Seven Ways to Combat Losses in Aerial Power Networks

The causes of energy losses in overhead lines and ways to deal with them, based on practical experience.

Probably, everyone who has a house in the village, lives in the private sector in the city or builds his own house, over time, will face the problem of instability of the electricity network. This is expressed in sharp surges, problems of protection of electrical appliances during thunderstorms, long periods of very high or very low voltage in the mains.

Many of these problems are associated with the features of overhead electric lines, others, with the failure to comply with the elementary rules for laying lines and their maintenance. Unfortunately, in our country, the slogan: "Saving the drowning people is the work of the drowning people themselves" is being increasingly implemented. Therefore, we will try to consider these problems and how to solve them in more detail.

Where do the losses come from in electrical networks?

Ohm is to blame.

For those who are familiar with Ohm's law, it is not difficult to remember that U = I * R. This means that the voltage drop in the wires of the power line is proportional to its resistance and the current through it. The more this drop, the less the voltage in the outlets in your home. Therefore, the resistance of the power line must be reduced. Moreover, its resistance consists of the resistance of the direct and return wires - phase and zero from the transformer of the substation to your home.

Incomprehensible reactive power.

The second source of loss is reactive power or rather reactive load. If the load is purely active, for example, incandescent lamps, electric heaters, electric stoves, then the energy is consumed almost completely (more than 90% efficiency, cos tends to 1). But this is an ideal case, usually the load is capacitive or inductive. Really cosine phi Consumer value is variable over time and has a value from 0.3 to 0.8, unless special measures are applied.

Under reactive loading, there is a phenomenon of incomplete absorption of energy, its reflection from the load and the circulation of stray currents in the wires. This results in additional losses in the wires for heating, voltage and current surges, leading to malfunctions. For example, a partially loaded asynchronous electric motor of a power saw or sawmill has cos 0.3-0.5. In addition to heat loss, in the presence of a powerful reactive load, electricity meters “lie” very much.

It is known from statistics that, due to uncompensated reactive power, a consumer loses up to 30% of electricity. In order to eliminate these types of losses, reactive power compensators. Such devices are commercially available from industry. Moreover, they come from the "single-socket" version, to devices installed on the substation transformer.

Werewolves in sweatshirts.

The third source of losses is the banal theft of electricity. It would seem that law enforcement agencies should deal with this, but they do not have energy audit departments. Therefore, the consumer should also deal with the third source of losses, as according to the law, he must have a common house or general business meter and the whole herd pays for the theft of a black sheep.

Estimation of line losses by a specific example.

Line resistance R = (ρ * L) / S, where ρ is the resistivity of the wire material, L is its length, S is the cross section. For copper, the resistivity is 0.017, and for aluminum, 0.028 Ohm * mm2 / m. Copper has almost two times less losses, but it is much heavier and more expensive than aluminum, so aluminum wires are usually chosen for overhead lines.

Thus, the resistance of one meter of aluminum wire with a cross section of 16 square millimeters will be (0.028 x 1) /16=0.0018 Ohms.Let's see what the losses will be in a line with a length of 500 m, with a load power of 5 kW. Since the current flows through two wires, we double the line length, i.e. 1000 m.

The current strength at a power of 5 kW will be: 5000/220 = 22.7 A. The voltage drop in the line is U = 1000x0.0018x22.7 = 41 V. The voltage at the load is 220-41 = 179 V. This is already less than the allowable 15% voltage drop. At a maximum current of 63 A, for which this wire is designed (14 kW), i.e. when the nearest neighbors turn on their loads, U = 1000x0.0018x63 = 113 V! That is why in my country house in the evenings a light bulb barely glows!

Ways to deal with losses.

The first simplest way to deal with losses.

The first method is based on lower ground wire resistance. As you know, the current flows through two wires: zero and phase. If increasing the cross section of a phase wire is quite expensive (the cost of copper or aluminum plus dismantling and installation work), then the resistance of the neutral wire can be reduced quite simply and very cheaply.

This method has been used from the moment the first power lines were laid, but at present it is often not used because of “indifference” or lack of knowledge. It consists in re-grounding the neutral wire on each pole of the power line or (and) on each load. In this case, the earth resistance between the zero of the substation transformer and the consumer zero is connected in parallel with the resistance of the neutral wire.

If grounding is done correctly, i.e. Since its resistance is less than 8 ohms for a single-phase network, and less than 4 ohms for a three-phase network, it is possible to significantly (up to 50%) reduce losses in the line.

The second simplest way to deal with losses.

The second simplest method is also based on resistance reduction. Only in this case, it is necessary to check both wires - zero and phase. During operation of overhead lines due to wire breakage, places of local resistance increase are formed - twisting, splices, etc. In the process of work in these places there is a local heating and further degradation of the wire, threatening a rupture.

Such places are visible at night due to sparking and glow. It is necessary to periodically visually check the power line and replace its particularly bad segments or the entire line.

For repair it is best to apply self-supporting aluminum insulated SIP cables. They are called self-supporting, because do not require a steel cable for suspension and do not tear under the weight of snow and ice. Such cables are durable (service life more than 25 years), there are special accessories for easy and convenient fastening them to poles and buildings.

The third way to deal with losses.

It is clear that the third way is replacement of the old "air" with a new one.

Cables of types SIP-2A, SIP-3, SIP-4 are on sale. The cable cross-section is chosen at least 16 square millimeters, it can pass current up to 63 A, which corresponds to a power of 14 kW with a single-phase network and 42 kW with a three-phase. The cable has two-layer insulation and is coated with a special plastic that protects the insulation of the wires from solar radiation. Sample prices for SIP can be found here: http://www.eti.su/price/cable/over/over_399.html. A two-wire SIP cable costs from 23 rubles. per linear meter.

The fourth way to deal with losses.

This method is based on the use of special voltage stabilizers at the entrance to the house or other object. Such stabilizers are both single-phase and three-phase type. They increase cos and provide stabilization of the output voltage within + - 5%, with a change in input voltage + - 30%. Their power range can be from hundreds of watts to hundreds of kW.

Here are some sites dedicated to stabilizers. However, we note that due to phase imbalance and losses in the power line, the voltage at the input of the stabilizer can drop below 150 V. In this case, the built-in protection is triggered and you have no choice but to reduce your energy needs.

The fifth way to compensate for electricity losses.

This is the way use of reactive power compensation devices. If the load is inductive, for example, various electric motors, then these are capacitors, if capacitive, then these are special inductances.

The sixth way - the fight against theft of electricity.

According to work experience, the most effective solution is removal electric meter from the building and installing it on a pole of a power line in a special sealed box. In the same box, an introductory automatic machine with a fire protection device and surge arresters is installed.

The seventh way to deal with losses.

This way to reduce losses through the use of a three-phase connection. With this connection, the currents in each phase are reduced, and therefore the losses in the line can evenly distribute the load. This is one of the easiest and most effective ways. As they say: "Classics of the genre."

Conclusions.

If you want to reduce energy losses, first audit your electrical networks. If you yourself are not able to do this, now many organizations are ready to help you for your money. I hope that the tips above will help you understand where to start and what to strive for. Everything is in your power. Wish you success!