Miniature/Low Oil Circuit Breaker

In the bulk oil circuit breaker, the oil has to perform two functions, first of all it act as an arc quenching medium and secondly it insulate the live part from earth. It has been found that only small percentage of oil is actually used for arc extinction while the major part is utilized for insulation purposes. For this reason the quantity of oil in bulk oil circuit breaker reaches a very high as the system voltage increases. This not only increases. This not only increases the expenses, tank size and weight of the breaker but it also increases the fire risk and maintenance problems.
A low oil circuit breaker employs solid materials for insulation purposes and uses a small quantity of oil which just sufficient for arc extinction. Regarding quenching the arc, the oil behaves identically in bulk as well as low oil circuit breaker. By using suitable arc control devices the arc extinction can be further facilitated in an low oil circuit breaker.
Construction Above figure shows the cros…

Vacuum Circuit Breaker

In Vacuum circuit breakers, vacuum (degree of vacuum being in the range 10-7 to 10-5 torr) is used as the arc quenching medium. Since vacuum offers the highest insulating strength it has far superior arc quenching properties than any other medium. For example, when contacts of a breaker are opened in vacuum, the interruption occurs at first current zero with dielectric strength between the contacts building up at a rate thousands of times higher than obtained with other circuit breaker.
Principle:- The production of a arc in vacuum circuit breaker and its extinction can be explained as follows;- When the contacts of the breaker are opened in vacuum (10-7 to 10-5 torr), an arc is quickly extinguished because the metallic vapor, electrons and ions produced during arc rapidly condense on the surface of the circuit breaker contacts resulting in quick recovery of dielectric strength. As soon as the arc is produced in vacuum, it is quickly extinguished due to the fast rate of recovery of d…

SF6 Circuit Breaker

In such circuit breaker SF6 gas is used as the arc quenching medium. SF6 is an electro-negative gas and has strong tendency to absorb free electrons.The contacts of the breaker are open in the high pressure. Flow of SF6 gas and arc is struck between them. The conducting free electrons in the arc are rapidly captured by the gap to form relatively immobile ions.The loss of conducting electron in the arc quickly builds up enough insulating strength to extinguish the arc. SF6 circuit breaker has been found to be very effective for high power and high voltage service.
Construction:- Above figure shows the parts of typical SF6 circuit breaker. It consists of fixed and moving contacts enclosed in a chamber(called arc interruption chamber) containing SF6 gas. This chamber is connected to SF6 gas reservoir. When the contact of breaker are opened, the valve mechanism permits a high pressure SF6 gas from the reservoir to flow towards the arc interruption chamber. The moving contact is a hollow …

Classification of Electric Drives

Group DrivesIt consists of single machine which actuates several machines or mechanism by means of one or more line shaft. Hence this is also called "line shaft drive". This line shafts are connected to multi stepped pulleys and belts that connect this pulley and shaft of the driven machine, serves to vary their speed.

Group drive is economical in consideration for the cost of motor and control gear. A single motor of large capacity costs less than that of the total cost of number of small motors for same total capacity namely, a single motor of 100KW costs less than that of ten motors of 10KW each. Since all the motors may not operate on full load at the same time, the KW rating of motor of group drive is often less than the aggregate KW output rating of the individual motor and further cause reduction in cost.
Individual DriveIn individual drive an electric motor used for transmitting motion to various parts or mechanism belonging to single equipment. For example, such drive…

Passive Method of Space Heating

A schematic diagram of passive space heating designed by Professor Trombe is shown in figure. The south face of the house to be heated is provided with single or double glazing. Behind it is a thick black concrete wall which absorbs Sun radiation and serve as thermal storage. Vent A and B which can be opened and closed are provided near the top and bottom of the storage wall. The whole unit consisting of storage wall with vents and glazing is referred as Trombe Wall.

During day time both vents A and B are kept open. The air between inner glazing and wall is heated and flows into living space from top vent. Simultaneously the cool air in the room is pulled out from the living space through bottom vent. Thus a natural circulation path is set up. Some energy transfer in the living space also takes place by convection and radiation from the inner surface of the storage wall. During night energy transfer take place by convection and radiation from the inner surface.

The Trombe Wall can also …

Solar Water Heater Working (Thermosymphonic Mode)

A Solar Water Heater(SWH) is a device which provides hot water for bathing, washing, cleaning etc. using solar energy. It is generally installed at terrace or where sunlight is available and heats water during day time which is stored in an insulated storage tank for use when required including morning. It basically heats the water using heat energy of the Sun rays. Today we are going to discuss the working of solar water heater in thermosymphonic mode.

A solar water heater is shown in above figure. It consists of a tilted liquid flat plate collector(LFPC) facing south with transparent glass covers, a separate highly insulated water storage tank and well insulated pipes connecting the two. The bottom of the tank is at least 1-2 feet the top of the collector and no auxiliary energy is required to circulate water through it. Circulation occurs through thermosymphonic mode or natural convection. As the water us heated in its passage through the collector its density decreases and hence it…

Wireless Power Transfer

First demonstrated by Nicholas Tesla in the 1890s, wireless power transfer is an innovative technology that has permeated major areas in the consumer and industrial electronic market.
The various forms of WPT include solar energy, microwaves, and magnetic energy. In this article, we will focus on wireless power transfer using magnetism and induction coils. The following offers an insight into the working principle, features, and applications.
Working principle  Wireless power transfer works on the inductive power transfer principle, as found in the conventional transformers. The only difference is that while in the transformer the two coils are in very close proximity and contain a ferrite material to increase the coupling, inductive chargers have an air gap between the two coils. The process follows the following procedure:
The mains voltage is converted into alternating current, preferably, high-frequency AC
This current (the high-frequency AC) is transferred to the coil  via transmit…