Excursion to the substation 220/110/20

    Before electricity from a power plant reaches our outlet, its voltage is first increased to hundreds of thousands of volts, and then lowered back to 220V. They make such transformations at transformer substations.

    The most important characteristic of a substation is voltage levels on the upper and lower sides. What is written in the title just means that there are 220 thousand volts on the upper side and two voltage levels of 110 and 20 kV on the lower side. That is, in fact, these are two substations in the same territory. And in our outlet according to the classification of power engineers of 0.4 kV, that's why. that between the phases is 400 volts (before it was 380 but the standards have changed a long time ago).

    The substation begins with an open switchgearwith a safety briefing, then go to the upper side of the substation in an open switchgear - outdoor switchgear.


    In general terms, power lines, disconnectors, gas-insulated switches, and portals with bus sections are visible.
    Portals are metal structures above the entire visible economy, and the bus section is the part of the substation circuit that can be disconnected from the rest of the circuit by switches and disconnectors. This substation can be powered from either end of the power line, and can also disconnect the line. I don’t know about this particular power line, but unlike the power cord of your PC, in which the current always comes from the outlet, high voltage power lines are for the most part included in a single power system and energy from such lines can flow from different sources (located from different sides of the line) to different consumers at different times. To do this, all generators included in a single network operate strictly synchronously.
    Switching of the 220 kV line is carried out by gas-insulated switches.


    SF6 gas or sulfur hexafluoride is pumped into the circuit breakers for better arc extinction when the contacts are disconnected. Everyone noticed a spark in the house switch or in the socket when the plug was turned off - this is the same principle, but many orders of magnitude more. There are vacuum, oil circuit breakers, but SF6 are considered the most reliable today for this voltage level.

    In the photo I showed a pressure gauge, it can be seen from the ground so that an employee can diagnose a gas leak. This leakage gas circuit breaker model must not be turned off under load - it will collapse.

    Also, disconnectors are necessarily present at Russian substations:


    This is essentially also a switch, but completely open, you can disconnect the disconnector only without load. It is needed to create a “Visible Physical Gap” - this is a prerequisite for the safe execution of work at substation facilities. That is, it is not enough to turn off the SF6 circuit breaker and ground it, it is necessary that a physical break is visible.

    Switches and disconnectors can be controlled both from the substation control panel and manually using special handles.

    One of the interesting devices for an electronic engineer: a high-frequency trap



    In fact, the coil and capacitor make up the LC - filter, which does not pass a high-frequency signal into the network. A high-frequency signal comes from another substation or power station, its frequency is in the region of 40 kHz, and is used to transmit information, mainly a protection and automation system. The transmission speed is very low, but the reliability of the method has proven itself for decades and this type of communication is required when constructing such objects. The signal power is of the order of 1 kV and it is very difficult to technically distort or damp it.
    It is impossible to measure directly currents and voltages in such networks with devices, therefore transformers are used for the operation of automation and measurements. We saw a current transformer in the picture with a gas-insulated switch, and voltage transformers look like this:


    After conversion, we get a maximum of 100 volts or 5 amperes - all shield measuring instruments and relay protection and automation devices (relay protection and automation) are configured for these values. Unlike the standard industrial controllers: 1-10V and 4-20mA, the levels of 100V and 5A are much more resistant to interference.

    Another device on the upper side is surge protection:


    When a lightning strike, the varistor resistance drops sharply and dumps excess energy into the ground. And yes it works on 190kV, because in a 220kV power transmission line each phase relative to the earth has a potential of less than 190kV.

    And here is the heart of the substation - an autotransformer 250MVA (megavolt ampere):


    The transformer has many devices to ensure its operation and protection. In case of fire, it is extinguished with water, although oil is not extinguished with water, but if there is no money for foaming, and you really want it, then you can do it with water. A spray system is used during the operation of which a cloud of steam and water forms around the transformer, which blocks the access of oxygen and the fire stops.

    It is called an autotransformer because it has a connection between the primary and secondary windings as in LATR - and it is believed that its efficiency is higher than that of a classical transformer.
    This transformer has two secondary windings 110 and 10. A 10 kV winding is used only for self-supply. As practice has shown, if the 10Kw winding is loaded at nominal value, then not provided electromagnetic fields and bolts are formed, with which the transformer bottom is screwed on and begin to glow.

    The load in the network is not constant and this transformer also provides voltage regulation for the load. The


    handle can be turned only during repair and adjustment, during working hours - only the electric drive and automation.

    On the whole high side (by the way, they call it high by the voltage level, everything is physically in the same plane) the cracks of discharges are constantly heard and this quickly tires.
    After the autotransformer, the low side begins with a voltage level of 110
    Everything is the same here: open switchgear, switches, portals, bus sections ...

    Voltage transformers:


    Disconnectors and switches:


    And the electricity goes to other substations

    But there is also a second low side, it starts after the 110/20

    transformer, the smaller transformer, the cooling system is passive, it's already a classic transformer, not an autotransformer. But all systems of drainage of oil and air, protection are also present. There is silence on the 110 side, no cod discharges at all.

    The lowest side of the substation is 20kV. represented by indoor switchgear - closed switchgear

    If on an outdoor switchgear 220 kV it is forbidden to get closer to live parts closer than 4 meters, in a 20 kV indoor switchgear you can safely touch the equipment

    Everything is closed, marked, controlled by remote control or manually, it is impossible to open a cell just like that - everything is blocked by automation.

    For repair, cells are rolled out on such carts:

    For control and management, domestic controllers are used:

    Next, a voltage of 20 kV is supplied to local substations via underground cables. Networks with voltage higher than 0.4 kV are isolated from the ground (well, not quite 100%, but there is no usual zero in such networks). In the event of a breakdown to the ground, the current nevertheless flows, but is perceived as normal consumption, and the arc at the same time spoils the cable insulation and ultimately leads to its damage and interphase short circuit. To prevent this, they came up with a special system:
    A transformer with a midpoint is placed on three phases of the cable, and with an equal load on the phases, the voltage at the midpoint relative to the earth is zero, and when the earth is shorted, the voltage increases and is an indicator of the problem. To identify a specific cable. in which a short circuit has occurred use large resistors.

    There are also arc suppression coils that allow you to compensate for the potential difference, extinguish the arc, and according to the stories, sometimes the insulation is delayed and cable repair is not required.

    Substation main console:

    on the cabinets a diagram of the substation is drawn and the controls are inscribed in the circuit - before the entrance, strictly reminded that no knobs are turned or pressed. Behind the console there are a lot of cabinets with AC and DC power systems (all protection works on a fully autonomous DC network), alarm systems, fire extinguishing systems, etc. All are closed.
    This is what a high-frequency communication device looks like, the very thing that is connected to a high-frequency trap and communicates with its own kind in other substations.

    In conclusion, we were allowed into the telemetry room and RPA: I was expecting something interesting, but the room was filled with closed cabinets with incomprehensible abbreviations. There was no time left and it was not possible to ask for details.

    Here is one of the closets where something is visible:

    In the photo there are universal level converters that convert 100V 5A to 24V 20mA.
    Part of relay protection assemblies is assembled on mechanical relays, part on logic controllers. All information is displayed on the dispatcher’s workstation on the PC screen, from where it can be controlled. Also, all the information goes to the central control center of the network organization.

    On this our tour ended, handed over the helmets and once again looking from the side of the outdoor switchgear, escorted by the guards left the territory.

    From the point of view of me as an IT professional, the approaches to protection, blocking, management, control are organized at the highest, one can say “iron” level - it is quite possible to borrow when building information systems.

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