Skin Effect The steady direct current distributes itself uniformly over the whole section of a conductor but the alternating current does not distribute uniformly rather than it tends to concentrate near the surface of a conductor. In fact in the AC system, no current flows through the core and the entire current is concentric at the surface regions. This phenomenon is called skin effect. The skin effect causes the effective resistance of the conductor to increase with the frequency of the current. The skin effect is due to eddy currents set up by the AC current. The skin effect has practical consequences in the design of radiofrequency and microwave circuits and to some extent in AC electrical power transmission and distribution systems.
The transformers which are particularly designed to provide electrical isolation between primary and secondary circuits, without a change in voltage and current level are called isolation transformers. The turns ratio of such isolation transformers is 1:1 i.e N1 and N2. Hence, isolation transformers are also called 1:1 transformers. The isolation transformer greatly reduces any voltage spikes that originate on the supply side before they are transferred to the load side. Some isolation transformers are built with a turns ratio of 1:1. A transformer of this type has the same input and output voltages and is used for the purpose of isolation only. The main function of the isolation transformer is to reduce the voltage spike before it reaches the load.
While estimating the overhead lines, the first and last pole is always earth connected and after every 3rd electrical pole, the fourth pole is earthed. Therefore, the approximate number of required ground set = 4
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