Unlike short and medium lines the line parameters of long transmission line are assumed to be distributed at each point of line uniformly. Thus modelling of a long line is somewhat difficult. But few approaches can be made based on the length and values of line parameters. For a long transmission line, it is considered that the line may be divided into various sections, and each section consists of inductance, capacitance, resistance and conductance, as shown in the RLC (resistance and inductance in series, with shunt capacitance) cascade model. Considering a bit smaller part of a long transmission line having length dx situated at a distance x from the receiving end. The series impedance of the line is represented by zdx and ydx is the shunt impedance of the line. Due to charging current and corona loss, the current is not uniform along the line. Voltage is also different in different parts of the line because of inductive reactance. Where,  z – series impedance per unit length, per phase  y – shunt admittance per unit length, per phase to neutral  formula_76  Again, as formula_77  formula_78  Now for the current through the strip, applying KCL we get,  The second term of the above equation is the product of two small quantities and therefore can be neglected. For formula_77 we have, formula_80  Taking the derivative concerning x of both sides, we get  Substitution in the above equation results  The roots of the above equation are located at formula_81. Hence the solution is of the form,  Taking derivative with respect to x we get,  Combining these two we have,  The following two quantities are defined as, formula_82 , which is called the characteristic impedance  formula_83 , which is called the propagation constant  Then the previous equations can be written in terms of the characteristic impedance and propagation constant as, Now, at formula_84 we have, formula_85 and formula_86 Therefore, by putting formula_84 at eq.() & eq.() we get,  Solving eq.() & eq.() we get the following values for formula_88 :  Also, for formula_89, we have formula_90 and formula_91. Therefore, by replacing x by l we get,  Where,  formula_92 is called incident voltage wave  formula_93 is called reflected voltage wave  We can rewrite the eq.() & eq.() as,  So, by considering the corresponding analogy for long transmission line, the obtained equations i.e. eq.() eq.() can be written into matrix form as follows:  The ABCD parameters are given by :  A = D =formula_94  B =formula_95  C =formula_96  Like the medium transmission line, the long line can also be approximated into an equivalent Π representation.