Electricity distribution: substations, necessary equipment, distribution conditions, application, accounting and control rules

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

How is the distribution of electricity and its transmission from the main power source to the consumer? This issue is quite complicated, since the source is a substation, which can be located at a considerable distance from the city, but the energy must be delivered with maximum efficiency. This issue should be considered in more detail.

General description of the process

As mentioned earlier, the initial object, from where the distribution of electricity begins, today is a power plant. Nowadays, there are three main types of station that can supply consumers with electricity. It can be a thermal power plant (TPP), a hydroelectric power plant (HPP) and a nuclear power plant (NPP). In addition to these basic types, there are also solar or wind stations, however these are used for more local purposes.

These three types of station are both the source and the first point of distribution of electricity. ForIn order to carry out such a process as the transmission of electrical energy, it is necessary to significantly increase the voltage. The farther away the consumer is, the higher the voltage should be. So, the increase can reach up to 1150 kV. Increasing the voltage is necessary in order to decrease the current strength. In this case, the resistance in the wires also drops. This effect allows you to transfer current with the least power loss. In order to increase the voltage to the desired value, each station has a step-up transformer. After passing through the section with the transformer, the electric current is transmitted to the central distribution center using power lines. PIU is a central distribution station where electricity is directly distributed.

General description of current path

Such facilities as the central distribution center are already in close proximity to cities, villages, etc. Here, not only distribution takes place, but also a voltage drop to 220 or 110 kV. After that, electricity is transmitted to substations located already within the city.

When passing through such small substations, the voltage drops again, but to 6-10 kV. After that, the transmission and distribution of electricity is carried out through transformer points located in different parts of the city. It is also worth noting here that the transmission of energy within the city to the transformer substation is no longer carried out with the help of power lines, but with the help of laid underground cables. This is much more expedient than the use of power lines. The transformer point is the last facility onin which the distribution and transmission of electricity, as well as its reduction for the last time, takes place. In such areas, the voltage is reduced to the already familiar 0.4 kV, that is, 380 V. Then it is transferred to private, multi-storey buildings, garage cooperatives, etc.

If we briefly consider the transmission path, then it is approximately as follows: an energy source (a 10 kV power plant) - a step-up transformer up to 110-1150 kV - power transmission lines - a substation with a step-down transformer - a transformer point with a voltage drop to 10- 0.4 kV - consumers (private sector, residential buildings, etc.).

Process Features

The production and distribution of electricity, as well as the process of its transmission, has an important feature - all these processes are continuous. In other words, the production of electrical energy coincides in time with the process of its consumption, which is why power stations, networks and receivers are interconnected by such a concept as common mode. This property makes it necessary to organize energy systems in order to be more efficient in the production and distribution of electricity.

Here it is very important to understand what such an energy system is. This is a set of all stations, power lines, substations and other heating networks, which are interconnected by such a property as a common mode, as well as a single process for the production of electrical energy. In addition, the transformation and distribution processes in these areas are carried out under the generalrunning this entire system.

The main working unit in such systems is the electrical installation. This equipment is designed for the production, conversion, transmission and distribution of electricity. This energy is received by electrical receivers. As for the installations themselves, depending on the operating voltage, they are divided into two classes. The first category works with voltages up to 1000 V, and the second, on the contrary, with voltages from 1000 V and above.

In addition, there are also special devices for receiving, transmitting and distributing electricity - a switchgear (RU). This is an electrical installation, which consists of such structural elements as prefabricated and connecting busbars, devices for switching and protection, automation, telemechanics, measuring instruments and auxiliary devices. These units are also divided into two categories. The first is open devices that can be operated outdoors, and closed ones, which are used only when located inside a building. As for the operation of such devices within the city, in most cases it is the second option that is used.

One of the last frontiers of the electricity transmission and distribution system is the substation. This is an object that consists of a switchgear up to 1000 V and from 1000 V, as well as power transformers and other auxiliary units.

Consideration of the power distribution scheme

To take a closer look at the process of production, transmission and distributionelectricity, you can take as an example the block diagram of the supply of electricity to the city.

In this case, the process begins with the fact that the generators at the state district power station (state regional power plant) generate voltage of 6, 10 or 20 kV. In the presence of such a voltage, it is not economical to transmit it over a distance of more than 4-6 km, since there will be large losses. In order to significantly reduce power loss, a power transformer is included in the transmission line, which is designed to increase the voltage to such values as 35, 110, 150, 220, 330, 500, 750 kV. The value is chosen depending on how far away the consumer is. This is followed by a point for lowering electrical energy, which is presented in the form of a step-down substation located within the city. The voltage is reduced to 6-10 kV. It is worth adding here that such a substation consists of two parts. The first part of the open type is designed for a voltage of 110-220 kV. The second part is closed, includes a power distribution device (RU), designed for a voltage of 6-10 kV.

Sections of the electricity supply scheme

In addition to those devices that were listed earlier, the energy supply system also includes such objects as a supply cable line - PKL, a distribution cable line - RKL, a cable line with a voltage of 0.4 kV - KL, a switchgear input type in a residential building - ASU, the main step-down substation at the plant - GPP, a power distribution cabinet or a switchboardcontrol panel device, located in the plant shop, and designed for 0.4 kV.

Also in the circuit there may be such a section as the power center - the CPU. It is important to note here that this object can be represented by two different devices. This may be a secondary voltage switchgear at a step-down substation. In addition, it will also include a device that will perform the functions of voltage regulation and its subsequent delivery to consumers. The second version is a transformer for the transmission and distribution of electricity, or a generator voltage switchgear directly at the power plant.

It is worth noting that the CPU is always connected to the RP distribution point. The line that connects these two objects does not have a distribution of electrical energy along its entire length. Such lines are usually called cable lines.

Today, such equipment as KTP - a complete transformer substation - can be used in the power grid. It consists of several transformers, a distribution or input device, designed to operate with a voltage of 6-10 kV. The kit also includes a switchgear for 0.4 kV. All these devices are interconnected by current conductors, and the kit is delivered ready-made or ready for assembly. Reception and distribution of electricity can also take place on high structures or on power transmission towers. Such structures are called either pole or mast transformer substations.(ITP).

First category electrical receivers

Today, there are three categories of electrical receivers, which differ in the degree of reliability.

The first category of electrical receivers includes those objects, in case of power failure of which there are quite serious problems. The latter include the following: a threat to human life, severe damage to the national economy, damage to expensive equipment from the main group, mass defective products, destruction of an established technological process for the production and distribution of electricity, possible disruption in the operation of important elements of public utilities. Such electrical receivers include buildings with a large crowd of people, for example, a theater, a supermarket, a department store, etc. This group also includes electrified transport (metro, trolleybus, tram).

As for the supply of electricity to these structures, they must be provided with electricity from two sources that are independent of each other. Disconnection from the network of such buildings is allowed only for the period during which the backup power source will be started. In other words, the power distribution system must provide for a quick transition from one source to another, in the event of an emergency. In this case, an independent power source is considered to be the one on which the voltage will remain even if it disappears on other sources that feed the same electrical receiver.

The first category also includes devices that must be powered from three independent sources at once. This is a special group whose work must be ensured in an uninterrupted manner. That is, it is not allowed to disconnect from the power supply even for the time the emergency source is turned on. Most often, this group includes receivers, the failure of which entails a threat to human life (explosion, fire, etc.).

Second and third category receivers

Electricity distribution systems with the connection of the second category of electrical receivers include such equipment, when the power is turned off, there will be a massive downtime of working mechanisms and industrial transport, undersupply of products, as well as disruption of the activities of a mass number of people living both within the city, as well as beyond. This group of electrical receivers includes residential buildings above the 4th floor, schools and hospitals, power plants, the power failure of which will not lead to the failure of expensive equipment, as well as other groups of electrical consumers with a total load of 400 to 10,000 kV.

Two independent stations should act as sources of energy in this category. In addition, disconnection from the main power source of these facilities is allowed until the staff on duty starts the backup source, or the duty team of workers at the nearest power supply station does this.

As for the third category of receivers, then tothey own all the remaining devices that can be powered by just 1 power supply. In addition, disconnection from the network of such receivers is allowed for the period of repair or replacement of damaged equipment for a period of not more than a day.

Principal diagram of the supply and distribution of electrical energy

Control of the distribution of electricity and its transmission from the source to the receiver of the third category within the city is most easily carried out using a radial dead-end scheme. However, such a scheme has one significant drawback, which is that if any one element of the system fails, all receivers connected to such a scheme will remain without power. This will continue until the damaged section of the chain is replaced. Due to this shortcoming, it is not recommended to use such a switching scheme.

If we talk about the connection and distribution of energy for receivers of the second and third categories, then here you can use the ring circuit diagram. With such a connection, if one of the power lines fails, you can restore the power supply to all receivers connected to such a network in manual mode, if you turn off the power from the main source and start the backup one. The ring circuit differs from the radial circuit in that it has special sections on which disconnectors or switches are in the off mode. If the main power source is damaged, they can be turned on to restore the supply, but from the backup line. It will also servea good advantage if any repairs need to be carried out on the main line. A break in the power supply of such a line is allowed for a period of about two hours. This time is enough to turn off the damaged main power source and connect the backup to the network so that it distributes electricity.

There is an even more reliable way to connect and distribute energy - this is a scheme with parallel connection of two supply lines or the introduction of an automatic connection of a backup source. With such a scheme, the damaged line will be disconnected from the general distribution system using two switches located at each end of the line. The supply of electricity in this case will be carried out in a still uninterrupted mode, but already through the second line. This scheme is relevant for receivers of the second category.

Distribution schemes for the first category of receivers

As for the distribution of energy to power the receivers of the first category, in this case it is necessary to connect from two independent power centers at the same time. In addition, such schemes often use not one distribution point, but two, and an automatic backup power system is always provided.

For electrical receivers that belong to the first category, automatic switching to backup power is installed on the input distribution devices. With such a connection system, the distribution of electric currentis carried out using two power lines, each of which is characterized by a voltage of up to 1 kV, and is also connected to independent transformers.

Other receiver distribution and power schemes

In order to most efficiently distribute electricity to second category receivers, you can use a circuit with overcurrent protection for one or two RPs, as well as a circuit with automatic backup power. However, there is a certain requirement here. These schemes can be used only if the cost of material resources for their arrangement does not increase by more than 5%, compared with the arrangement of a manual transition to a backup power source. In addition, it is necessary to equip such sections in such a way that one line can take over the load from the second, taking into account short-term overload. This is necessary, because if one of them fails, the distribution of all voltage will be transferred to the remaining one.

There is a fairly common beam connection and distribution scheme. In this case, one distribution point will be powered by two different transformers. A cable is connected to each of them, the voltage in which does not exceed 1000 V. Each of the transformers is also equipped with one contactor, which is designed to automatically switch the load from one power unit to another, if any of them the voltage will disappear.

Summing up the reliability of the network, this is one of the most important requirements that must beensure that the distribution of energy is not interrupted. To achieve maximum reliability, it is necessary not only to use the most suitable supply schemes for each category. It is also important to choose the right brands of cables, as well as their thickness and cross section, taking into account their heating and power losses during the flow of current. It is also important to follow the rules of technical operation and the technology for carrying out all electrical work.

Based on the above, we can conclude that the device for receiving and distributing electricity, as well as supplying it from the source to the final consumer or receiver, is not such a complicated process.