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 Saravanan J

Assistant professor of EEE Department

Government College of Engineering

Tirunelveli, Tamil nadu

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Nominal 'π' method

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                       In the nominal pi model of a  medium transmission line,  the series impedance of the line is concentrated at the centre and half of each capacitance is placed at the centre of the line. The nominal Pi model of the line is shown in the diagram below. In this circuit, By Ohm’s law By KCL at node a, Voltage at the sending end By ohm’s law Sending-end current is found by applying KCL at node c or Equations can be written in matrix form as Also, Hence, the ABCD constants for nominal pi-circuit model of a medium line are Phasor diagram of nominal pi model The phasor diagram of a nominal pi-circuit is shown in the figure below. It is also drawn for a lagging power factor of the load. In the phasor diagram the quantities shown are as follows; OA = V r  – receiving end voltage. It is taken as reference phasor. OB = I r  – load current lagging V r  by an angle ∅ r . BE = I ab...
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KIRCHHOFF'S LAWS

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 Introduction:                     A German physicist Gustav Kirchhoff developed two laws enabling easy analysis of interconnection of any number of circuit elements. The first law deals with the flow of current and is popularly known as  Kirchhoff’s Current Law ( KCL) while the second one deals with the voltage drop in a closed network and is known as  Kirchhoff’s Voltage Law  (KVL). Kirchhoff’s Current Law: Statement:                     The algebraic sum of the currents meeting at a junction in an electrical circuit is zero. Σ I = 0 As per the Kirchhoff’s Current Law, i1 + i2 – i3 – i4 – i5 + i6 = 0 -----------(1)                     The direction of incoming currents to a junction is taken as positive while the outgoing currents are taken as negative. The equation (1) can also be writt...
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Critical disruptive voltage and Visual critical voltage

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  Critical disruptive voltage:                       It is the minimum phase-neutral voltage at which corona occurs. Consider two conductors of radius  r  (cm) and spaced  d  (cm) apart.  If  V  is the phase-neutral potential, then potential gradient at the conductor surface is given by: g =[V/ r log e  (d/r)] volts / cm                In order that corona is formed, the value of g must be made equal to the breakdown strength of air.  The breakdown strength of air at  76 cm  pressure and temperature of  25ºC  is  30 kV/cm  (max) or  21·2 kV/cm  (r.m.s.) and is denoted by  g o . If  V C  is the phase-neutral potential required under these conditions, then, g o  =[V c / r log e  (d/r)] volts / cm where  g o  = breakdown strength of air at 76 cm of mercury an...
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