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Why Armature Winding on Stator in Synchronous Machine?

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In Synchronous Machine, the armature winding is provided on Stator and field winding on Rotor which is contrary to other Electrical Machines. In fact there are certain issues due to which we provide armature winding on Stator. The benefits of this are as follows: More Economical: It is more economical to provide Armature winding on Stator and Field winding on rotor. Let us consider a three phase Star connected 750 MVA, 21 kV Synchronous Machine. Line Current = (750x10 3 )/(1.732x21) = 20,620 A If the armature winding is placed on the Rotor, we need three slip rings each capable of handling 20,620 A. Only not this, we need to provide slip rings with an insulation of (21/1.732 = 12.12 kV). The star point for grounding is also to be taken out through the fourth slip ring. Now, suppose the power requirement for the Field is 2 MW at 500 V. Then Excitation / Field Current = 2000/0.5 = 4000A In this case only two Slip Rings each capable of handling 4000 A is re...
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Sag in Overhead Transmission Line and Its Calculation

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Sag in overhead Transmission line conductor refers to the difference in level between the point of support and the lowest point on the conductor. As shown in the figure above, a Transmission line is supported at two points A and B of two different Transmission Towers. It is assumed that points A and B are at the same level from the ground. Therefore as per our definition of Sag, difference in level of point A or B and lowest point O represents the Sag. Sag in Transmission line is very important. While erecting an overhead Transmission Line, it should be taken care that conductors are under safe tension. If the conductors are too much stretched between two points of different Towers to save conductor material, then it may happen so that the tension is conductor reaches unsafe value which will result conductor to break. Therefore, in order to have safe tension in the conductor, they are not fully stretched rather a sufficient dip or Sag is provided. The dip or Sag in Transmission line i...
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Working Principle of Transistor

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In this post I will focus on the working principle of the Bipolar Junction Transistor assuming that you are already aware of the construction details of the BJT or simply Transistors. The basic operation of the transistor will be described using the pnp transistor. The operation of the npn transistor is exactly the same if the roles played by the electron and hole are interchanged. In the figure below, the pnp transistor has been drawn without the base-to-collector bias. This situation is similar to that of the forward-biased diode. The depletion region has been reduced in width due to the applied bias, resulting in a heavy flow of majority carriers from the p- to the n-type material. As obvious from the figure above, Emitter to Base junction is forward biased, therefore majority carriers i.e. holes from the Emitter side to the Base side will start flowing and hence a current will set up from Emitter to Base. Let us now remove the Emitter to Base bias of the pnp...
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