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Insulation degradation is an irreversible phenomenon that can potentially lead to failure of power cable systems. This paper describes the results of an experimental investigation into the influence of direct current (DC) superimposed with harmonic voltages on both partial discharge (PD) activity and electrical tree (ET) phenomena within polymeric insulations. The test samples were prepared from a high voltage direct current (HVDC) cross linked polyethylene (XLPE) power cable. A double electrode arrangement was employed to produce divergent electric fields within the test samples that could possibly result in formation of electrical trees. The developed ETs were observed via an optical method and, at the same time, the emanating PD pulses were measured using conventional techniques. The results show a tenable relation between ETs, PD activities, and the level of harmonic voltages. An increase in harmonic levels has a marked effect on development of electrical trees as the firing angle increases, which also leads to higher activity of partial discharges. This study of the influencing operational parameters of HVDC converters on power cable insulation is predicted to contribute to enhancements in cable design and progressive advancement in condition monitoring and insulation diagnostic techniques that can lead to more effective asset management in HVDC systems.

A double-ended forward converter with an input inductor–capacitor filter has inherent power factor correction\ud (PFC) properties and continuous input current when operating in discontinuous-capacitor-voltage mode (DCVM). In this\ud study, the minimum separable switching configuration modelling is applied to the proposed converter operating in\ud DCVM to obtain a small-signal model of the converter. The impact of the circuit parameters on the small-signal\ud characteristic are discussed in details. The difference between the small-signal behaviour of the converter when\ud operating as a DC/DC converter and a PFC converter is investigated. The modelling methodology is intended for the\ud design of controllers in closed-loop operation. A 100 W prototype is implemented to demonstrate the feature of the\ud small-signal behaviour

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Ventilating of multi pane-glazed windows using wasted air of buildings is an effective technique to minimize heat loss through windows and save heating energy in cold regions. In low-scaled occupancy buildings with high WWR ratio, buildings supply a low flow rate of wasted air to windows ventilation systems, resulting in a declination in its thermal performance. Therefore, this study introduces methods of managing the utilisation of wasted air in windows ventilation to optimise the energy saving. Two methods have been implemented experimentally on a small-scaled room. The first method is a time-based division of air pump operation, an air pump ventilates multiple windows, one window at a time repetitively. The second method shares the available wasted air to multiple windows. The experimental results and mathematical heat transfer model have been employed to evaluate thermal performance of the system in different methods. The first method showed a best energy saving with a duty cycle of 50% for the air pump, and on/off operation every 10 s. An energy saving of 42.6% has been realized compared to the traditional double-glazed windows, and the heat transfer coefficient was declined from 3.82 to 2.8 W/m2 K. The second method showed an optimum thermal performance when the available flow rate of wasted air was shared with three double-glazed windows. An energy saving of 83.1% was achieved compared to the traditional double-glazed windows, and the heat transfer coefficient dropped from 3.82 to 2.36 W/m2 K.

this paper presents a two-stage PFC LED driver. The two outstanding features of the proposed driver are: 1 the entire system has no electrolytic capacitor, which prolongs the lifetime of the LED driver; 2 LED string current is controlled directly and PWM diming also provided. This makes the driver is virtually a current source driver. The front end stage is the conventional Boost AC/DC converter which provides a PFC (power function correction) function and operates on the Critical Conduction Mode (CRM). The cascaded DC/DC converter is a LLC resonant converter. The operations and the choice of the capacitors are studied in this paper. Experimental results are presented to verify the theoretical predictions.