Mohamad Kamarol

Control of ZCS-SR Inverter-Fed Voltage Multiplier-Based High-Voltage DC–DC Converter by Digitally Tuning Tank Capacitance and Slightly Varying Pulse Frequency

Conventional pulse-frequency-modulated (PFM) zero-current switching series resonant (SR) inverter-fed voltage-multiplier-based high-voltage dc power supplies have nearly zero switching loss. However, they have limitations of poor controllability at light load and large output voltage ripple at low switching frequencies. To address these problems, this letter proposes a new control scheme that is based on digitally tuning tank capacitance and slightly varying pulse frequency of SR inverter. For the realization of the proposed control approach, the tank circuit of the resonant inverter is made up of several tank capacitors that are switched into or out of the tank circuit by electromechanical switches. By digitally modulating the tank capacitance, the output voltage changes in steps. The regulation of output voltage between two adjacent steps is achieved by slightly varying the pulse frequency. The proposed control scheme has several features, namely, a wide range of output voltage controllability even at light loads, less output voltage ripple, and less current stress on the inverters power switches at light loads. Therefore, the proposed control approach alleviates most of the problems associated with conventional PFM. Experimental results obtained from a scaled-down laboratory prototype are presented to verify the effectiveness of the proposed system.

Breakdown characteristics of RBDPO and soybean oil mixture for transformer application

This paper reports the experimental result of breakdown characteristics of mixture Refined Bleached, Deodorized Palm Oil with Soybean Oil at 40°C, 50°C and 60°C. The experiment has been conducted by using BA100 Fully Automatic Portable Breakdown Voltage Test Set. The SO is mixed with the RBDPO in the range from 0 to 50%. The results obtained from the experiment are compared with the IEC standard, which is greater than 30kV. The result shows that the increments of percentage of SO to RBDPO cause gradually decrease of breakdown voltage but fulfill the IEC 156. The value for kinematic viscosity is also presented.

Determination of gas pressure in vacuum interrupter based on partial discharge

Partial discharge characteristics in air under a low vacuum region were studied to develop a diagnosis technique to determine the gas pressure in a vacuum interrupter. The pressures were set at from 1.3 Pa to 2.6 kPa in order to simulate the leakage of gas into the vacuum interrupter. The structure of the vacuum interrupter, the measurement and the circuit construction for the experimental setup were described. The measurement of partial discharge occurring inside the vacuum interrupter was performed with a current transformer, intensified charge coupled device (1CCD) camera and photomultiplier tube. The measurement of partial discharge light intensity with a photomultiplier tube was more sensitive compared with that measured with a current transformer. From this result, an attempt has been made to distinguish the pressure below and above 260 Pa on the basis of the rise time and peak intensity of discharge light pulses. A relatively longer rise time (2 mus) with a smaller magnitude (less than 0.5 mA) was attributed to a Townsend-like discharge at pressures below 260 Pa, while a sharper rise time ~(10-100 ns) with a larger magnitude (greater than 1 mA) was characterized as a streamer-like discharge above 260 Pa. In addition, the estimation of gas pressure in a vacuum interrupter was made based on phase-resolved discharge characteristics utilizing an artificial neural network.

A speed sensorless field oriented control of parallel- connected dual PMSM

This paper presents a speed sensorless field oriented control of parallel-connected dual permanent magnet synchronous motors (PMSM) fed by a single inverter. The speed of the both motors is controlled by using FOC method and averaging technique. In this project, model reference adaptive system (MRAS) method has been applied to the system in order to eliminate the use of speed sensor. The simulation work is implemented in Matlab/Simulink software in order to verify the proposed control strategy. The effectiveness of this proposed control strategy was confirmed during motor operations with balanced and unbalanced load levels at different speed range.

UHF sensor optimization used for detecting partial discharge emitted electromagnetic wave in gas insulated switchgear

Bowtie Antenna as partial discharge (PD) sensor had been modified to be an Enhanced Bowtie (EBT) which had better performance. But the development of the sensor performance should not be satisfied until here. New model should be researched continuously to achieve better performance. This paper deals with newly developed design based on the previous model, EBT. Developing new model is made by simulating wing radius and arm size. From twenty-one new simulated models, there are three new models fabricated due to initial information from simulation result which is compared with that of EBT. Simulation is performed on return-loss (dB) and effective height (mm), while experiment is conducted on return-loss, sensor gain, and charge detection sensitivity from PD in GIS 66 kV model tank. Experimental results show good agreement with simulation results. Finally, this paper proposes two of three fabricated sensors which show good performance as new optimized sensor due to better performance than EBT. One is Big Glasses model (BG) which has 42.5 mm wing radius 5.5 mm arm size, and the other is Small Glasses model (SG) which has 27.5 mm wing radius 3 mm arm size. Either BG or SG shows 40% higher detection sensitivity than EBT in PD charge. While Mid Glasses (MG) model with 40 mm wing radius 0.5 mm arm size not only fails to fulfill effective height requirements but also shows just similar result as EBT.

Organo-montmorillonite as an electrical treeing retardant for polymeric insulating materials

This paper presents investigation on the propagation of electrical treeing in silicone rubber samples filled with Montmorillonite (MMT) and Organo-montmorillonite (OMMT) nanoclays as fillers for electrical tree inihibition. Treeing experiments were conducted by applying ac voltage with increasing rate of 0.5 kV per second at power frequency on pure silicone rubber, silicone rubber filled with 1% MMT and silicone rubber filled with 1% OMMT samples respectively and treeing propagation length and inception voltage within 30 minutes aging period were observed. Result from this study showed that the silicone rubber/OMMT sample exhibited the shortest tree length as well as highest tree inception voltage followed by the silicone/MMT sample with the pure silicone rubber having the least electrical performance. This finding suggests the OMMT can be used a filler in polymeric insulating materials for electrical tree inhibition.

Breakdown voltage characteristic of MO and RBDPO mixture for power transformer insulation

This paper presents the breakdown voltage characteristics of Refined, Bleached, and Deodorized Palm Oil (RBDPO) and mineral oil (MO) mixture. The ratio of 10% to 100% of RBDPO was mixed with MO at 40°C, 50°C and 60°C. The experiment was conducted according to IEC 156 standard by using BA100, Fully Automatic Portable Breakdown Voltage Test Set. The results from the experiment show the breakdown voltage for all mixtures and temperatures were fulfilled the IEC standard, which is greater than 30kV. The result shows that the descending percentage of MO to RBDPO cause gradually increases of breakdown voltage and fulfill the IEC 156 standard. The breakdown voltage for all temperatures was abruptly decreased at 30%RBDPO/70%MO mixture. The optimum breakdown voltage of the oil mixture was obtained at 80% RBDPO/20%MO.

Diagnosis of Vacuum Degree in Vacuum Interrupter Based on Partial Discharge

Partial discharge characteristics in air under low vacuum region were studied to develop vacuum leakage detector system. The pressures were set at 1.3 Pa to 2.6 kPa in order to simulate the leakage of vacuum interrupter. The measurement of discharge occurring inside the vacuum interrupter was performed with current transformer, ICCD camera and photomultiplier tube. The detection of discharge light intensity with a photomultiplier tube was more sensitive compared with a current transformer. From this result, an attempt has been made to distinguish the pressure below and above 260 Pa on the basis of the rise time and peak intensity of discharge light pulses. Discharge pulse with longer rise time with larger pulse width were attributed to Townsend-like discharge at pressures below 260 Pa while that with the sharper rise time with smaller pulse width were characterized as streamer-like discharge above 260 Pa. In addition, the estimation of vacuum degree in vacuum interrupter was done based on phase-resolved discharge characteristics by utilizing artificial neural network

Study of Dielectric Properties of a Potential RBD Palm Oil and RBD Soybean Oil Mixture as Insulating Liquid in Transformer

This paper reported the experimental result of dielectric properties of Refined, Bleached and Deodorized Palm Oil (RBDPO) combined with 0-50% of Refined, Bleached and Deodorized Soybean Oil (RBDSO). The dielectric strength and relative permittivity of RBDPO/RBDSO was higher compared to mineral oil at all ranges of ratios and temperatures which indicated a positive sign for its possible use as insulating liquid in a transformer. All ratios of the RBDPO/RBDSO mixture also demonstrated lower dissipation factor compared to mineral oil at 40˚C, 70˚C and 90˚C. Apart from that, the kinematic viscosity for the oil mixtures shown exceeded the IEC 60296 as well as the mineral oil results. 70%RBDPO/30%RBDSO mixture ratio was chosen as the best mixing percentage after comparison was made with the mineral oil and IEC 60296 standard where the mixture accumulated the most satisfactory of dielectric properties hence making it as the potential candidate for palm and soybean-based transformer oil.

Development of partial discharge detection and diagnostic methods of vacuum circuit breaker

There is a possibility of partial discharge (PD) occurrence due to an abnormality of the insulation and the aging of the vacuum circuit breaker (VCB) in cubicle-type gas insulated switchgear (C-GIS). PD may contribute to a risk that leads to breakdown in the worst case, and cause failure of the equipment. Thus, knowing the characteristics of the PD internal VCB is required. In this work, a development of PD detection and diagnostic method of VCB is introducedA model VCB consisting of a vacuum interrupter (VI) was connected in series with a transformer. The internal pressure of VI was set by a turbo molecular pump via flexible hose, insulating tube and leak valves. The internal pressure of VI was verified up to 10-2 Pa by a digital metal ionization gauge. The diagnostic method was studied using a number of sensors with different specification. We have used detection resistance, horn antenna, transient earth voltage (TEV) sensor and three different frequency bands to detect PD signals.