What is an electrical substation? Electrical substations and switchgears

Specialists in electrical engineering know what electrical stations and substations are, what they are designed for and how they are arranged. They know how to calculate their power and all the necessary parameters, such as the number of turns, the cross-section of the wire and the dimensions of the magnetic circuit. This is taught to students in technical universities and technical schools. People with a liberal education know that buildings that often stand alone in the form of houses without windows (they are liked by graffiti lovers) are needed to power homes and businesses, and they should not be penetrated, elusive emblems in the form of skulls and lightnings speak about it eloquently , Attached to dangerous objects. Perhaps, many do not need to know more, but information is not superfluous.

A little physics

Electric power is a commodity for which it is necessary to pay, and it is very insulting if it is spent in vain. And this, as with any production, is inevitable, the task is only to reduce in vain losses. The energy is equal to the power multiplied by the time, therefore in the further reasoning it is possible to operate with this concept, since time flows constantly, and it is impossible to turn it back, as it is sung in a song. Electric power, in rough approximation, without taking into account reactive loads, is equal to the product of the voltage per current. If we consider it in more detail, the cosine fi, which determines the ratio of the consumed energy with its useful component, called the active component, falls into the formula. But this important indicator has no direct relation to the question of why a substation is needed. Electric power, therefore, depends on the two main participants of the laws of Ohm and Joule-Lenz, voltage and current. Low current and high voltage can form the same power as vice versa, high current and low voltage. It would seem, what's the difference? And it is, and very large.

Warm up the air? Thank you!

So, if you use the formula of active power, you get the following:

• P = U x I, where:
  
  U is the voltage measured in Volts;
  I is the current measured in Amperes;
  P - power, measured in Watts or Volt-amperes.

But there is one more formula that describes the already mentioned Joule-Lenz law, according to which the thermal power released when the current passes is equal to the square of its magnitude multiplied by the resistance of the conductor. To heat the air that surrounds the power line means waste energy. And it is possible to reduce these losses theoretically in two ways. The first of these involves a reduction in resistance, that is, a thickening of the wires. The larger the cross-section, the lower the resistance, and vice versa. But I do not want to spend metal in vain, it's expensive, copper all the same. In addition, double consumption of conductor material will not only lead to an increase in cost, but also to weighting, which in turn will lead to an increase in the laboriousness of mounting high-rise lines. And the supports will need more powerful ones. And the losses will be reduced only by half.

Decision

To reduce the heating of wires during the transfer of energy, it is necessary to reduce the amount of the passing current. This is quite clear, because its reduction by half will lead to a reduction in losses fourfold. And if ten times? The dependence is quadratic, so the losses will be a hundred times less! But the power must "swing" the same, which is needed by the aggregate of consumers waiting for it at the other end of the power line, going from the power plant sometimes for hundreds of kilometers. The conclusion is that it is necessary to increase the voltage by the same amount as the current is reduced. The transformer substation at the beginning of the transmission line is just for this purpose intended. From it, wires come out under very high voltage, measured in tens of kilovolts. Throughout the distance separating the TPP, HPP or nuclear power plant from the locality where it is addressed, energy travels with a small (relatively) current. The consumer needs to obtain power with the given standard parameters, which in our country correspond to 220 volts (or 380 V inter-phase). Now we need not increasing, as at the power line entrance, but a stepping down substation. Electric energy is supplied to the switchgears in order to light the houses in the houses, and the rotors of the machine tools were turned in the factories.

What's in the box?

From the foregoing it is clear that the most important part in the substation is a transformer, usually three-phase. There can be several. For example, a three-phase transformer can be replaced by three single -phase transformers . More quantity can be due to high power consumption. The design of this device is different, but in any case it has impressive dimensions. The more power is given to the consumer, the more serious the structure looks. The installation of an electrical substation, however, is more complicated, and includes not only a transformer. Here, too, is equipment intended for switching and protecting an expensive unit, and also most often for cooling it. Another electrical part of the stations and substations contains switchboards equipped with control and measuring equipment.

Transformer

The main task of this facility is to bring energy to the consumer. Before sending, the voltage should be increased, and after it is received, lower it to the standard level.

Despite the fact that the scheme of the electrical substation includes many elements, the main one of them is still a transformer. There is no fundamental difference between the device of this product in a conventional power supply unit of a household appliance and industrial high-power samples. The transformer consists of windings (primary and secondary) and a magnetic core made of a ferromagnet, that is, a material (metal) reinforcing the magnetic field. The calculation of this device is quite a standard educational task for a student at a technical college. The main difference between the substation transformer and its less powerful counterparts, striking in addition to its dimensions, is the presence of a cooling system, which is a combination of oil pipelines encircling the heating coils. The design of electrical substations, however, is not an easy task, since many factors must be taken into account, from climatic conditions to the nature of the load.

Traction power

Not only houses and businesses consume electricity. Here everything is clear, you need to apply 220 volts AC against a neutral bus or 380 V between phases with a frequency of 50 hertz. But there is also a city electric transport. Trams and trolley buses require voltage not variable, but constant. And different. On the trolley wire, there should be 750 volts (relative to the ground, ie rails), and the trolleybus is required on one conductor of zero and 600 volts of direct current on the other, rubber wheel protectors are insulators. So, we need a separate very powerful substation. The electrical energy on it is transformed, that is, it is straightened. Its power is very high, the current in the circuit is measured in thousands of amperes. Such a device is called a draft device.

Substation protection

Both a transformer and a powerful rectifier device (in the case of traction power supplies) are expensive. If an emergency situation arises, namely a short circuit, a current appears in the secondary circuit (and therefore the primary one). Hence, the cross-section of conductors is not calculated. The electrical transformer substation will begin to heat up due to resistive heat dissipation. If you do not provide for such a scenario, then as a result of a short circuit in any of the peripheral lines, the winding wire will melt or burn. To avoid this, different methods are used. This is differential, gas and maximum current protection.

Differential compares the values of the current in the circuit and the secondary winding. Gas protection is triggered by the appearance in the air of combustion products insulation, oil and so on. Current protection disconnects the transformer when the current exceeds the maximum set value.

The transformer substation should automatically switch off also in the event of a lightning strike.

Types of substations

They are different in power, in purpose and device. Those of them that serve only to increase or decrease the voltage, are called transformer ones. If it is also necessary to change other parameters (rectification or frequency stabilization), the substation is called transforming.

In terms of its architectural design, the substations are built-in, built-in (adjacent to the main facility), intra-workshop (located inside the production premises) or a stand-alone auxiliary building. In some cases, when high power is not required (when organizing the power supply of small settlements), the mast construction of the substations is applied. Sometimes for the placement of the transformer, the transmission line supports are used , on which all the necessary equipment is mounted (fuses, arresters, disconnectors, etc.).

Electrical networks and substations are classified by voltage (up to 1000 kV or more, that is high voltage) and power (for example, from 150 VA to 16 thousand kVA).

According to the schematic feature of outdoor connection, the substations are nodal, dead-end, through-pass and tap-off.

Inside the camera

The space inside the substation in which the transformers, buses and equipment providing the operation of the entire device are located is called a camera. It can be fenced or closed. The difference between ways to alienate it from the surrounding space is small. The enclosed chamber is a completely isolated room, and the enclosed chamber is behind incomplete (mesh or lattice) walls. They are produced, as a rule, by industrial enterprises for standard projects. Maintenance of power supply systems is carried out by trained personnel having the admission and necessary qualification, confirmed by the official document on the permission to work on high-voltage lines. Operational supervision of the substation is performed by an on-duty electrician or power engineer, located near the main switchboard, which can be located remotely from the substation.

Distribution

There is another important function performed by the power substation. Electric energy is distributed among consumers according to their norms, and in addition, the load of the three phases should be as uniform as possible. In order for this task to be successfully solved, there are switchgears. RUs operate at the same voltage and contain devices that perform switching and protection of the lines from overload. With the transformer RU are connected by fuses and breakers (single-pole, one for each phase). Distribution devices in the place of placement are divided into open (located in the open air) and closed (located inside the premises).

Security

All work done in an electrical substation is classified as particularly risky, and therefore requires emergency measures to ensure work safety. In general, repairs and maintenance are carried out with full or partial de-energizing. After the voltage is disconnected (the electricians say "removed"), provided all the necessary tolerances are present, busbars are grounded to avoid accidental switching. For this, the warning signs "People work" and "Do not include!" Are also intended. The personnel serving high-voltage substations are systematically trained, and the skills and knowledge acquired are periodically monitored. Tolerance No. 4 gives the right to perform work on electrical installations over 1 kV.