Skin effect and proximity effect

When an ac current is flowing through a good quality conductor, current distribution follows a non-uniform pattern. Inner portion of the conductor has more flux linkage than outer portion. Because of this fact, we can conclude that the inductive reactance in the inner portion of the conductor more than the outer surface of the conductor. Now the effective current in the outer surface of the conductor will be more than the inner surface, thus reducing effective cross-section of the conductor. This increases the effective resistance of the conductor. This is called skin effect. Skin effect is good and blessing for ACSR conductor. In ACSR conductor, inner steel reinforced conductor does not effectively carry any current and this helps to avoid the higher resistivity of steel compared to copper. Loss of power will be more if skin effect exists. Proximity effect is the effect of non-uniform distribution of current of a conductor due to the effect of flux linkage from a neighboring conductor.

Fiber optic cable design

In a cable we can have 6, 12, 24, 48, 72 or 96 fibers. Colour identification scheme also employed now worldwide to facilitate identification of cable during installation and maintenance. Aerial and underground hoisting of cables possible. In underground cabling, two types exist. They are non-duct type and duct type. In non-duct type, burial is direct and is through high density polythene pipe. Nowadays for communication, loose tube type cables and slotted core type cables are widely used. In loose tube type cable, one or more fiber is incorporated which is then stranded helically in continuous or alternate paths. Material used for protective loose tube is thermoplastic in nature. Slotted core type cable consists of a plastic rod abstracted over a strong central fiber. Here mechanical and thermal response is very much fabulous.

Classification of battery

There are three types-primary batteries, secondary batteries and reserve batteries. Battery should have the features like long shelf life, recharging capacity, portability, compactness with less weight and economical. Primary batteries are working on the principle of conversion of the free energy change of the active materials during electrode processes into the electrical energy. Primary batteries cannot be recharged and it generates electrical energy till the active materials present in the battery. Thus in this case cell reaction is irreversible. Examples for primary battery are dry cells.  Secondary batteries are also known as rechargeable batteries or galvanic batteries. By passing an electric current through the cell in a direction opposite to that of the discharge, restoration of charge in secondary batteries can be done. Here cell reactions are reversible. Lead-acid battery, Ni-Cd battery etc. are examples. In reserve batteries, a part is detached from the rest of the battery before its activation. This helps to enhance long term storage capacity. Lithium vanadium pentoxide cells are examples.