## 11. Electrical calculation of distribution networks. How to calculate voltage drops in the power line and the load on the transformer ?

One of the mandatory elements of the design is choice of the cross-sectional area of ​​the power line wire. Thus, the designer must perform electrical calculation of the network. An online service for designing external distribution networks SiCAD makes possible to automate the process of electrical calculations.

The principle of calculation is follows:

1. Build a plan for a 0.4 kV low voltage electrical network
2. Specify the location of electricity consumers and power supply (power point) and its wattage capacity
3. Start the calculation process in the main menu item “Calculations / Currents and voltage drop calculation”. Choose the electrical network you need.

The calculation of powers in each span is carried out according to standart DBN B2.5-23 2010 in accordance with the values of capacities (entered by you) in typical nodes of subscriber sets. It should be noted that the typical nodes of the subscriber sets will be considered connected to lines, in the layer with which they are. This takes into account all possible cases of combinations of different types of homes, factories and the presence of electric heating. Electric heating power is taken into account with a diversity factor equal to one, as required by the DBN. After calculating the electric power and currents, voltage drop in each span are calculated. Active and reactive resistivity of cables cores and wires is known. The sum of the voltage drops in each span will be the value of the voltage drop on the way from the power supply to the most remote subscriber. The voltage drops are calculated from the value of the voltage on the busbars of the transformer introduced in the properties of the power supply (Transformer substation). The conclusion of the Institute of Electrodynamics of the National Academy of Sciences of Ukraine on the correctness of the results of electrical calculations in the SiCAD service is positive and you can read it at the link.

To obtain the results of electrical calculations, select “Calculation / Currents and voltage drop calculation” in the main menu and press on any object of the 0.4 kV electricity network. At the same time, no line with a wire for 10, 20 or 35 kV networks should be connected to the 0.4 kV electrical network. The SiCAD service performs verification and does not allow the creation of networks with two power supplies or networks with closed circuits. The result of the calculation will be displayed in a separate modal window – this allows you to simultaneously analyze the result of the calculation and view the project. On the separate tabs displayed the following information:

• Voltage drop dU, percentage voltage drops and voltage deviations from the nominal value for the most remote subscribers.
• Estimated current in Amperes for each power line span.
• Single-phase Short circuits current in connection points of the most remote subscribers of electric power.
• Source load where the total load on the transformer is displayed. Number and types of electricity consumers. Including the types of the user’s own homes with electric heating, if it was introduced when creating the type of house. Below is the result of the calculation for each individual line that departs from the power supply (transformer substation).
• The tab Detailed calculation shows the results of the calculation of electrical parameters for each span of the line.