator. Results showed that airports have an opportunity to reduce its energy consumption by up to 25% monthly by using smart control systems such proposed fuzzy system. In addition, the implementation of PV stations in or round the airports can contribute in feeding the airports with a huge amount of clean energy according to the available space and the irradiation in the site of the airport. All of these results refer to save millions of carbon emissions which resulted from depending on fuel sources.

Discrimination and location of faults in Flexible Alternating Current Transmission Systems (FACTS) have several challenges in power systems. This is because of the errors in the measured impedance due to FACTS control actions. The presence of series FACTS in a transmission line complicates both the fault location and discrimination between faults behind and in front of the FACTS device. This paper proposes an integrated solution for both fault zone discrimination (either in front of or behind the FACTS device) and fault location for series FACTS-compensated transmission lines. Online calculations are carried out to estimate the percentage of compensation. After fault inception, a wavelet-based algorithm is used to decide whether the fault is in front of the FACTS device or behind it. Then, a conventional distance protection algorithm is used to estimate the fault zone. After that, synchronized data signals from both ends are used to locate the exact location offline. The algorithm is tested using a real data for a 380 kV, 400 km series-compensated line in Saudi Arabia using MATLAB/SIMULINK. Different types of faults are applied to validate the effectiveness of the algorithm. Metal-Oxide Varistor (MOV) nonlinearity is also considered. Simulation results show the effectiveness of the algorithm.

To ensure high reliability of the power system, distance relays are blocked during power swings. However, if a fault occurs during a power swing, it should be detected and the unblocking function should be invoked to clear the fault as soon as possible. Distinguishing stable and unstable power swing is one of the challenging tasks for distance relays. This paper proposes a combined scheme for detectingfaults occurrence during power swings and accurate determination of power swing stability status. The proposed scheme utilizes a differential power-based technique and a negative sequence current based technique for detecting faults occurrence during power swings. Moreover a wavelet based power angle criteria based algorithm is applied for distinguishing stable and unstable power swings. The proposed scheme is extensively tested for symmetrical and unsymmetrical faults during slow and fast power swings for simulated tested power systems using ATP software.

This paper presents a new adaptive tripping time scheme which provides high speed distance relay operation under fault conditions near the relay point and provides high secured detection for the faults occurred at the end of the protected transmission line with tripping time less than one power cycle. The proposed scheme automatically controls the data window length to adaptively speed up its response under various fault conditions. The advanced feature of this scheme provides capability for fast tripping decisions with secure operation. The proposed scheme possesses the advantage of removing decaying DC offset component in the current signals according to the length of data window, and compensates the capacitive current during the calculation of the fault impedance. Extensive simulations show that the proposed scheme provides better protection performance compared with the conventional schemes of the fixed data window.

Power swings, both stable and unstable, may precipitate wide spread outages to power systems with the result that cascade tripping of the power system elements occur. This paper deals with improving Mho and Quadrilateral relays performance under power swing conditions by discriminating between faults and power swings phenomenon. Distance relay may misinterpreted power swing as three-phase fault, but wavelet transform is able to discriminate clearly between power swings and faults. So, a logic block for fault detection based on the wavelet transform combined with the output of the conventional distance relay is proposed. Only voltage signals are used in wavelet relay to distinguish between fault and power swings conditions. The described scheme has been tested on a double line simulated power system using MatLab program.

Adaptive SPAR offers many advantages over conventional techniques. In the case of transient faults, the arcing extinction time can be accurately determined and in the case of a permanent fault, breaker reclosure can be avoided. This paper describes, in some detail, the design of a new Adaptive SPAR technique that extracts high frequencies transients, from the CVT. The main case of study in this paper is the High Dam / Nagh Hamady, Nagh Hamady /Assuit 500 kV double circuit transmission system in the Egyptian network. Fault scenario cases representing different fault locations, inception angles, actual representation to secondary arc characteristics, and with/without shunt reactor existence were extracted from simulation work, and then verified through real field records in that system. The outcome of this study indicates that the proposed technique can be used as an effective means of achieving an adaptive single pole auto reclosure scheme.