When calculating the voltage drop in a cable, it is important to consider its length, cross-sectional areas, inductive resistance, connection of wires. With this reference information, you can make your own voltage drop calculations.
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Types and structure of losses
Even the most efficient power supply systems have some kind of actual power losses. Losses are defined as the difference between the electricity given to users and the electricity actually delivered to them. This is due to the imperfection of the systems and the physical properties of the materials from which they are made.
The most common type of power loss in electrical networks is related to voltage loss from cable length. In order to normalize the financial costs and calculate their actual value, such a classification has been developed:
- Technical factor. It is related to the characteristics of physical processes and may vary under the influence of loads, conditional fixed costs and climatic circumstances.
- The cost of using additional supplies and providing the right conditions for the activities of technical personnel.
- Commercial factor. This group includes deviations due to imperfection of control and measuring devices and other things that provoke underestimation of electric energy.
The main causes of voltage loss
The main cause of power loss in the cable is losses in the power lines. The distance from the power plant to the consumers not only dissipates power, but also the voltage drops (which, if it reaches less than the minimum allowable value, can provoke not only inefficient operation of devices, but even their complete inoperability.
Also losses in electrical networks can be caused by the reactive component of the electrical circuit section, i.e. the presence in these sections of any inductive elements (these may be communication and loop coils, transformers, low and high frequency chokes, electric motors).
Ways to reduce losses in electrical networks
The user of the network can not affect the losses in the power line, but can reduce the voltage drop in a section of the circuit by wiring its elements competently.
It is better to connect copper cable to copper cable and aluminum cable to aluminum cable. The number of connections of wires, where the material of the core changes, it is better to reduce to a minimum, as in such places not only dissipates energy, but also increases heat generation, which at an insufficient level of thermal insulation can be fire hazardous. Given the specific conductivity and resistivity values of copper and aluminum, it is more energy efficient to use copper.
If possible, when planning an electrical circuit, any inductive elements such as coils (L), transformers and motors are better connected in parallel, because according to the laws of physics, the total inductance of such a circuit is reduced, while in series connection, on the contrary, increases.
To smooth out the reactive component, capacitor units (or RC-filters combined with resistors) are also used.
Depending on how the capacitors and the consumer are connected, there are several types of compensation: personal, group and general.
- In personal compensation the capacitance is connected directly to the point where reactive power occurs, i.e. own capacitor to an induction motor, one more to a discharge lamp, one more to a welding lamp, one more for a transformer, etc. At this point the incoming cables are relieved of reactive currents to the individual user.
- Group compensation involves connecting one or more capacitors to several elements with large inductive characteristics. In this situation, the regular simultaneous activity of several users involves the transfer of total reactive energy between loads and capacitors. The line that supplies electrical energy to the group of loads will be unloaded.
- Total compensation involves inserting capacitors with a regulator in the main switchboard, or GRES. It evaluates the current reactive power consumption and quickly connects and disconnects the required number of capacitors. As a result, the total power taken from the network is minimized in accordance with the instantaneous amount of reactive power required.
- All reactive power compensation units consist of a pair of capacitor branches, a pair of stages, which are formed specifically for the electrical network depending on the potential loads. Typical step sizes are 5; 10; 20; 30; 50; 7.5; 12.5; 25 kvar.
To purchase large steps (100 or more kvar) connect in parallel small ones. Grid loads are reduced, switching currents and their interference are reduced. In networks with many high harmonics of the mains voltage, capacitors are protected by chokes.
Automatic compensators provide the network equipped with them with such advantages:
- reduce the load on transformers;
- make it easier to meet cable cross-section requirements;
- make it possible to load the grid more than it would be possible without compensation;
- eliminate the causes of network voltage reduction, even when the load is connected by long cables;
- increase the efficiency of mobile fuel-powered generators;
- make it easier to start electric motors;
- increase the cosine phi;
- eliminate reactive power from circuits;
- protect against overvoltages;
- improve regulation of grid characteristics.
Calculation Calculator for Voltage Loss in Cable
For any cable, voltage loss calculations can be done online. Below is an online voltage cable loss calculator.
The calculator is in development, it will be available soon.
Calculation using the formula
If you want to calculate yourself what the voltage drop in a wire is, taking into account its length and other factors affecting losses, you can use the formula for calculating the voltage drop in a cable:
ΔU, % = (Un - U) * 100 / Un,
where Un is the nominal voltage at the mains input;
U is the voltage at the individual network element (consider the loss as a percentage of the nominal voltage present at the input).
From this we can derive a formula for calculating power losses:
ΔP, % = (Un - U) * I * 100/ Un,
where Un is the nominal voltage at the inlet into the network;
I - actual current of the network;
U - voltage on a single element of the network (consider losses as a percentage of the nominal voltage at the input).
Table of voltage drops by cable length
Below are approximate voltage drops along the cable length (Knoring table). Determine the required cross-section and look up the value in the corresponding column.
| ΔU, % | Load torque for copper conductors, kW∙m, two-wire lines at 220 V | |||||
|---|---|---|---|---|---|---|
| At conductor cross-section s, mm², equal to | ||||||
| 1,5 | 2,5 | 4 | 6 | 10 | 16 | |
| 1 | 18 | 30 | 48 | 72 | 120 | 192 |
| 2 | 36 | 60 | 96 | 144 | 240 | 384 |
| 3 | 54 | 90 | 144 | 216 | 360 | 576 |
| 4 | 72 | 120 | 192 | 288 | 480 | 768 |
| 5 | 90 | 150 | 240 | 360 | 600 | 960 |
Wire conductors emit heat when current flows. The size of the current, together with the resistance of the conductors, determines the degree of loss. If you have data on the resistance of the cable and the amount of current flowing through them, you can find out the amount of loss in the circuit.
The tables do not take into account the inductive resistance, because with wires, it is too small and cannot equal the active resistance.
Who pays for electricity losses
Electricity losses during transmission (if transmitted over long distances) can be substantial. This affects the financial side of the issue. The reactive component is taken into account when determining the total rate of use of nominal current for the population.
For single-phase lines, it is already included in the cost, taking into account the parameters of the network. For legal entities, this component is calculated regardless of the active loads and is indicated separately in the bill provided, at a special rate (cheaper than active). This is done due to the presence of a large number of induction mechanisms (e.g., electric motors) at enterprises.
Energy regulators set the permissible voltage drop, or the standard for losses in electric grids. The user pays for transmission losses. Therefore, from the consumer's point of view, it is economically advantageous to consider reducing them by changing the characteristics of the electrical circuit.
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