Dimensioning of a cluster
- Landis+Gyr – EV Editor 4
- Andrej Zadravec (Deactivated)
- Denis Leskovar
Table of Contents
- 1 Table of Contents
- 2 4. Dimensioning of a cluster
- 2.1 Cabling Route for the Connection of Multiple Charging Stations
- 2.2 Cluster Cables Cross-Section
- 2.2.1.1 Continuous operating current
- 2.2.1.2 Voltage drop
- 2.2.1.3 Short circuit withstand
- 2.2.2 Examples of Connection
- 2.2.2.1 Case 1: Power Cables for Cluster of 15 INCH DUO in Expanded Star Network
- 2.2.2.2 Case 2: Power Cables for Cluster of 15 INCH DUO in Expanded Point to Point Network
- 2.2.2.3 Case 3: Power Cables for Cluster of 15 INCH DUO in Expanded Point to Point Network
- 2.2.2.4 Calculation of total voltage drop
4. Dimensioning of a cluster
When selecting the cluster configuration and cluster master it is important to know that with INCH Duo can handle power management of up to 36 electric vehicles. This is valid for the most unfavourable scenario with low power capacity available, meaning constant need for power management recalculations with inclusion of data obtained from Load Guard. INCH Duo could also control larger clusters, depending on the individual case.
Larger cluster (supply of up to 300 electric vehicles in most unfavourable scenario) is possible with use of industrial computer and connection to Etrel Ocean management software.
Main decision factor in cluster configuration is usually the available charging power at the location. Cluster of charging stations can be planned and configured to allow charging with maximal power to all connected vehicles. Another option is to plan to the limitation of capacity intended for charging and to maximal charging current of the cluster.
When a larger number of parking spots need to be covered with charging stations, the general proposal is to have a dedicated parking spot for each charging connector that can offer at least charging with minimum current of 6 A to connected electric vehicle.
For example:
Five INCH DUO charging stations can be configured to be able to charge with maximal charging current of 32 A per phase, per each charging spot. Five INCH DUO charging stations have 10 charging spots, with maximal charging current of 320 A per phase, meaning that maximal charging power is 220,8 kW.
Five INCH DUO charging stations can also be configured to be able to charge only with minimal charging current of 6 A per phase. These five INCH DUO charging stations will have maximal charging current of 60 A per phase, meaning that maximal charging power is 41,4 kW.
Normally the cluster is dimensioned for available power and power management limits the total current of the cluster to allowable levels. Also, possible future upgrades should be considered and could lead to decision to install cables with larger cross-sections.
In case of very large clusters and long distances, possible dedicated power transformers could be needed to provide low enough voltage drop.
Cabling Route for the Connection of Multiple Charging Stations
Charging station can be installed independently or combined in connection with other stations (the so-called clustering of charging stations).
When multiple charging stations are installed in a single area, the power supply cables can be routed in several different ways. The physical connection of a group of charging stations can be different than the setting of software grouping.
It is recommended, that the charging stations logically belonging to one cluster are also physically connected to the same cluster with common point of power supply.
The main reason would be possible power management of the cluster and limitation of charging power on basis of set and measured data. Also, avoidance of possible confusion during the maintenance or troubleshooting.
Cluster can be defined only on level of charging stations where one charging station is designated as cluster master. They can also be managed from charging infrastructure management system.
Power Cables Star network topology
Power cables of the charging stations are connected to the common point (electrical cabinet in the following figure).
Figure 7: Cluster cabling route for multiple charging stations - star network topology
Power cables Point to Point Network Topology
Power cables are routed to the first station, which is then connected to the next station with a separate power cable and a separate communication cable. Each additional station is then connected in the same way with its preceding station.
In case that Point-to-Point communication is needed for the power supply, all INCH Duo’s of the cluster with exclusion of the last one, should be equipped with double terminal clamps.
Figure 8: Cluster cabling route - point to point network topology (daisy chain)
Power cables Hybrid Network Topology
When considering large clusters, the power supply network topology will most often be a hybrid of star and point to point network topology.
Communication
Although charging without network connection is possible, to enable common charging scenarios, network connection is required. Larger clusters are usually also connected to control centre, enabling remote control and management.
Cluster of charging stations can be connected to the network with UTP cable or over Wi-Fi to the existing ethernet network, or ethernet network can be created only for the charging stations.
One of the charging stations is designated as a cluster master and represents one point of management for the complete cluster.
All the charging stations of the cluster need to be connected to the network. The communication cables should follow star network topology. Point-to-Point wiring of communication cables is not fully supported yet. When needed all INCH Duo’s of the cluster should be equipped with router.
Table 6: Power cables installation method
A1 - Insulated single core conductors in conduit in a thermally insulated wall A2 - Multicore cable in conduit in a thermally insulated wall This method also applies to single core or multicore cables installed directly in a thermally insulated wall (use methods A1 and A2 respectively), conductors installed in mouldings, architraves, and window frames.
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B1 - Insulated single core conductors in conduit on a wall B2 - Multicore cable in conduit on a wall This method applies when a conduit is installed inside a wall, against a wall or spaced less than 0.3 x D (overall diameter of the cable) from the wall. Method B also applies for cables installed in trunking / cable duct against a wall or suspended from a wall and cables installed in building cavities.
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C - Single core or multi-core cable on a wooden wall This method also applies to cables fixed directly to walls or ceilings, suspended from ceilings, installed on unperforated cable trays (run horizontally or vertically), and installed directly in a masonry wall (with thermal resistivity less than 2 K·m/W).
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D1 - Multicore or single core cables installed in conduit buried in the ground D2 - Multicore or single core cables buried directly in the ground | |
E - Multicore cable in free-air This method applies to cables installed on cable ladder, perforated cable tray or cleats provided that the cable is spaced more than 0.3 x D (overall diameter of the cable) from the wall. Note that cables installed on unperforated cable trays are classified under Method C.
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F - Single core cables touching in free-air This method applies to cables installed on cable ladder, perforated cable tray or cleats provided that the cable is spaced more than 0.3 x D (overall diameter of the cable) from the wall. Note that cables installed on unperforated cable trays are classified under Method C.
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G - Single-core cables laid flat and spaced in free-air This method applies to cables installed on cable ladder, perforated cable tray or cleats provided that the cable is spaced more than 0.3 x D (overall diameter of the cable) from the wall and with at least 1 x D spacings between cables. Note that cables installed on unperforated cable trays are classified under Method C. This method also applies to cables installed in air supported by insulators. |
Cluster Cables Cross-Section
When INCH DUO is designated as cluster master, it is possible to connect 18 INCH DUO charging stations to this cluster, meaning that charging is supported to 36 electric vehicles simultaneously. If industrial computer is designated as cluster master, it is possible to connect 150 INCH DUO charging stations in the same cluster, meaning that charging is supported to 300 electric vehicles simultaneously.
Considering maximal charging current of Mode 3 AC conductive charging point of 32 A (three-phase), the maximal charging power is 22,08 kW, meaning 44,16 kW for one INCH Duo. In large clusters this number rise significantly and can be in a range of large industrial consumers.
The currents presented in the following table require additional considerations from the electrical works planning view, which should be determined in the electrical project. It is possible, that high charging current would require implementation of bus-bar systems and/or possible installation of power transformers and/or additional requirements from the view of electrical safety and documentation preparation.
Table 7: Considering maximal current in case of clusters
Number of INCH DUO | Number of electric vehicles | Max. charging current (per phase) | Maximal charging power |
5 | 10 | 320 A | 220,8 kW |
10 | 20 | 640 A | 441,6 kW |
15 | 30 | 960 A | 662,4 kW |
20 | 40 | 1280 A | 883,2 kW |
25 | 50 | 1600 A | 1104 kW |
30 | 60 | 1920 A | 1324,8 kW |
Main factor influencing the design of a cluster is the available charging power at the location of cluster installation. This limitation can also be expressed as maximal current.
When considering charging with full power the available capacity can quickly run out even with small numbers of simultaneously charged vehicles. INCH DUO has implemented power management functionalities with option of software limitation of maximal current of charging for individual charging station or for complete cluster.
Almost all vehicles require minimally 6 A of charging current. Considering that there are some vehicles that require higher minimal charging current, some reserve to the numbers in the following table should be added to ensure all connected vehicles can charge simultaneously.
Table 8: Considering minimal current in case of clusters (three-phase wiring)
Number of INCH DUO | Number of electric vehicles | Min. charging current (per phase) | Maximal charging power |
5 | 10 | 60 A | 41,4 kW |
10 | 20 | 120 A | 82,8 kW |
15 | 30 | 180 A | 124,2 kW |
20 | 40 | 240 A | 165,6 kW |
25 | 50 | 300 A | 207 kW |
30 | 60 | 360 A | 248,4 kW |
In the previous table the numbers of minimal charging current are presented. Such system allows charging of individual electric vehicles with maximal power of 22,08 kW.
Power management can be used to set limitation of the maximal current of the complete cluster (determined by the location, e.g., main fuses). If this limitation is active, individual charging stations limit the charging power of the connected vehicles.
Considering that there are some vehicles that require higher minimal charging current, some reserve to the numbers in the following table should be added to ensure all connected vehicles can charge simultaneously.
All presented values are only indicative and are not a substitution for exact calculation of required cross-sections. Specified voltage drops are considering only voltage drop in a cable of defined cross-section and for specified current.
When calculating complete voltage drop of installation, the lowering of voltage across all the elements of the current path should be taken into consideration.
Continuous operating current
Determining the right cross-section of conductors, the method of installation need to be considered. Additional consideration is the material of the conductor and material of its isolation. The real current must also be determined using the selected planning temperature.
Informational values of minimal cables cross-section were selected using the following:
Three-phase system with copper conductors with XLPE insulation
Ambient temperature 35 °C
Ground temperature 25 °C
Thermal resistivity of the soil 2,5 K·m/W
Table 9: Minimal cables cross-sections under specified conditions (1/2)
Current of the cluster | [A] | 32 | 64 | 96 | 128 | 160 | 192 | 224 |
Method of installation | A1 [mm] | 6 | 16 | 35 | 50 | 70 | 95 | 120 |
Method of installation | A2 [mm] | 6 | 16 | 35 | 70 | 95 | 120 | 150 |
Method of installation | B1 [mm] | 4 | 16 | 25 | 35 | 50 | 70 | 95 |
Method of installation | B2 [mm] | 4 | 16 | 25 | 50 | 70 | 95 | 120 |
Method of installation | C [mm] | 4 | 10 | 25 | 35 | 50 | 70 | 95 |
Method of installation | D1 [mm] | 4 | 16 | 35 | 50 | 70 | 120 | 150 |
Method of installation | D2 [mm] | 4 | 16 | 25 | 50 | 70 | 95 | 120 |
Method of installation | E [mm] | 2,5 | 10 | 16 | 25 | 35 | 50 | 70 |
Method of installation | F [mm] | 25 | 25 | 25 | 25 | 35 | 50 | 50 |
Method of installation | G [mm] | 25 | 25 | 25 | 25 | 25 | 35 | 50 |
Table 10: Minimal cables cross-sections under specified conditions (2/2)
Current of the cluster | [A] | 256 | 288 | 320 | 352 | 384 | 416 | 448 |
Method of installation | A1 [mm] | 150 | 185 | 240 | 240 | 300 | 300 | X |
Method of installation | A2 [mm] | 185 | 240 | 240 | 300 | X | X | X |
Method of installation | B1 [mm] | 95 | 120 | 150 | 185 | 240 | 240 | 300 |
Method of installation | B2 [mm] | 120 | 185 | 185 | 240 | 300 | 300 | X |
Method of installation | C [mm] | 95 | 120 | 150 | 150 | 185 | 240 | 240 |
Method of installation | D1 [mm] | 185 | 240 | 300 | X | X | X | X |
Method of installation | D2 [mm] | 150 | 185 | 240 | 240 | 300 | X | X |
Method of installation | E [mm] | 70 | 95 | 95 | 120 | 120 | 150 | 150 |
Method of installation | F [mm] | 70 | 70 | 95 | 95 | 120 | 150 | 150 |
Method of installation | G [mm] | 50 | 70 | 70 | 95 | 95 | 120 | 120 |
Voltage drop
The requirement for the maximum voltage drop of the installation can be different across different countries. Usually, it is required that the voltage drop of the installation is below 4 % (or in some cases below 5 %).
The length of the conductors and charging current are major factors determining the adequacy of cables cross-section, however voltage drop occurs on other components or devices as well. Because of it, some reserve should be considered when selecting cables cross-section.
In large clusters of charging stations also the distances can be large. Because of it the voltage drop in the cables can be determining factor choosing the cables cross-section and configuration of the cluster.
Voltage drop in the power cable is proportional to the current of the load. When installing two INCH DUO charging stations, also voltage drops are twice as high as in case of one INCH DUO without considering any additional elements.
Figure 9: Cluster cabling route length
The voltage drop presented in the tables are calculated for single-phase and three-phase connection. Although the connection of INCH DUO is almost always three-phase, using values of voltage drop in single-phase can represent beneficial reserve when planning the correct cable cross-section.
Table 11: Voltage drop in conductors with 35 mm2 cable cross-section and charging current of 128 A.
Charging current 128 A (Two INCH DUO with max. current) | Conductor 35 mm2 Single phase | Conductor 35 mm2 Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
40 | 2,62 | 2,27 |
50 | 3,28 | 2,84 |
60 | 3,93 | 3,40 |
Table 12: Voltage drop in conductors with 50 mm2 cable cross-section and charging current of 128 A.
Charging current 128 A (Two INCH DUO with max. current) | Conductor 50 mm2 Single phase | Conductor 50 mm2 Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
60 | 2,84 | 2,46 |
70 | 3,31 | 2,87 |
80 | 3,78 | 3,27 |
90 | 4,25 | 3,68 |
For example, looking at the table determining minimal cross-section of cables for maximal continuous current of 320 A, depending on the installation method, either 70 mm2 (Method G) or 150 mm2 (Method C) cables could be used when connecting 5 INCH DUO charging stations with maximum charging current available. Reviewing the selection of the cable with consideration of voltage drop, shows that allowable distance of conductors is a lot lower than if selecting higher cable cross-section.
Table 13: Voltage drop in conductors with 70 mm2 cable cross-section and charging current of 320 A.
Charging current 320 A (Five INCH DUO with max. current) | Conductor 70 mm2 Single phase | Conductor 70 mm2 Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
40 | 3,51 | 3,04 |
50 | 4,39 | 3,80 |
Table 14: Voltage drop in conductors with 95 mm2 cable cross-section and charging current of 320 A.
Charging current 320 A (Five INCH DUO with max. current) | Conductor 95 mm2 Single phase | Conductor 95 mm2 Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
30 | 2,03 | 1,76 |
40 | 2,71 | 2,35 |
50 | 3,39 | 2,93 |
60 | 4,06 | 3,52 |
Table 15: Voltage drop in conductors with 120 mm2 cable cross-section and charging current of 320 A.
Charging current 320 A (Five INCH DUO with max. current) | Conductor 120 mm2 Single phase | Conductor 120 mm2 Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
50 | 2,80 | 2,43 |
60 | 3,36 | 2,91 |
70 | 3,93 | 3,40 |
80 | 4,49 | 3,88 |
Table 16: Voltage drop in conductors with 150 mm2 cable cross-section and charging current of 320 A.
Charging current 320 A (Five INCH DUO with max. current) | Conductor 150 mm2 Single phase | Conductor 150 mm2 Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
40 | 1,89 | 1,64 |
50 | 2,36 | 2,04 |
60 | 2,83 | 2,45 |
70 | 3,30 | 2,86 |
80 | 3,78 | 3,27 |
90 | 4,25 | 3,68 |
Table 17: Voltage drop in conductors with 240 mm2 cable cross-section and charging current of 320 A.
Charging current 320 A (Five INCH DUO with max. current) | Conductor 240 mm2 Single phase | Conductor 150 mm2 Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
80 | 2,71 | 2,35 |
90 | 3,05 | 2,64 |
100 | 3,39 | 2,94 |
110 | 3,73 | 3,23 |
120 | 4,07 | 3,52 |
Table 18: Voltage drop in conductors with 300 mm2 cable cross-section and charging current of 320 A.
Charging current 320 A (Five INCH DUO with max. current) | Conductor 300 mm2 Single phase | Conductor 300 mm2 Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
100 | 2,95 | 2,55 |
110 | 3,24 | 2,81 |
120 | 3,54 | 3,06 |
130 | 3,83 | 3,32 |
140 | 4,13 | 3,57 |
There are several options considering larger distances of cable path and larger charging currents. The main conductor could have larger cross-section, that could be distributed through junction boxes, each connecting small cluster. The use of busbar trunking systems could be beneficial.
Short circuit withstand
Although the short circuit withstand criterion must be evaluated when dimensioning cables cross-section, in practice requirements of the first two criteria are stricter (continuous operating current and voltage drop).
Table 19: Minimum cable cross-section able to withstand specified short circuit
Short circuit | Initial temperature 65 ° C | Initial temperature 35 ° C | ||
XLPE, copper | PVC, copper | XLPE, copper | PVC, copper | |
2 kA, 10 ms | 1,28 mm2 | 1,69 mm2 | 1,16 mm2 | 1,43 mm2 |
2 kA, 20 ms | 1,81 mm2 | 2,39 mm2 | 1,63 mm2 | 2,03 mm2 |
3 kA, 10 ms | 1,91 mm2 | 2,53 mm2 | 1,73 mm2 | 2,15 mm2 |
3 kA, 20 ms | 2,71 mm2 | 3,58 mm2 | 2,45 mm2 | 3,04 mm2 |
5 kA, 10 ms | 3,19 mm2 | 4,22 mm2 | 2,89 mm2 | 3,58 mm2 |
5 kA, 20 ms | 4,51 mm2 | 5,96 mm2 | 4,09 mm2 | 5,07 mm2 |
Examples of Connection
Case 1: Power Cables for Cluster of 15 INCH DUO in Expanded Star Network
The case presented in the following figure is possible with normal configuration of INCH DUO. The cable cross-sections must be determined in accordance with all three criteria.
The distances are depending on the arrangement of parking spots and available space. One, two or more levels of electrical junction boxes could be used. On the figure two levels are presented and the first could be omitted (the grey box on the left).
Keep in mind that if the cables cross-section changes (e.g., in first junction box, from cross-section used on L1 to cross-section used on L2) and is lowered to level that cannot sustain the full current, the over-current protection element should be installed.
Figure 10: Example of INCH DUO connection – standard configuration
Maximal continuous current of the cluster
Maximal operating current of the presented case is 960 A. Cables supporting this current would need to be installed in E, F or G method of installation or a bus-bar system could be used. For cables used at L1, the cross-sections would need to be:
Method of installation E: 400 mm2
Method of installation F: 500 mm2
Method of installation G: 400 mm2
Such a high requirement indicates the possibility of using three main power lines to separate groups of the cluster, each designed for 320 A. These cables selection is the same as on the presented figure at L2 and L3 and L4, where the maximal operating current is 320 A. Cables used at L2, L3 or L4 would need to have cross-sections of at least:
Method of installation A1: 240 mm2
Method of installation A2: 240 mm2
Method of installation B1: 150 mm2
Method of installation B2: 185 mm2
Method of installation C: 150 mm2
Method of installation D1: 300 mm2
Method of installation D2: 240 mm2
Method of installation E: 95 mm2
Method of installation F: 95 mm2
Method of installation G: 70 mm2
Cables from the 2nd level junction boxes to individual charging stations need to be dimensioned for 64 A, meaning minimum cross-section of 10 mm2.
Voltage drop
Voltage drop in cable at L1
Table 20: Voltage drop in conductors with 400 mm2 cable cross-section and charging current of 960 A.
Charging current | Conductor | Conductor |
960 A | 400 mm2 | 400 mm2 |
| Single phase | Three phase |
Distance [m] | Voltage drop [%] | Voltage drop [%] |
10 | 0,75 | 0,65 |
20 | 1,50 | 1,30 |
30 | 2,25 | 1,95 |
40 | 3,00 | 2,60 |
50 | 3,75 | 3,25 |
60 | 4,51 | 3,90 |
For 960 A and copper conductors with cross-section of 400 mm2, the voltage drop is quite large, indicating the possible need of more main power cable routes or need for limitation of maximal charging current.
Voltage drop in cable at L2 (L3, L4)
Please check values of voltage drop according to distance and cable cross-section in tables 11-18.
Voltage drop in cable of charging station connection
Please check values of voltage drop according to distance and cable cross-section in tables 2-5.
Case 2: Power Cables for Cluster of 15 INCH DUO in Expanded Point to Point Network
The case presented in the following figure is possible only with double clamp terminals installed in all INCH DUO charging stations, instead of the last one of the power lines (three INCH DUOs that are completely right on the figure). The cable cross-sections must be determined in accordance with all three criteria.
Figure 11: Example of INCH DUO connection – use of double terminal clamps
Maximal continuous current of the cluster
Maximal operating current of the presented case is 960 A. Cables supporting this current would need to be installed in E, F or G method of installation or a busbar trunking system could be used. For cables used at L1, the cross-sections would need to be:
Method of installation E: 400 mm2
Method of installation F: 500 mm2
Method of installation G: 400 mm2
Such a high requirement indicates the possibility of using three main power lines to separate groups of the cluster, each designed for 320 A. These cables selection is the same as on the presented figure at L2 and L3 and L4, where the maximal operating current is 320 A. Cables used at L2, L3 or L4 would need to have cross-sections of at least:
Method of installation A1: 240 mm2
Method of installation A2: 240 mm2
Method of installation B1: 150 mm2
Method of installation B2: 185 mm2
Method of installation C: 150 mm2
Method of installation D1: 300 mm2
Method of installation D2: 240 mm2
Method of installation E: 95 mm2
Method of installation F: 95 mm2
Method of installation G: 70 mm2
Voltage drop
The length of L1 is the decisive factor. Table 20 shows that practical maximal length of this cable with cross-section of 400 mm2 is around 10 - 30 m (considering reserve, because voltage drop occurs on all elements).
There are three possible main obstacles:
At L1 the cable cross-section is extremely large indicating the possible need to use e.g., three main power lines, each connecting 5 x INCH DUO as shown on the following figure.
At L2, L3 and L4 the cables are relatively large. Because of the point-to-point network configuration of five INCH DUOs, the cables should not exceed 95 mm2, to be able to use additional double terminal clamps inside all INCH DUO units, except in the last one. If larger cables cross-section is needed, the double terminal clamps are too large to fit inside INCH DUO and the connection would be possible with use of additional junction boxes in front of every INCH DUO except the last.
It is very likely that dedicated transformer will be required to connect 15 or more INCH DUO charging station, or the total charging current of the cluster will need to be limited.
Case 3: Power Cables for Cluster of 15 INCH DUO in Expanded Point to Point Network
Figure 12: Example of INCH DUO connection – use of double terminal clamps
The figure presented above is showing possible selected configuration, after reviewing Case 1 and 2. It could be more expensive to install three main routes of cables, however using more conductive material (copper) will lower the voltage drop of installation (and with it the power losses).
Calculation of total voltage drop
The presented tables include only values of voltage drops in the cables. Voltage drops occur on all elements of electrical system and not only in cables and this should be evaluated or enough reserve when selecting cables cross-section is needed.
The distances play a major role when selecting cluster configuration.
When installing larger number of charging stations, the electrical project of such high power and currents needs to be prepared by licensed electrical designer.
Warning! Before installing, wiring, handling or accessing the charging station in any way, make sure to read, understand and follow the Safety Guidelines.
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