Figure 1(a) shows a buck converter, the most basic topology for converters. A buck converter always steps the voltage down. A transistor, either a bipolar junction or a power FET, is used as the switching device. A rectangular signal out of the pulse-width modulator closes and opens the switch. A comparator controls the duty cycle […]
Triac Working The triac is a three-terminal device essentially equivalent to two SCRs joined in reverse parallel (paralleled but with the polarity reversed) and with their gates connected together. The result is a bidirectional electronic switch that can be used to provide load current during both halves of the AC supply voltage. Triac connections, shown
Thyristor is a generic term for a broad range of semiconductor components used as an electronic switch. Like a mechanical switch it has only two states: on (conducting) and off (not conducting). Thyristors have no linear in-between state as transistors have. In addition to switching, they can also be used to adjust the amount of
Refrigeration| MCQ 1. A one tonne refrigerating machine means that (a) the total weight of the machine is one tonne. (b) the quantity of the refrigerant used is one tonne. (c) one tonne of water can be converted into ice. (d) one tonne of ice when melts from and at 0°C in 24 hours, the
Ammeters and voltmeters affect the operation of circuits. The degree to which the circuits are affected is called the loading effect of the instrument. For an instrument to provide an accurate indication of how a circuit operates, the loading effect should ideally be zero. In practice, it is impossible for any instrument to have zero
Removal of moisture and impurities from insulation is one of the most important manufacturing processes. Removing moisture from the oil is relatively simple, which can be done by conventional methods of filtration or heat/vacuum cycles. However, most of the moisture is in the solid insulation (it can be as high as 99%). Hence, a challenge
A partial discharge (PD) is a transient breakdown of a part of the insulation system in high voltage equipment. By this process, the entire dielectric is not breached; that is, the breakdown does not occur between two conductors. Only a small portion of the insulation suffers a miniature breakdown. Partial discharges can be thought of
Due to severe competition and restructuring taking place in the power industry, there is a need to reduce maintenance costs, operate transformers as much as possible, extend their life, and prevent unplanned outages. Hence, in the recent years the monitoring and diagnostics of transformers have attracted considerable attention of researchers and practicing engineers. The monitoring
A transformer supplying an arc furnace has to deliver unusually high currents over a wide range of voltage. Power ratings between 50 and 100 MVA are quite common now with the secondary currents of more than 50 kA. Furnace transformers have special features for handling very high currents compared to conventional transformers. Since the LV
Duties of rectifier transformers serving special industrial loads are more stringent than conventional transformers. Electrical energy in the form of direct current is required in electrolytic processes used in aluminum smelters and chemical plants (producing chlorine, soda, etc.). Various methods used for converting AC into DC in earlier days included use of motor-generator sets, rotary