Cable Modelling in PSCAD

PSCAD is one of the leading softwares in the field of EMT studies and the cable modelling sometimes becomes a nightmare for network modelling engineers. Here are some tips and tricks to make this task a simpler one.

There are three types of cable modeles in the PSCAD software namely

>> Coaxial cables (Land type installation)

>> Pipe type cables (Submarine Installations)

>> User friendly coaxial cables (simplified version of coaxial cables)

In this we will discuss the Submarine cables and the land type cable will have the similar modelling method.

1- Decide the number of conductors and insulators in the cable and select the cable model in the PSCAD.

Example:

The below data shows the cable will have two conductors and two insulator layers as provided/deducted from the data given in Figure-1.

Model the cable with two conductor and insulators like given below (C1 I1 C2 I2). As the data provided is actual thickness of the conductor/insulator layers so we selected the option (Actual thickness) as shown in Figure 2. In some case radius from the center of the cable will be given so have to choose that option instead.

The triangle formed by the trefoil cable is equilateral triangle which have equal lengths and 60 degree angle at each side. Here in this case the diameter of the cable will be the length of each side which will be equal to (50.34 mm). Now we need to find the distance between center of the cable and the center of the pipe.

We will draw a perpendicular from the cable centre (point C to center of the pipe (point O) and a perpendicular bi-sector from point O to side BC of the triangle. This bisector will divide the length into half (50.34 mm i.e radius of the cable). Now the triangle can be drawn as shown in the Figure-4.

The minimum distance between the pipe center and the cable center should be equal to this value otherwise and error will be generated by PSCAD.

After putting the length of the cable, you need to match the capacitance, RXB values and surge impedance of the cables (>40 ohms).

The capacitance of the cable is 0.260 uF/km, the voltage level is 220 kV with 60 Hz frequency its calculated value of Q is 3.14 MVAr for 0.723 km length whereas its simulated value is 3.434 MVAr.The simulated value is very much close to the calculated value as shown in the Figure 6.

Along with Q value, its calculated RXB values and surge impedance should be close enough to its simulated values (Solved constant values of PSCAD). The relative permeability of the insulators should be tweaked a bit to match the reactive power generated by the cables.