Modelling of power cables to calculate current ratings

Introduction

Cable HV? Software can perform custom current rating calculations in accordance with IEC Standard 60287 Series for a wide range of modern extruded power cables of varying constructions can be modelled including cables for DC and AC applications, single phase or three phases, multi-core of single core cables, sheathed and armoured cables. The built-in cable editor provides considerable flexibility in specifying the parameters for the various components of which a cable may be comprised.

To model a cable and determine its current rating requires knowledge about its physical construction. This information is obtained from cable manufacturer datasheets.

This report will explain how to model several types of cables:

·??????Cable Model 1 - Single core 33 kV, XLPE insulated cable

·??????Cable Model 2 - Single core 1.5 kV DC, XLPO insulated for solar applications

·??????Cable Model 3 - Multi-core 33 kV, XLPE insulated cable

The models are validated by calculating the current ratings in various standard configurations and comparing with results in the manufacturer datasheets.

Cable Model 1: Single core 33 kV, XLPE insulated cable

The description of this cable is 19/33 kV, single-core, 95 mm2 Cu, XLPE insulated cable.

Cable manufacturer datasheet

Modelling the cable

Step 1 – Select the cable layers

On the left-hand side of the Cable Editor window select the cable layers which are present for the Cable Model. In the case of Cable Model 1 the following cable layers are present: Conductor, Conductor shield, Insulation, Insulation screen, Concentric neutral and Jacket/Serving.

Step 2 – Input the general settings

Input general settings – Phases, Cores, Voltage and Frequency – for the Cable Model.

Step 3 - Input the layer parameters

The input parameters from the datasheet are summarised in Table 1 and these values are entered into the Cable Editor by selecting the appropriate layer from the preview.

Validation of the current rating

Cable Model 1 was validated by comparing the calculated current ratings from Cable HV? Software with those for standard configurations from the manufacturer datasheet.

According to the manufacturer datasheet the installation conditions are:

·??????Ambient air temperature: 40 °C

·??????Ambient soil temperature: 25 °C

·??????Soil thermal resistivity: 1.2 K.m/W

·??????Depth of laying: 0.8 m

The Cable Model 1 current rating comparison is shown in Table 2.

As the current ratings between Cable HV? and the manufacturer datasheet are close, it can be concluded that the cable has been modelled correctly.

Cable Model 2: Single core 1.5 kV DC, XLPO insulated cable

The description of this cable is 1.5 kV DC, single-core, 400 mm2 Cu, XLPO insulated cable.

Cable layer parameters

The input parameters from the datasheet are summarised in Table 3 and these values are entered into the Cable Editor by selecting the appropriate layer from the preview.

Validation of the current rating

Cable Model 2 was validated by comparing the calculated current ratings from Cable HV? Software with those for standard configurations from the manufacturer datasheet.

The standard installation conditions are same as for Cable Model 1. The current rating comparison is shown in Table 4.

As the current ratings are close, it can be concluded that the assumption of modelling termite protection is reasonable.

Cable Model 3: Multi-core 33 kV, XLPE insulated cable

The full description of this cable is 19/33 kV, three-core, 50 mm2 Al, XLPE insulated cable. The cable datasheet document was several pages in length.

Cable layer parameters and building the model

The input parameters from the datasheet are summarised in Table 5 and these values are entered into the Cable Editor by selecting the appropriate layer from the preview.

Validation of the current rating

Cable Model 3 was validated by comparing the calculated current ratings from Cable HV? Software with those for standard configurations from the manufacturer datasheet.

The standard installation conditions are same as for Cable Model 1. The current rating comparison is shown in Table 6.

As the current ratings are close, it can be concluded that the assumption of modelling water blocking tape and outermost layer is reasonable.

Thank you for reading our article. For more information please get in touch.