Subroutine FLT

The advantage of the FD method is that any frequency-dependent effect is easily handled as it is based on the frequency response of a transient to be solved. Thus, the frequency-dependent effect of a transmission line/cable explained in Chapter 1 is very easily included in a simulation. 

On the contrary, a sudden change in a time domain such as switching causes a difficulty because the change involves an initial condition problem that requires repeated time/frequency transforms. A nonlinear element, for example, an arrester, requires a number of the time/frequency transforms. Thus, the FD method is often used to check the accuracy of the time domain method such as the EMTP on the frequency-dependent effect. 

Ametani, A. 1987. Power System Transient Analysis. Kyoto, Japan Doshisha University. 

Ametani, A. 1990. Distributed—Parameter Circuit Theory. Tokyo, Japan Corona Pub. Co. 

Japanese Standard. 1994. High voltage testing (JEC-0102-1994). lEE Japan. 

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Complete program for computing the DLT of Equation 2.54 by the FFT method-subroutine FLT. 

The frequency responses I(s) and V(s) are sent to subroutine FLT given in Figure 2.62. Then, the FLT carries out the inverse Laplace transform and the time solutions are obtained. Figure 2.63 shows an example of a calculated result v(t) in comparison with the accurate solution. Note that the accuracy of the FLT is quite high. 

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