The operation of electrical appliances is impossible without certain network parameters. They consist of many factors. One of them is the resistance of conductors to electric current. Given the cross section when choosing wires or cables, it is necessary to take into account the voltage drop.
Basic concepts
The voltage drop is a value reflected in the change in potential in different parts of the conductor. The current flowing from the source towards the load changes its parameters due to the resistance of the wires, but its direction remains unchanged. You can measure the voltage with a voltmeter:
- two devices at the beginning and end of the line;
- sequential measurement in several places;
- a voltmeter connected in parallel with the cable.
The simplest circuit is a power source, conductor, load. An example would be an incandescent lamp plugged into a 220 V outlet. If you measure the voltage on the lamp with a device, it will be slightly lower. A drop arose on the resistance of the lamp.
The voltage or voltage drop in a circuit section can be calculated using Ohm's law according to the formula U = IRwhere:
- U - electrical voltage (volts);
- I - current strength in the conductor (amperes);
- R - resistance of the circuit or its elements (ohms).
Knowing any two quantities, you can calculate the third. In this case, it is necessary to take into account the type of current - alternating or constant. If the circuit has several parallel connected resistances, the calculation is somewhat more complicated.
Undervoltage result
A common phenomenon is when the input voltage is determined below the established norm. Sagging along the length of the cable occurs due to the passage of high current, which causes an increase in resistance. Also, losses increase on long lines, which is typical for rural areas.
According to the regulations, losses from the transformer to the most remote section should not exceed 9%. The result of the deviation of the parameters from the norm can be as follows:
- malfunction of volatile installations and equipment, lighting;
- failure of electrical appliances at low input voltages;
- torque reduction when starting an electric motor or compressor installation;
- starting current leads to overheating and engine shutdown;
- uneven current load at the beginning of the line and at the remote end;
- lighting devices work in the sun;
- loss of electricity, underutilization of current power.
The characteristics and operating parameters of electrical appliances are changing. For example, due to weak power, the time for heating the water with a boiler increases. Reducing voltage leads to failures in the electronics.
In operating mode, voltage losses in the cable can be up to 5%. This value is acceptable for power industry networks, as high power currents are delivered over long distances. These lines are subject to increased requirements. Therefore, with losses in everyday life, attention should be paid to secondary energy distribution networks.
Reasons for voltage drop
First of all, you need to understand: this is the fault of the electricity supplier or the consumer. Network problems arise for the following reasons:
- wear of power lines;
- insufficient power transformers;
- power imbalance or phase imbalance.
These problems are related to the supplier, it is impossible to solve them yourself. To understand whether the high-voltage lines are working correctly or not, you will have to call the representatives of the energy supply. They will take measurements and draw up a conclusion.
You can make sure that the fault of the fall is not connected with the supplier yourself. First of all, it is worth finding out from the neighbors if they have similar problems. A multimeter is suitable for measuring voltage in everyday life. Its cost is up to 1000 rubles. If the device at the entrance to the apartment shows normal voltage, the cause must be sought in the home network.
Voltage may drop due to the large length of the wiring. When the network length exceeds 100 meters and the cross-section of the conductors is 16 mm, the oscillations will become regular. To correct the situation, you have to change the wiring.
Weak contacts are an additional resistance to current. It does not reach the devices in sufficient quantities. In addition, faulty contacts can cause a short circuit and cause a fire. To normalize the indicators, it is necessary to replace the emergency section of the circuit and burnt contacts.
The culprit may be a wrong connection of wires going from the power lines to the house. Sometimes, contrary to safety requirements, they connect copper wires to aluminum or copper conductors are connected instead of twisted terminals. The terminals and clamps are made of low-quality materials, or their expiration date has expired.
Perhaps the fault lies in the introductory apparatus itself. In this case, it should be replaced.
How to calculate losses
When calculating the electric line, voltage deviations should not exceed the regulated norms. Allowable fluctuations for household single-phase networks are 209–231V, for a three-phase network, the voltage can vary from 361 to 399 V.
Fluctuations in current strength and power consumption leads to a change in voltage in the conductive conductors near the consumer. Therefore, when drawing up the wiring diagram, it is necessary to take into account permissible losses.
There are two wires in a single-phase network, so the voltage drop can be found by the following formula: U = I * R, in turn, R = (r * 2i) / S.
- Where r - resistivity, which is equal to the resistance of the wire, with a cross section of 1 mm2 and a length of 1 m;
- i - designated as the length of the conductor;
- S - cable section.
In a three-phase network, the power on the phase wires cancel each other out, and the length of the neutral conductor is not taken into account, since no current flows through it. If the phase load is uneven, the calculation is performed as for a single-phase network. For long lines, capacitive and inductive reactance are additionally taken into account.
The calculation of the fall can be performed using the online calculator, there are also special tables. They show the permissible current loads for different types of cables. When calculating the cable cross-section, the following data should be taken into account:
- material of manufacture of conductors;
- hidden or open line laying;
- current load;
- environmental conditions.
When current flows through the cable, wire or bus, they are heated. This process changes the physical properties of conductors. Insulation melts, contacts overheat, wire burn out. The reliability and uninterrupted operation of the mains depends on the correct selection of cable.
How to reduce voltage drop and reduce cable loss
It is possible to reduce the number of losses by reducing the resistance over the entire section of the power supply network. Savings are given by the method of re-grounding zero on each support of the power line.
The cost of power supply by a long line, selected according to the allowable voltage drop, is greater than the choice made by heating the cable. Nevertheless, there is an opportunity to reduce these costs.
- Strengthen the initial potential of the power cable by connecting it to a separate transformer.
- You can achieve constant voltage values in the network by installing a stabilizer near the load.
- Consumers with low loads of 12–36 V are connected through a transformer or power supply.
The longer the power line cable, the greater the resistance that occurs when current flows through it. Obviously, the voltage loss is also higher. You can reduce them by combining methods with each other.
- Reduce costs by increasing the cross section of the supply cable. But this method will require large financial investments.
- When developing energy supply lines, you should choose the shortest possible path, since a straight line is always shorter than a broken line.
- With decreasing temperature, the resistance of metals decreases. Vented cable trays and other designs reduce line loss.
- Reducing the load is possible if there are many power sources and consumers.
Savings are provided by proper maintenance and prevention of power networks - checking the density and strength of contacts, using reliable terminal blocks.
It is necessary to approach the issue of energy conservation with full responsibility. The problem of voltage loss can disable expensive appliances, tools. Do not neglect security measures, they will neutralize power surges and protect household appliances and equipment in the enterprise.
