Mohamed A. Izzularab

Modeling and experimental verification of high impedance arcing fault in medium voltage networks

A high impedance arcing fault due to a leaning tree in medium voltage (MV) networks is modeled and experimentally verified. The fault is represented in two parts; an arc model and a high resistance. The arc is generated by a leaning tree towards the network conductor and the tree resistance limits the fault current. The arcing element is dynamically simulated using thermal equations. The arc model parameters and resistance values are determined using the experimental results. The fault behavior is simulated by the ATP/EMTP program, in which the arc model is realized using the universal arc representation. The experimental results have validated the system transient model. Discrete wavelet transform is used to extract the fault features and therefore localize the fault events. It is found that arc reignitions enhance fault detection when discrete wavelet transform is utilized

DWT-Based Detection and Transient Power Direction-Based Location of High-Impedance Faults Due to Leaning Trees in Unearthed MV Networks

Electrical faults due to leaning trees are common in Nordic countries. This fault type has been studied in and it was found that the initial transients in the electrical network due to the associated arc reignitions are behavioral traits. In this paper, these features are extracted using the discrete wavelet transform (DWT) to localize this fault event. Wireless sensors are considered for processing the DWTs on a residual voltage of different measuring nodes that are distributed in the network. Therefore, the fault detection is confirmed by numerous DWT processors over a wide area of the network. The detection security is also enhanced because the DWT responded to a periodicity of the initial transients. The term for locating the faulty section is based on the polarity of a specific frequency bandpower computed by multiplying the DWT detail coefficient of the residual current and voltage at each measuring node. The fault due to a leaning tree occurring at different locations in an unearthed 20-kV network is simulated by the alternate transients program/electromagnetic transients program and the arc model is implemented using the universal arc representation. Test cases provide evidence of the efficacy of the proposed technique.

Modeling and Experimental Verification of a High Impedance Arcing Fault in MV Networks

In this paper, a high impedance arcing fault of the tree leaning type in medium voltage (MV) networks is modeled and experimentally verified. The fault is represented as two parts; an arc model and a high resistance. The arc is generated by the tree leaning towards the network conductor and the tree resistance limits the fault current. The arcing element is dynamically simulated using thermal equations. The arc model parameters and resistance values are determined using the experimental results. The fault behavior is simulated by the ATP/EMTP program, in which the arc model is realized using the universal arc representation. The experimental results have validated the system transient model. Discrete wavelet transform (DWT) is used to extract the fault features and therefore localize the fault events. It is found that arc restrikings enhance fault detection when DWT is utilized

The role of interfacial zone in dielectric properties of transformer oil-based nanofluids

Transformer oil-based nanofluids have unexpected and distinctive dielectric properties that are different from properties of constituting components. This is believed to be attributed to the effect of interfacial zone between oil and nanoparticles. Accordingly, this paper aims to investigate the role through which the interfacial zone affects the dielectric properties of transformer oil-based nanofluids. Oil-based nanofluids are prepared with two different types of nanoparticles having different surface charging polarity. These types are alumina (Al2O3) nanoparticles with cationic surface and titania (TiO2) nanoparticles with anionic surface. For each type of nanoparticles, two groups are prepared with and without a surface modifier, which is called surfactant. Each group consists of four samples having nanoparticles weight fractions of 0.01, 0.04, 0.07 and 0.1 g/L. Surfactant is chosen with charge opposite to that of nanoparticle surface charge to be adsorbed on the nanoparticle surface. For each nanofluid sample, surfactant is distributed through the oil using magnetic stirrer, and then, nanoparticles are mixed and homogenized using magnetic stirrer and ultrasonic processing. After preparation, dielectric properties including breakdown strength and dielectric constant are measured. Based on the obtained results, the role of interfacial zone could be clarified in conjunction to that developed in solid nanodielectrics.

DWT-Based Investigation of phase currents for Detecting High Impedance Faults Due to Leaning Trees in Unearthed MV Networks

In this paper, features of earth faults due to leaning trees are extracted from the network phase currents using the discrete wavelet transform (DWT). Due to the associated arc reignitions, the initial transients in the electrical network give behavioral traits. The detection security is also enhanced because the DWT is responded to a periodicity of the initial transients. The absolute sum of the DWT detail d3 coefficient corresponding to the frequency band 12.5-6.25 kHz is computed over one power cycle for each phase current of each feeder where the sampling frequency is 100 kHz. It is found that the faulty phase has the highest absolute sum when it is compared with the other healthy phases. Similarly, the absolute sum of the faulty feeder is the highest when the comparison is carried out with respect to other feeders. Therefore, two logic functions are suggested to determine the faulty phase and the faulty feeder. The fault due to a leaning tree occurring at different locations in an unearthed 20 kV network is simulated by ATP/EMTP and the arc model is implemented using the universal arc representation.

Feature Extraction of High Impedance Arcing Faults in Compensated MV Networks. Part I: DWT-Based Analysis of Phase Quantities

In this paper, the initial transients in the electrical network due to arc reignitions associated with high impedance faults caused by leaning trees are extracted from phase voltages and currents. The discrete wavelet transform (DWT) is used for the fault feature extraction corresponding to band frequency 12.5- 6.25 kHz and therefore localizing this fault occurrence. The detection security is enhanced because the DWT is responded to a periodicity of the initial transients. A novel technique for the selectivity term of the faulty feeder is introduced. It is based on the power polarity, in which, this power is computed by multiplying the DWT detail coefficient of the current and voltage for each feeder. The fault due to a leaning tree occurring at different locations in an unearthed 20 kV network is simulated by ATP/EMTP and the arc model is implemented using the universal arc representation.

Feature Extraction of High Impedance Arcing Faults in Compensated MV Networks. Part II: DWT-Based Analysis of Residual Components

Electrical faults due to leaning trees have been studied in [1]-[2] and it was found that the initial transients due to the associated arc reignitions are behavioral traits. These transients have been localized using the discrete wavelet transform (DWT). In this paper, these features are extracted from residual voltages using DWT. Therefore, the fault localization is carried out. The term for locating the faulty feeder is based on the polarity of a specific frequency band-power computed by multiplying the DWT detail coefficient of the residual voltage and current for each feeder. The performance of the proposed technique is getting better when the residual waveforms are utilized. Test cases provide evidence of the efficacy of the proposed technique.

Operation evaluation of DWT-based earth fault detection in unearthed MV networks

A novel selectivity technique to estimate the faulty feeder in MV networks was introduced in [1]. This technique depended on the directionality of discrete wavelet transform (DWT) detail coefficient of a residual current of each feeder with respect to the DWT detail coefficient of the residual voltage. The algorithm efficacy has been examined with high impedance arcing fault due to leaning trees. In this paper, the algorithm performance is tested with resistance earth faults over a wide range of the fault resistance values (1 mOmega to 100 kOmega) as well as concerning practical fault cases such as arcing faults. The fault cases occurring at different locations in an unearthed 20 kV network are simulated by ATP/EMTP. Test cases confirm the efficacy of the proposed technique.

Salient features of autotransformer overvoltages caused by ferroresonance and load rejection

This paper deals with overvoltages due to cable and autotransformer interaction either ferroresonance or load rejection. The studied ferroresonance overvoltages are due to single-phase switching in the source feeding an unloaded transformer via a power cable. While the other overvoltages are caused by load disconnection from the cable that connects between the autotransformer and load. Both overvoltage cases are studied with 250 MVA, 400/132/18 kV, three-winding autotransformer. The simulation is carried out using Alternative Transients Program (ATP). An evaluation for the impact of the transformer grounding concept on the resulted overvoltage features is presented for both cases. Also, the effect of cable length on the overvoltage behavior is studied for the two situations and the ferroresonance mode is defined. Ferroresoance features are evaluated using phase-plan diagram.

Effect of washing water flow rate and pollution level on leakage current of a fixed washed high voltage insulator

Fixed washing system is one of the most common techniques for cleaning high voltage insulators in generation power stations. This paper presents an experimental study to investigate the effect of washing water flow rate as well as the equivalent salt deposit density (ESDD) on the leakage current passes over a high voltage insulator surface during the washing process. This investigation is carried out using a reduced experimental model that closely simulates the real washing system. Different washing water flow rates are used during the experiments and leakage currents are recorded at each case. Each washing flow rate is studied at different ESDDs that covers light to very heavy pollution levels according to the IEC 60507 standard. Also, leakage currents are recorded using a data acquisition system consists of a digital signal processing (DSP) board and a computer. Based on the obtained leakage current results, different washing methods are proposed to achieve an efficient washing system that reduces the chance of flashover occurrence.