Digsilent-Cable-Tutorial.pdf

DIgSILENT PowerFactory Application Guide

Cable Modelling Tutorial DIgSILENT Technical DIgSILENT Technical Documentation

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Copyright ©2013, DIgSILENT GmbH. Copyright of this document belongs to DIgSILENT GmbH. No part of this document may be reproduced, reproduced, copied, or transmitte transmitted d in any form, by any means electronic or mechanical, without the prior written permission of DIgSILENT GmbH. Cable Modelling Tutorial (DIgSILENT (DIgSILENT T Technical Documentation)

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Contents

Contents 1 Introd Introduct uction ion

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2 Cable Cable Compon Component ents s

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2.1 Single Single Core Core Cab Cable le . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2.2 Comparison Comparison betw between een vendor vendor and and PowerFactory PowerFactory data data . . . . . . . . . . . . . . . .

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2.3 Laying Laying methods methods in three three phase phase systems systems . . . . . . . . . . . . . . . . . . . . . . .

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2.4 Pipe Pipe type type cables cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2.5 Rat Rating ing and Bondin Bonding g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3 Input Input of Cabl Cable e Para Paramet meters ers in PowerFactory

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3.1 Cable Cable Type Definition Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.2 Output Output Mat Matrix rix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.3 Pipe Type Cab Cable le . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4 Bondin Bonding g of cables cables in PowerFactory

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4.1 Cable Cable System System definition definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4.2 4.2 Bond Bondin ing g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Cable Modelling Tutorial (DIgSILENT (DIgSILENT T Technical Documentation)

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Cable Cab le Com Compon ponent ents s

Intr Introd oduc ucti tion on

This tutorial has been prepared with the objective to give an understanding to the PowerFactory user about the cable modelling. modelling. First we start giving a description of the general aspects aspects for the different types of cables, then some examples are used in order to show the capabilities of PowerFactory for PowerFactory for cable modelling.

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Cabl Ca ble e Comp Compon onen ents ts

In this chapter, chapter, a brief description description of the components components found found in a cable will be pointed pointed out. Additional tionally ly,, a compari comparison son bet betwee ween n the main main parts consti constitut tuting ing the cable cable geo geomet metry ry and the mod modell elling ing capabilities of PowerFactory of PowerFactory will will be defined. defined.

2.1 Single Single Core Core Cable Cable Every electric power cable is composed of at least two components: an electrical conductor and the conductor insulation which prevents direct contact or unsafe proximity between conductor and other objects [1]. Regarding modelling purposes in PowerFactory in PowerFactory ,, a cable is divided mainly in two categorie categories: s: single single core cables cables and three three core core cables cables.. For For simpli simplicit city y reason reasons, s, we will start describing the components of a single core cable type and then expand its definition for the applica applicatio tion n of three phase phase cable cable systems systems.. The geometry geometry of a single single core cable cable type type in PowerFactory is PowerFactory is as depicted in figure 2.1. figure 2.1.

Figure 2.1: Layers of a single core cable cable in in PowerFactory PowerFactory

• Conductor: Conductor: the hollow hollow red portion portion of the cable cable consists consists in a sectio section n with with a conduc conductin ting g element, usually copper or aluminum, which is defined by means of the resistivity material and the section section thicknes thickness. s. If the core core we were re to be solid, solid, withou withoutt hollow hollownes ness, s, the core diameter shall be defined simply by only the overall section of the core. • Conductor Screen: Screen: A semi-conducting semi-conducting tape to maintain maintain a uniform uniform electric field and minimize electrostatic stresses. It has a very thin section and is located between the conductor and the insulation.


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• Insulation: Insulation: this section section is intended intended to prevent the flow of electricity electricity from the energized energized conductors to the ground or to an adjacent conductor. Typically, the material of this section is of the thermoplastic (PVC) or thermosetting (EPR, XLPE) type. • Insulatio Insulation n Screen Screen: A semi-conducting material having a similar function as the conductor screen. screen. It is located located between the insulation insulation and the sheath. • Sheath: Sheath: This layer has two main objectives: 1. To carry the neutral neutral and/or fault current current to earth in the event of an earth fault fault in the system. 2. To be used as a shield to keep electromagnetic radiation in and, in the case of paperinsulated cables, to exclude water from the insulation. Usually, when a solid sheath is used in the cable construction, it is made of lead or aluminum. minum. In some special cases, copper may be used. Because Because of safety safety consideratio considerations, ns, metallic sheaths are always grounded in at least one place. • Oversheath: Oversheath: This layer covers the metallic sheath and acts as a filler between the metallic sheath sheath and the armor. Most commonly commonly used materials materials are PVC and PE. • Armour: Armour: This layer is intended to provide mechanical protection of the conductor bundle. Usually, it is used for submarine and special purpose cables. • Serving: Serving: This is usually a plastic cover and provides mechanical, thermal, chemical and electrical protection to the cable.

2.2 Compariso Comparison n between between vendor vendor and PowerFactory data The first task an engineer must confront with, in order to model a cable and for being the most representative as well of the real condition, is to identify the constitutive parts of it and bring them to a simulation software. PowerFactory defines PowerFactory defines each part of the cable modelling tool with universally accepted names, however this process of identification still can be a difficult task as it may lead to errors of interpretation. In order to help with this identification process, a comparison between the PowerFactory and PowerFactory and the most common used names in cable datasheets is shown in Table 2.1 Table 2.1 Name in PowerFactory Sheath Oversheath Serving

Name in Datasheets Screen Armor bedding Armor serving - Jacket

Table 2.1: Comparison of cable component names for a single a single core cable type type

2.3 Laying Laying methods methods in three three phase phase systems systems Laying methods for three phase systems with single core cables are usually found in two categories: egories: trefoil trefoil and flat. Trefoil refoil is used to minimize the sheath circulating circulating currents currents due to the magnetic flux linking the cable conductors and metallic sheath. Flat formation is appropriate for heat dissipation and consequently to increase cable rating.


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(a) Trefoil

(b) Flat

Figure 2.2: Laying arrangements in three phase systems with single core cables

PowerFactory is PowerFactory is able to define a widespread of laying arrangements for single core cables, using a coordinate coordinate system. For cables cables installed installed in pipes, pipes, such as submarine submarine cables, cables, a slightly different configuration must be defined, in order to cope with all the internal arrangement for these types of cables. cables. Nonet Nonetheless heless,, both arrangements arrangements are to be defined in a cable cable system element. element. The definition definition of the common geometry and the difference differences s with the single core cable type are described in the next section.

2.4 Pipe Pipe type type cables cables As mentioned in the last section, some cable installations, for example, submarine cables, are constructed in a pipe type arrangement. The distribution of the internal components is slightly different in comparison with the single core cable type. The pipe type cables are related to three phase cables, where each one of the phases is included inside the pipe. In PowerFactory , PowerFactory , the definition of a pipe type cable is done by means of using a single core cable type, and then using these characteristics on a pipe arrangement in a cable a cable system . What the user must be aware of, is that normally each of the single core cables inside a pipe have layers ending at the oversheath the oversheath . No armor is included individually for each phase, but an overall armor surrounding the pipe is used. Then, a filler is used to define the bundle geometry, usually usually of a soft polymer polymer material. The arrangement arrangement (similar as the trefoil trefoil described described in 2.2a) 2.2a) is surrounded surrounded by the armour and serving (jacket), (jacket), the latter being as the outmost outmost layer of the pipe cable. cable. This implies implies that the modelling modelling of a pipe type cable will need the definition definition of a single core cable without armour and serving, and the definition of these components have to be made inside the cable system. Below is a representation in PowerFactory of PowerFactory of the single core cable type without armor and serving layers and the cable system used for a pipe type cable with serving and armour layers.


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(a) Single core cable

(b) Pipe cable

Figure 2.3: Cable system representation for a pipe laying arrangement

In figure 2.3a figure 2.3a,, the layers from the center to the outermost layer are in the following order: Conductor, Conductor screen, Insulation, Insulation screen, Sheath and Oversheath. In figure 2.3b figure 2.3b,, the white area between the single core cable trefoil arrangement and the armor is the filler, whereas the black area represents the armor. No graphical representation is available for the serving in pipe type cables.

2.5 Rating Rating and Bondi Bonding ng For three phase systems composed of single core cables with metallic sheaths, the bonding arrangement and the thermal resistivity of the trench fill are the most important factors influencing cable rating. The bonding of the cable to earth is the process where the metallic shield (sheath and/or armor) is grounded grounded at one or bot both h end ends. s. Diffe Differen rentt variat variation ions s exist exist,, whe where re the double bonded and cross bonded bonded bonding bonding types can be found found.. Since Since the electri electric c pow power er losses losses in a cable cable are dependent, dependent, amongst other factors, factors, on the currents flowing in the metallic sheaths, sheaths, by reducing the current flows in these layers, layers, the ampacity of the cable cable can be increased. increased. A double bonded configuration will reduce induced voltages, but will provide a path for the circulating current throug through h the sheaths, sheaths, thu thus s reduci reducing ng the current-c current-carryi arrying ng capaci capacity ty of the cable. cable. In the the cross bonded configuration, bonded configuration, the sum of the induced voltages in the shielding of the phases will be zero and thus the current flowing through the shielding will be minimized, improving the available cable rating. The use of armor wires on cables with lead sheaths, installed in three phase systems with close spacing, causes additional sheath losses because the presence of armor wires reduces sheath resistance, since both armor and sheath are connected in parallel, and the losses are largest when the sheath circuit resistance is equal to its reactance. Without armor wires, the reactance of the sheath is always always very much smaller than the resistance. resistance. To minimize minimize this increase in losses, losses, armor wires made of high resistance resistance material material such as copper-sili copper-silicon-ma con-mangane nganese se alloy alloy are sometimes sometimes used. Please Please note that the losses losses in the sheath and armor combination combination could be several times the conductor losses, depending on the bonding arrangements of the sheaths and armor [1]. PowerFactory is PowerFactory is capable of modelling a simple, double or cross bonded configuration, for cable systems systems using single core cables. cables. For a pipe cable, and for the single core cable systems, systems, a bond between between the sheath sheath and the armour is also availab available. le. A schematic example example of a crosscrossbond bonded ed confi configu gura rati tion on is show shown n in the the figur figure e belo below w. The The dash dashed ed line lines s repr repres esen entt the the shea sheath th and/ and/or or armor.


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Input Inp ut of Cab Cable le Para Paramet meters ers in in PowerFactory

Figure 2.4: Cross bonding connection scheme

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Input Input of Cable Cable Paramet arameter ers s in PowerFactory

For the modelling of a cable, we will describe the steps needed to achieve a proper representation in in PowerFactory . PowerFactory . For For this, a model examp example le has been prepar prepared ed for use. use. The system system consists in two independent cables of 1 km length each, connected between two 66 kV busbars to feed a 40 MW load. The external external grid is connected connected at the Busbar Busbar A, providing the electric electric power to the system. Note: Please import the project file ”Cable Tutorial 0.pfd” to PowerFactory and PowerFactory and activate it.

3.1 Cable Cable Type Definition Definition The first step is to define the cable type. We will model the cable as to be representing a 3-phase single single core cable, cable, disposed in a flat arrangement. arrangement. The representativ representative e values to be entered in PowerFactory are PowerFactory are extracted from a vendor catalog [2]. All the data related to the cable as seen in the catalog is summarized in the table below. Description Cable Type Nominal Voltage Cros Cross s Sect Sectio ion n of Co Cond nduc ucto torr Diameter of Conductor Insulation Thickness Diam Diamet eter er Over Over Insu Insullatio ation n Cross Section of Screen Outer Diameter of Cable

Value XLPE Single Core 66 kV 150 150 mm mm2 2 14.2 mm 9.0 mm 34.6 34.6 mm 35 mm2 46.0 mm

Table 3.1: Datasheet values for a XLPE 66 kV 150 mm2 cable

Please Please note that the cable cable has no armour nor shield shield in its structure structure.. It can be seen from the information presented in the table above that first of all we need to identify the values which PowerFactory need PowerFactory need in order to make a proper modelling, modelling, and then insert them on our model. model. To create a new cable type, please follow these steps: • Doub Double le click click on the Single the Single Core Cable A line A line element. Cable Modelling Tutorial (DIgSILENT (DIgSILENT T Technical Documentation)

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• Click Click on the down arrow arrow in the the Type Type field and choose New New Project Project Type Type . . . Definition (TypCabys) (TypCabys).. A new dialog appears. appears.

→ Cable

• Inside Inside the the Cable Definition dialog, Definition dialog, we can define all the relevant parameters of the cable geometry, number of circuits, disposition (Buried (Buried in Ground, in Pipe ), ), type of cable per circuit, circuit, etc. Right click click on the cell corresponding corresponding to the TypCab the TypCab of of the Circuit 1 row 1 row and click Select click Select Element/T Element/Type ype . . . , as shown in figure.

Figure 3.1: Cable Definition dialog • Since Since there isn´t isn´t any Single any Single Core Cable crea Cable created ted yet, yet, we have have to create create one first. first. This This can be done directly directly from the actual dialog, clicking clicking on the New the New Object icon Object icon shown in the figure below. A new dialog appears again.

Figure 3.2: New Object button button • The new dialog of the Basic Data tab Data tab page, contains all the geometrical data for the Single Core Cable at at the Conducting, Conducting, Semiconduc Semiconducting ting and Insulation Insulation layers. layers. We have to determine which parameters must be entered to properly define the Single Core Cable .


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Figure 3.3: Singe Core Cable dialog • Define the rated rated voltage voltage with a value value of 66 kV. kV. • For the conductor, conductor, from the vendor information information the diameter of the conductor is 14.2 mm. This will give a Thickness of of the Conducting the Conducting Layer section Layer section in in PowerFactory of PowerFactory of “7.1” mm. Insert this value in the cell of the Thickness the Thickness of of the Conductor the Conductor row. row. Also, define the material of the conductor with “Copper”. • The next next layer layer is the Insulation the Insulation . As you can see from the vendor vendor data, the value is 9.0 mm and can be directly inserted in PowerFactory in PowerFactory .. However, if you compare this thickness with the thickness resulting from the Diameter the Diameter Over Insulation minus minus the Diameter the Diameter of Conduc- tor , you will notice a slight difference of about 1.2 mm. Thus, we should insert “10.2” mm as Insulation as Insulation thickness. thickness. This thickness is decisive in the equivalent capacity of the cable. Define the Material the Material as as to be of “XLPE ( >18/30(36)kV cab.(fil.))” type. • The Sheath is Sheath is made of copper, but since there is no copper category inside the material element, we have to manually define the Resistivity Resistivity of the Sheath the Sheath . Inp Input ut the valu value e of “1.7241” uOhm*cm uOhm*cm in the corresponding corresponding cell. For the thickness, thickness, note that the vendor data is in terms of a cross section. section. By means of a geometric calculati calculation, on, we can determine the thickness thickness of this layer, layer, being “0.32” mm approximat approximately ely.. Input this value in the corresponding cell. • The final final layer layer is the Oversheath . Define Define the material material as to be of the same type of the Insulation layer, layer, and input “5.38” mm as the thickness value. • Finally Finally,, change the name of the Single the Single Core Cable to Cable to “Cable XLPE 66 kV”. • Note that the the Outer Outer Diameter field Diameter field of the Core is the double of the Conductor thickness, as should should be. Also, Also, note the the Overall Overall Cable Diameter value Diameter value at the lowest part of the dialog. If the values were entered correctly, the cable should show an overall diameter of 46.0 mm, coincident with the vendor catalog data.


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Figure 3.4: Singe Core Cable XLPE 66 kV data • Press Press OK OK.. Now the Cable the Cable System dialog System dialog is automatically updated with the new geometrical information. Since all the coordinates are set to zero, the phases show as they are at one point only.

Figure 3.5: Cable System dialog

Input the following coordinates for the line circuits: Cable Modelling Tutorial (DIgSILENT (DIgSILENT T Technical Documentation)

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Coordinate Value

X1 -0.116

X2 0

X3 0.116

Y1 1

Y2 Y2 1

Y3 Y3 1

Table 3.2: Coordinates for the Single Core Three Phase System

The final arrangement should see as in the figure below.

Figure 3.6: Cable System with Coordinates

Assign the same cable system for the Single Core Cable B element B element and perform a load flow. The system should show the following results.


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Figure Figure 3.7: Load flow results

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Outp Output ut Ma Matri trix x

In order to check if the parameters entered entered will be representin representing g the cable electrical parameters parameters in reality, we can compare the capacitance and inductance values given from the vendor catalog and the values determined in PowerFactory in PowerFactory .. Please follow the following steps: • Edit any of the lines by double clicking clicking on them, then click on the left arrow of the Type field of the dialog. • From From the Cable System element, element, press the button Calculate button Calculate.. • PowerFactory will PowerFactory will automatically reproduce the matrixes defining the cable system and showing all the data in the output window. • Press Press OK OK and and OK OK.. For the output information, two sections can be identified: a phase and a sequence parameters matrix. The following figures indicate in detail the internal sections of the matrixes, and how the parameters should be identified.


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Figure Figure 3.8: Matrix of impedance parameters parameters per phase

Figure 3.8 Figure 3.8 refers refers to the impedance parameters parameters per phase. phase. For each row, the real (resistance) (resistance) and imaginary imaginary (reactance) (reactance) part is given given in Ohm/km. Ohm/km. The index indicated indicated in parenthesis parenthesis has a correspondence with the legend at the top, e.g. (1) is equivalent to the Phase 1, as defined in the Cable the Cable System .

Figure Figure 3.9: Matrix of admittance parameters parameters per phase

Similar description applies for phase admittance matrix shown in Figure 3.9. For each row, the real (conductance) and imaginary (capacitance) part is given in uS/km.


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Figure 3.10: Matrix of impedance parameters per sequence

Figure 3.10 Figure 3.10 refer refers s to the impedance impedance parameters per sequence. sequence. For each row, row, the real (resistance) and imaginary (reactance) part is given in Ohm/km. The index indicated in parenthesis has a correspondence with the legend at the top, e.g. (1) is equivalent to the positive sequence.

Figure Figure 3.11: Matrix of admittance admittance parameters parameters per phase

Similar description applies for sequence admittance matrix shown in Figure 3.11. For each row, row, the real (conducta (conductance nce)) and imaginary imaginary (capacit (capacitanc ance) e) part is given given in uS/km. uS/km. Not Note e tha thatt the conductance values are zero, since there is no dielectric losses defined for the insulation material material in the the Single Single Core Cable type. Cable type. The comparison comparison must be performed with the sequence parameters. parameters. For the resistance, resistance, reactance and susceptance values, we extract the following information from the figures presented above:


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Resist Resi stan ance ce Reac Re acta tanc nce e Susc Suscep epta tanc nce e

Pos.seq. 0.10 0.1096 96 Ohm/ Ohm/km km 0.20 0.2057 57 Ohm/ Ohm/km km 58.8 58.872 723 3 uS/k uS/km m

Neg.seq. 0.10 0.1096 96 Ohm/ Ohm/km km 0.20 0.2057 57 Ohm/ Ohm/km km 58.8 58.872 723 3 uS/k uS/km m

Zero seq. 0.25 0.2573 73 Ohm/ Ohm/km km 1.85 1.8573 73 Ohm/ Ohm/km km 58.8 58.872 723 3 uS/k uS/km m

Table 3.3: Cable sequence parameters

Now, from the vendor catalog data, it can be seen that the capacitance and inductance values are 0.21 uF/km and 0.65 mH/km correspondingly, which is equivalent to a 65.97 uS/km susceptance ceptance and 0.20 Ohm/km reactance. reactance. Comparing Comparing these values, we see that the reactances reactances have very close values, however the susceptance has a difference of about 11% with respect to the vendor data. We can adjust the value by changing the Relative the Relative Permitivitty of Permitivitty of the insulation layers, layers, without without affecting affecting the geometry geometry of the cable. This adjustment adjustment is a valid approach since we don´t have the specific data of the insulation layers, as mentioned in section 3.1. • Edit the cable cable element by clicking clicking on the Object the Object Filter button. Filter button. • An icon list is displa displayed. yed. Search for for the Single the Single Core Cable Type Cable Type and click on the icon. • From From the new dialog, dialog, right click click on the Single the Single Core Cable element Cable element and select Edit select Edit . • Change Change th the e Material of of the insulation layer to Unknown to Unknown and and input the value of 3.35 for the Relative Permitivitty . • Click Click OK OK and and close the Object the Object Filter window. Filter window. • Perform erform a calculation calculation of the electrical electrical parameters of the cable cable system, in order to display the new susceptance values. • Check Check that the positive positive susceptance susceptance has now changed changed to 65.74 uS/km. uS/km.

3.3 Pipe Pipe Type Cable Cable Pipe type cables are used normally as submarine cables. They are constructed in such manner that the three phases are inside a pipe, usually made of steel. The modelling for these type of cables in PowerFactory in PowerFactory is is similar to the single core cables. Note: Please import the project file ”Cable Tutorial 1.pfd” to PowerFactory and PowerFactory and activate it.

The system is now in 132 kV, feeding a load of 40 MW through a line element of 50 km. Now, we have to define the cable type and cable system for a pipe type cable. The relevant data for the selected cable is summarized below.


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Description Conductor Cond Co nduc ucto torr Scre Screen en Insulation Insu Insula lati tion on Scre Screen en Metallic Sheath Inner Jacket Bedding Armour Servi rving Outer Diameter

Thickness 15.2 mm 1 mm 17.0 mm 1.0 1.0 mm 2.9 mm 2.9 mm 2.0 mm 7.0 mm 4.0 mm 207 mm

Material Copper Extr Extrud uded ed semi semi-c -con ondu duct ctin ing g comp compou ound nd XLPE compound Extru Extrude ded d semi semi-c -con ondu duct ctin ing g comp compou ound nd Lead Semi-co -conduction polyethylene Polypropylene strings Galvanised steel wires Single layer of polypropylene strin rings -

Table 3.4: Datasheet values for a three-core XLPE 132 kV 630 mm2 cable

First, we begin defining the single core cable, which will represent each one of the phases inside the pipe arrangement. • Edit the line line and assign assign a new Cable new Cable Definition . Name it to “Pipe system”. • Select Select from the drop-down drop-down menu in the Buried the Buried field, field, the option “in Pipe”. • Note that a new field has appeared, appeared, which contains contains all the geometrical geometrical data for the pipe. Also, the coordinates system has changed to polar values. • Create Create and assign assign a new Single new Single Core Cable Type to to the pipe system. • In the Single the Single Core Cable Type dialog, dialog, change the Name the Name to to “Three core XLPE 132 kV” and the Rated the Rated Voltage to to 132 kV. • Input the parameters parameters in the dialog, dialog, as in Table Table 3.4 3.4.. • Note that you can select the type of material material by double-clicki double-clicking ng on the corresponding corresponding cell of the Material the Material column. column. • Leave Leave the Serving the Serving and and Armour Armour layers layers unchecked, since we are going to define them in the Cable System. • The dialog dialog should see as shown shown in Figure 3.12. Figure 3.12.


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Figure 3.12: Parameters for Pipe Single Core Cable Type • Once all the values have have been entered on the dialog, dialog, press OK press OK.. This will send you back to the Cable the Cable System dialog. dialog. • First input input the polar coordinates coordinates (Magnitude (Magnitude / Angle) for each phase. In order to calculate calculate this value, we must first know the overall cable diameter per phase, which is shown at the bottom of the Single the Single Core Cable Type dialog. Type dialog. In our example, example, this value corresponds corresponds to “80 mm”. Then, for a trefoil trefoil arrangement, arrangement, it can be proven that the distance distance from the center of the trefoil arrangement to the center of each single core cable is as follows: Ri =

ri √

(1)

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Where Cable .

Ri is

the radius of the trefoil arrangement and

ri is


the radius of the Single Core

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Figure 3.13: Ri and ri layout definition definition • Enter the followi following ng values in the Polar the Polar Coordinates of Line Circuits field: field: Magnit Magn itud ude e1 0.0462

Magnit Magn itud ude e2 0.0462

Magni agnitu tude de 3 0.0462

Angle ngle 1 90

Angle ngle 2 210

Angl Angle e3 330

Table 3.5: Polar coordinates • Now, Now, for the bedding, armour and serving layers, layers, we will include include this information information in the Thickness and and Insulation Thickness of Thickness of the pipe. pipe. Inp Input ut 7.0 mm for the Thickness the Thickness of of the pipe, corresponding to the “Armour” and 6.0 mm for the Insulation the Insulation Thickness , corresponding to the “Bedding” plus “Serving” layers. • Define Define the Depth the Depth to to be 0.4 0.4 m. The The Outer Radius should should be defined as 0.1035 m, since the outer diameter of the cable is 207 mm from the vendor data. • For the rest of the parameters parameters to the right, please input the following: following: Parameter Resistivity Rel. Permeability Fill: Rel. Permi rmittivity Ins. Rel. Permi rmittivity

Value 13.8 uOhm*cm 1 2.3 2.3

Table 3.6: Pipe parameters • Check Check the Reduced the Reduced box box and press Calculate press Calculate.. This will output the electrical electrical values of our new cable. Leave it unchecked, press Calculate press Calculate and and press OK press OK.. Note: Keep in mind that the Reduced Reduced option actually bond the sheaths and armours of the cable, resulting on a reduced element matrix.

Now we have to compare the nominal values of the cable from the vendor data with the matrix output values from PowerFactory from PowerFactory .. The vendor electrical parameters of the cable are as follows: Cable Modelling Tutorial (DIgSILENT (DIgSILENT T Technical Documentation)

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Bondin Bonding g of cables cables in PowerFactory in PowerFactory

Parameter Conductor R DC at 20° 20°C Cable able Indu Induct ctan ance ce Cabl Ca ble e Ca Capa paci cita tanc nce e

Vendor Data PowerFactory Data 0.02 0.0283 83 Ohm/ Ohm/km km 0.02 0.0237 375 5 Ohm/ Ohm/km km 0.09 0.0913 13 Ohm/ Ohm/km km 0.09 0.0962 62 Ohm/ Ohm/k km 60.6 60.632 3274 74 uS/k uS/km m 62.4 62.467 676 6 uS/k uS/km m

Table 3.7: Pipe parameters

We can see that the inductance and capacitance values are consistent with the vendor data. For the resistance value, the difference is due to the definition of the resistance per length in the Single Core Cable Type dialog. Type dialog. To change this value do the following: • Access Access to the the Single Core Cable Type dialog. Type dialog. You can do this by double clicking clicking on the line element, or accessing the filter tool at the icon toolbar in PowerFactory . PowerFactory . See figur figure e below.

Figure 3.14: Access to the Single Core Cable Type dialog • In the Conducting Layers field Layers field,, click click on the blac black k right right pointi pointing ng arrow arrow and select DC- Resistance in Ohm/km . Press OK Press OK.. • Chang Change e the value value of the DC-Resistance DC-Resistance of the conductor to 0.0283 Ohm/km. Ohm/km. Press OK Press OK..

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Bond Bondin ing g of ca cabl bles es in PowerFactory

This section will describe how to define an independent modelling of the cable between sheaths and cores and the subsequent subsequent bonding between them. This is useful useful for monitoring monitoring the current current that is flowing through the sheaths against different types of bonding. Note: Please import the project file ”Cable Tutorial 2.pfd” to PowerFactory and PowerFactory and activate it.

4.1 Cable Cable System System defini definitio tion n First, we begin defining our Cable our Cable System that System that will take into account the coupling between the core and the sheath of our cable. • Define the default default voltage level level fo new elements to be 66 kV. kV. This has to be changed in the toolbar. • Insert two new terminals parallel to the existing existing ones. Name them “Sheath A” and “Sheath B” respectively. • Conne Connect ct a line element between between both terminals. terminals. Name it “Sheath”. “Sheath”. • Hold Hold the the Ctrl key Ctrl key and select the predefined cable and the new created line element. Cable Modelling Tutorial (DIgSILENT (DIgSILENT T Technical Documentation)

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• Right click click on the selection selection and select Define select Define → Cab Cable le System System.. . . . See figure.

Figure 4.1: Cable System definition • A new dialog appears. appears. Select Select the highlighted Cable Cable Definition Definition and press OK press OK.. • Now select select the line element which which will represent represent the core of our cable (Single (Single Core Cable A) and press OK press OK.. • The Cable The Cable System dialog dialog will pop-up. This element assigns the coupling between the core and the sheath of our cable. cable. Press OK Press OK.. • Chang Change e the length of both line elements (core (core and sheath) to be 30 km. • Run a Unbalanced Load Flow calculation Flow calculation and check if the value for the current flowing through the sheath is zero. • Observe that the terminals now have a voltage voltage value. This represents the induced voltage in the sheaths of our cable due to the definition of the coupling system.

4.2 4.2

Bond Bondin ing g

As you can see, no bonding has been defined yet. By means of earthing one or both busbars for the sheath element, we can reduce the voltage against an increased flow of current through the sheaths. The process of earthing one or both busbars busbars is known known as the single bonding or double bonding configurati configuration on respectively respectively.. Normally Normally, for high loaded cables a cross-bondi cross-bonding ng is used. This will reduce furthermore the current current flowing flowing through the sheaths sheaths whilst keeping the voltages voltages at both sides of the sheaths equal to ground potential. To define a cross-bonding configuration, please do the following: • Edit the Cable Definition . You can quick quickly ly access access to this this object object by means of using using the Edit Relevant Objects for Calculation Calculation button in the PowerFactory toolbar PowerFactory toolbar and clicking in the Cable the Cable Definition icon. icon. • Edit the highligh highlighted ted Cable Cable Definition from from the Object the Object Filter . • Check Check the box box Cross Bonded of Bonded of the Circuit the Circuit 1 row. 1 row. Click OK Click OK.. • Now Now run again again a Unbalanced a Unbalanced Load Flow calculation calculation and observe that the current flowing through the sheaths has been reduced.


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References [1] Anders, Anders, G., “Rating “Rating of Electrical Electrical Power Power Cables: Cables: Ampacity Ampacity Computation Computations s for Transm Transmissio ission, n, Distribution, and Industrial Applications”, IEEE Press, 1997. [2] “XLPE Land Cable Systems User´s Guide”, ABB, rev. 5.


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Digsilent-Cable-Tutorial.pdf

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