M. Afendi M. Piah

Hybrid regrouping PSO based wavelet neural networks for characterization of acoustic signals due to surface discharges on H.V. glass insulators

A hybrid algorithm combining Regrouping Particle Swarm Optimization (RegPSO) with wavelet radial basis function neural network referred to as (RegPSO-WRBF-NN) algorithm is presented which is used to detect, identify and characterize the acoustic signals due to surface discharge activity and hence differentiate abnormal operating conditions from the normal ones. The tests were carried out on clean and polluted high-voltage glass insulators by using surface tracking and erosion test procedure of international electro-technical commission 60,587. A laboratory experiment was conducted by preparing the prototypes of the discharges. A very important step for the WRBF network training is to decide a proper number of hidden nodes, centers, spreads and the network weights can be viewed as a system identification problem. So PSO is used to optimize the WRBF neural network parameters in this work. Therefore, the combination method based on the WRBF neural network is adapted. A regrouping technique called as a Regrouping Particle Swarm Optimization (RegPSO) is also used to help the swarm escape from the state of premature convergence, RegPSO was able to solve the stagnation problem for the surface discharge dataset tested and approximate the true global minimizer. Testing results indicate that the proposed approach can make a quick response and yield accurate solutions as soon as the inputs are given. Comparisons of learning performance are made to the existing conventional networks. This learning method has proven to be effective by applying the wavelet radial basis function based on the RegPSO neural network in the classification of surface discharge fault data set. The test results show that the proposed approach is efficient and revealed a very high classification rate.

Identification of acoustic signals of surface discharges on glass insulator under different contamination levels

Surface discharge is a common phenomenon that normally occurs on the insulator surface under wet contamination condition. The generation of small sparks from the surface discharge would develop many types of signals. In this work an acoustic method is used to detect and capture the signals of surface discharges. The tests were carried out on cleaned and polluted glass insulators by using surface tracking and erosion test procedure of IEC 587. Three conditions of contamination levels were considered, which are light, medium and heavy based on ESDD levels. A laboratory experiment was done by making the models of these discharges. The test equipment including antennas as a means of detection and digital processing techniques for signal analysis were used. Wavelet signal processing was used to recover the surface discharge acoustic signal by eliminating the noises of many natures. Experimental results shows that the actual signals of surface discharge are related to the levels of insulator contamination.

Cascaded H-bridge multilevel inverter based pulsed power supply for liquid food sterilization

This paper proposes a Cascaded H-bridge Multilevel Inverter (CHMI) based pulsed power supply for the sterilization of liquid foods using Pulsed Electric Field (PEF). The utilization of a CHMI allows the system to reach high voltage without the use of transformers while fulfilling the pulse requirements for effective liquid food sterilization. By using the CHMI topology, no extra clamping diodes or voltage balancing capacitor is needed. In this work, the proposed CHMI circuit operation is simulated using MATLAB/Simulink where unipolar and bipolar square wave pulses with pulse width range of 1 µs to 1 ms are generated. A peak output voltage of 6 kV and peak output power of 3.6 kW have been obtained with both values meeting the pulse specifications for liquid food sterilization applications.

Implementation of cascaded H-bridge multilevel inverter for liquid food sterilization using pulsed electric field

This paper presents on evaluating a performance of Cascaded H-bridge Multilevel Inverter (CHMI) pulsed power supply, which can produce high-voltage output pulses and electric field strength for effective inactivation of microbes in liquid food sterilization process. The unique feature of the CHMI allows the system to produce bipolar square wave pulses with less power consumption and high stability compared to an exponential decay pulse (EDP) and oscillatory decay pulse (ODP) in liquid food sterilization. The CHMI pulsed power supply can achieving high output voltage without using a transformer while fulfilling the requirements specification for sterilizing an identified liquid food. This in turn can reduce the power losses due to omission of winding coil as well as reduce cost. The experimental results on the 7-level CHMI indicate that, output voltage and electric field strength up of 2.0 kVp-p and 10 kV/cm respectively have been produced with both values meeting the pulse specifications for liquid food sterilization applications particularly for inactivation of Saccharomyces cerevisiae in orange juice.

Characterization of leakage current on high voltage glass insulators using wavelet transform technique

The measurement and analysis of leakage current (LC) for condition-based monitoring and as a means of predicting flashover of polluted insulators has attracted a lot of research in recent years. Leakage current plays an important role in the detection of insulators condition. This paper proposes a method for reducing the noise included in the current signal. The tests were carried out on cleaned and polluted glass insulators by using surface tracking and erosion test procedure of IEC 60587. Wavelet analysis method is used to compress the leakage current data. Experimental results shows that the actual signals of leakage current are related to the levels of insulator contamination.

Pulsed electric field by Cascaded H-bridge multilevel inverter for liquid food sterilization

This paper focuses on evaluating the effectiveness of a Cascaded H-bridge Multilevel Inverter (CHMI) based pulsed power supply for liquid food sterilization using pulsed electric field (PEF). The utilization of the CHMI allows the system to produce PEF with high stability, less heat and power consumption if compared to the conventional methods such as pulsed forming network (PFN) or transmission line techniques. The CHMI pulsed power supply can attaining high output voltage without using a transformer to meet specification necessities for sterilizing liquid food. By using the CHMI, the power loses due to omission of winding coil can be reduced. A MATLAB/Simulink software has been used to simulate the effectiveness of a 5-level CHMI circuit in order to generate PEF output pulses with pulse width 1 ms and at constant frequency of a 50 Hz. The simulation and experimental results indicate that, an output voltage up to 4.52 kV p-p and maximum output power of 348 W have been generate with the values fulfil the pulse requirements for liquid food sterilization applications. Most importantly, the CHMI has been operated with less power consumption if compared with conventional method that can prove to be beneficial in terms of lowering its cost and size particularly for industrial application to inactivate various type of microbial.