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The effect of sintering temperature on the microstructure, density and nonlinear electrical properties of 0.1 mol% Nb 2 O 5 added ZnO-V 2 O 5 varistor ceramics had been investigated. Density measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD) pattern analysis characterized the sintered samples. The electric current and capacitance measurements of the varistor samples were done in varying voltage over a wide range. Image analysis by SEM shows an increase in the average grain size from 2.8 to 7.2 µm when the sintering temperature increases from 850 to 975 °C. The varistor sample, sintered at 850 °C, exhibits breakdown field of 4258 V/cm with nonlinear exponent value of 24. Degradation in breakdown field (1440 V/cm) and nonlinear exponent (9) have been observed with an increase in sintering temperature up to 975 °C. Barrier height estimated from the electric field-current density (E-J) and the capacitance-voltage (C-V) measurements follow an inverse relationship with sintering temperature.

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This paper discusses the design and implementation of single phase PWM inverter using 8051 microcontrol-ler. The main features of 8051 based PWM inverter are simpler design, low cost, maximum range of voltage control and compact in size. The designed PWM inverter is tested on various AC loads like AC motor and intensity control of incandescent lamp in a closed loop environment

The superconducting cyclotron at VECC consists of three rf cavities separated at 120 • and each cavity is fed power from an individual rf amplifier, based on a tetrode tube, in the frequency range of 9-27 MHz. All the three tetrode tubes are powered by individual power supplies for their biasing which are fabricated and commissioned with the rf system of the cyclotron. The dc power to the anodes of all three tubes is fed from a high voltage power supply rated at 20 kV dc, 22 A along with suitable interlocks and crowbar protection. The tubes are protected by a single ignitron based crowbar system against an internal arc fault by diverting the stored energy very fast, minimizing the deposited amount of energy at load and allowing the fault to clear. The performance and protective capability of the crowbar system is demonstrated by using wire survivability test. The design criteria of anode power supply along with the crowbar protection system, in-house development, testing and performance is presented in this paper.