Generally speaking, it can be noted that the great and terrible power of electricity has long been described, calculated, listed in thick tables. Normative base, defining the paths of sinusoidal electrical signals frequency of 50 Hz is able to plunge any neophyte into horror with its volume. And despite this, any frequenter of technical forums has long known that there is no more scandalous issue than grounding. The mass of contradictory opinions in fact does little to establish the truth. Moreover, this issue is actually serious, and requires closer consideration.

Basic concepts

If we omit the introduction of the "electrician's bible" (PUE), then in order to understand the grounding technology, you need to refer (to begin with) to Chapter 1.7, which is called "Grounding and Electrical Safety Protective Measures".

In clause 1.7.2. says:

Electrical installations in relation to electrical safety measures are divided into:

electrical installations above 1 kV in networks with effectively grounded neutral (with high currents ground fault), ;
electrical installations above 1 kV in networks with isolated neutral(with low earth fault currents);
electrical installations up to 1 kV with dead-earthed neutral;
electrical installations up to 1 kV with isolated neutral.

In the vast majority of residential and office buildings in Russia, a dead-earthed neutral is used. Clause 1.7.4. reads:

A dead-earthed neutral is a transformer or generator neutral connected to a grounding device directly or through low resistance (for example, through current transformers).

The term is not entirely clear at first glance - a neutral and a grounding device are not found at every step in the popular science press. Therefore, below all incomprehensible places will be gradually explained.

When describing other options for electrical installations, it is easiest to do as in one of the Rolls-Royce instructions - "if the car breaks down, your driver probably knows what to do." At the very least, schemes other than dead-earthed neutral are slightly more common in the construction of home networks than Rolls-Royces on the streets.

Let's introduce a few terms - so it will be possible to speak at least one language. Perhaps the points will seem "taken out of context". But PUE is not fiction, and such separate use should be quite justified - as the application of individual articles of the Criminal Code. However, the original PUE is quite available both in bookstores and online - you can always turn to the original source.

1.7.6. Grounding any part of an electrical installation or other installation is called intentional electrical connection this part with a grounding device.
1.7.7. Protective grounding is the grounding of parts of an electrical installation in order to ensure electrical safety.
1.7.8. Working grounding is the grounding of any point of the current-carrying parts of the electrical installation, which is necessary to ensure the operation of the electrical installation.
1.7.9. Zeroing in electrical installations with voltages up to 1 kV is the intentional connection of parts of an electrical installation that are not normally energized with a dead-earthed neutral of a generator or transformer in networks three-phase current, with solidly grounded source output single-phase current, with a dead-earthed midpoint of the source in networks direct current.
1.7.12. A grounding conductor is a conductor (electrode) or a set of metal-connected conductors (electrodes) that are in contact with the ground.
1.7.16. A grounding conductor is a conductor connecting the grounded parts to the ground electrode.
1.7.17. A protective conductor (PE) in electrical installations is a conductor used to protect against damage to people and animals. electric shock. In electrical installations up to 1 kV, a protective conductor connected to a dead-earthed neutral of a generator or transformer is called a neutral protective conductor.
1.7.18. Zero working conductor (N) in electrical installations up to 1 kV is a conductor used to power electrical receivers, connected to a solidly grounded neutral of a generator or transformer in three-phase current networks, with a solidly grounded output of a single-phase current source, with a solidly grounded source point in three-wire DC networks. A combined zero protective and zero working conductor (PEN) in electrical installations up to 1 kV is a conductor that combines the functions of a zero protective and zero working conductor. In electrical installations up to 1 kV with a solidly grounded neutral, the zero working conductor can perform the functions of a zero protective conductor.

Rice. 4.5. difference protective earth and protective "zero"

So, a simple conclusion follows directly from the terms of the PUE. The differences between "ground" and "zero" are very small... At first glance (how many copies are broken at this point). At the very least, they must be combined (or even can be performed "in one bottle"). The only question is where and how it was done.

In passing, we note paragraph 1.7.33.

Grounding or grounding of electrical installations should be carried out:

at a voltage of 380 V and above alternating current and 440 V and above direct current - in all electrical installations (see also 1.7.44 and 1.7.48);
at rated voltages above 42 V, but below 380 V AC and above 110 V, but below 440 V DC - only in rooms with increased danger, especially dangerous and in outdoor installations.

In other words, it is not necessary to ground or neutralize a device connected to 220 volts AC. And there is nothing particularly surprising in this - there is really no third wire in ordinary Soviet sockets. We can say that the Eurostandard (or a new edition of the PUE close to it) that comes into practice in practice is better, more reliable, and safer. But according to the old PUE, we lived in our country for decades ... And what is especially important, houses were built by entire cities.

However, when it comes to grounding, it's not just about supply voltage. A good illustration of this is VSN 59-88 (Goskomarchitectura) "Electrical equipment of residential and public buildings. Design standards" Excerpt from chapter 15. Grounding (zeroing) and protective measures for safety:

15.4. For grounding (zeroing) metal cases household air conditioners, stationary and portable household appliances class I (not having double or reinforced insulation), household appliances with a power of over. 1.3 kW, cases of three-phase and single-phase electric stoves, digesters and other thermal equipment, as well as metal non-current-carrying parts technological equipment premises with wet processes, a separate conductor with a cross section equal to the phase should be used, laid from the shield or shield to which this electrical receiver is connected, and in the lines supplying medical equipment - from the ASU or main switchboard of the building. This conductor is connected to the neutral conductor of the mains. The use of a working neutral conductor for this purpose is prohibited.

This creates a normative paradox. One of the results visible at the household level was the acquisition of washing machines"Vyatka-automatic" skein of single-core aluminum wire with the requirement to perform grounding (by the hands of a certified specialist).

And one more interesting point:. 1.7.39. In electrical installations up to 1 kV with a solidly grounded neutral or a solidly grounded output of a single-phase current source, as well as with a solidly grounded midpoint in three-wire DC networks, zeroing must be performed. The use in such electrical installations of grounding the housings of electrical receivers without their grounding is not allowed.

In practice, this means - if you want to "ground" - first "zanuli". By the way, this is directly related to the famous issue of "batteries" - which, for a completely incomprehensible reason, is mistakenly considered better than zeroing(grounding).

Grounding parameters

The next aspect to consider is numerical parameters grounding. Since physically it is nothing more than a conductor (or a set of conductors), its main characteristic will be resistance.

1.7.62. The resistance of the grounding device, to which the neutrals of generators or transformers or the outputs of a single-phase current source are connected, at any time of the year should be no more than 2, 4 and 8 ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 In a single-phase current source. This resistance must be provided taking into account the use natural grounding, as well as grounding conductors for repeated grounding of the neutral wire of overhead lines up to 1 kV with a number of outgoing lines of at least two. In this case, the resistance of the ground electrode located in the immediate vicinity of the neutral of the generator or transformer or the output of a single-phase current source should be no more than: 15, 30 and 60 Ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 In a single-phase current source.

For lower voltage, more resistance is acceptable. This is quite understandable - the first purpose of grounding is to ensure human safety in the classic case of a "phase" hitting the electrical installation case. The lower the resistance, the smaller part of the potential may be "on the case" in the event of an accident. Therefore, the risk for higher voltages must be reduced first.

In addition, it must be borne in mind that grounding also serves to normal operation fuses. To do this, it is necessary that the line during the breakdown "to the body" significantly change its properties (primarily resistance), otherwise the operation will not occur. The greater the power of the electrical installation (and the voltage consumed), the lower its operating resistance, and, accordingly, the ground resistance must be lower (otherwise, in case of an accident, the fuses will not work from little change total circuit resistance).

The next normalized parameter is the cross section of the conductors.

1.7.76. Grounding and zero protective conductors in electrical installations up to 1 kV must have dimensions not less than those given in Table. 1.7.1 (see also 1.7.96 and 1.7.104) .

It is not advisable to give the entire table, an excerpt is enough:

For bare copper, the minimum cross section is 4 square meters. mm, for aluminum - 6 sq. mm. For isolated, respectively, 1.5 square meters. mm and 2.5 sq. mm. If grounding conductors go in the same cable with power wiring, their cross section can be 1 sq. mm for copper, and 2.5 sq. mm for aluminium.

Grounding in a residential building

In a normal "household" situation, power grid users (i.e. residents) deal only with the Group network (7.1.12 PUE. Group network - a network from shields and distribution points to lamps, socket outlets and other electrical receivers). Although in old houses where shields are installed directly in apartments, they have to deal with part of the Distribution Network (7.1.11 PUE. Distribution Network - a network from VU, ASU, Main Switchboard to distribution points and shields). It is desirable to understand this well, because often "zero" and "ground" differ only in the place of connection with the main communications.

From this, the first grounding rule is formulated in the PUE:

7.1.36. In all buildings, group network lines laid from group, floor and apartment shields to lamps general lighting, socket outlets and stationary electrical receivers must be three-wire (phase - L, zero working - N and zero protective - PE conductors). It is not allowed to combine zero working and zero protective conductors of various group lines. Zero working and zero protective conductors are not allowed to be connected on shields under a common terminal.

Those. 3 (three) wires must be laid from the floor, apartment or group shield, one of which is a protective zero (not earth at all). Which, however, does not prevent at all from using it for grounding a computer, a cable screen, or a "tail" of lightning protection. Everything seems to be simple, and it is not entirely clear why go into such complexity.

You can look at your home outlet ... And with a probability of about 80% you will not see a third contact there. What is the difference between zero working and zero protective conductors? In the shield, they are connected on the same bus (albeit not at one point). What will happen if we use a working zero as a protective one in this situation?

It is difficult to assume that a negligent electrician will confuse the phase and zero in the shield. Although this constantly scares users, it is impossible to make a mistake in any state (although there are unique cases). However, the "working zero" goes through numerous strobes, probably passes through several junction boxes (usually small, round, mounted in the wall near the ceiling).

It is already much easier to confuse the phase with zero there (I did it myself more than once). And as a result, 220 volts will appear on the case of an incorrectly "grounded" device. Or even simpler - a contact will burn out somewhere in the circuit - and almost the same 220 will pass to the case through the load of the electrical consumer (if this is an electric stove for 2-3 kW, then it will not seem enough).

For the function of protecting a person, frankly, this is an unsuitable situation. But for grounding connection, lightning protection of the APC type is not fatal, since a high-voltage decoupling is installed there. However, it would be unequivocally wrong to recommend such a method from a security point of view. Although it must be admitted that this rule is violated very often (and usually without any adverse consequences).

It should be noted that the lightning protection capabilities of the working and protective zero approximately equal. The resistance (up to the connecting bus) differs slightly, and this is perhaps the main factor affecting the flow of atmospheric pickups.

From the further text of the PUE, it can be seen that to zero protective conductor you need to attach literally everything that is in the house:

7.1.68. In all rooms, it is necessary to connect open conductive parts of general lighting fixtures and stationary electrical receivers ( electric stoves, boilers, domestic air conditioners, electric towels, etc.) to the neutral protective conductor.

In general, it is easier to represent the following illustration:

Rice. 4.6. Grounding scheme.

The picture is quite unusual (for everyday perception). Literally everything that is in the house must be grounded on a special bus. Therefore, the question may arise - after all, they lived without it for decades, and everyone is alive and well (and thank God)? Why change everything so seriously? The answer is simple - there are more consumers of electricity, and they are more and more powerful. Accordingly, the risk of injury increases.

But the dependence of safety and cost is a statistical value, and no one has canceled the savings. Therefore, it is not worth blindly laying a copper strip of a decent section around the perimeter of the apartment (instead of a plinth), leading everything to it, up to the metal legs of the chair, is not worth it. How not to walk in a fur coat in the summer, and constantly wear a motorcycle helmet. This is a question of adequacy.

Also, independent digging of trenches under a protective contour should be attributed to the area of ​​\u200b\u200ba non-scientific approach (in a city house, apart from problems, this will certainly bring nothing). And for those who still want to experience all the delights of life - in the first chapter of the EMP there are standards for the manufacture of this fundamental structure (in the truest sense of the word).

Summarizing the above, we can draw the following practical conclusions:

If the Group network is made with three wires, you can use protective zero. It is, in fact, designed for that.
If the group network is made with two wires, it is advisable to have a protective neutral wire from the nearest shield. The cross section of the wire must be more than the phase one (more precisely, you can consult the PUE).

With a two-wire network, it is impossible to ground the device case to a working zero. IN last resort, and being careful, you can ground the conclusions of the lightning protection with high-voltage decoupling in this way.

This could end the presentation if the network was located within the same building (or rather, one room with a single bus). In reality, home networks have large air spans (and, what is most unpleasant, they are made at a decent height). Therefore, it is necessary to separately and in detail consider the issue of lightning protection.

Most people know that a grounding system is necessary for electrical safety when installing a generator. However, they have enough general idea that grounding is a special connection of the mains or electrical appliances with a grounding mechanism at a certain point. The question arises, how to properly ground a diesel generator?

With regard to electrical safety measures, commonly used diesel power plants and their associated devices (control panel, power switching system, automatic transfer device, distributors, etc.), which includes a diesel generator set, are classified as electrical equipment with a voltage of not more than 1 kV.

These power plants are used in power networks where the neutral of a transformer or generator is connected to a grounding mechanism:

• directly
• through the resistance of devices
• doesn't connect at all

Therefore, the first version of the neutral can be called dead-earthed, and the second - isolated. The neutral of the second type is usually used in the case of using a diesel generator as an additional power source that ensures its autonomous delivery, and when reserving the main electrical network, the neutral of which is of a solidly grounded type, the generator is connected to the grounding mechanism through resistance or not connected at all. Let's name such mechanisms:

It is important to remember that the organization of the grounding of diesel power plants is a necessary measure to ensure safe use this equipment. That is why, when installing a grounding system, one should strictly follow the specially developed rules (PES-7).

This statement is true for absolutely all models that can be seen in the section diesel generators >>>

To organize grounding, grounding devices are required:

• Grounding - is a single conductor (electrode) or a system of such electrodes that are in electrical contact with the ground.
• Ground conductor- a device that connects the grounding point and the ground electrode. To connect the ground conductor to the ground electrode, you will need welding machine, and for its connection to the electric generator - a bolted connection.

The role of natural grounding can be reinforced concrete foundations buildings, pipes made of metal, etc. True, due to different reasons, when using them, the resulting resistance may not be low enough. In addition, it is forbidden to use pipelines for explosive and flammable compounds. In the event that a diesel generator is located in a building equipped with a ground loop, it is allowed to ground it through this loop. The best option for diesel station- this is the creation of an individual ground loop.

It is important to know! Taking into account the basic provisions of PES-7 for electrical networks with a dead-earthed neutral and a line voltage value of 380 V, the resistance of the grounding device should not exceed 4 ohms. It is considered optimal smallest value grounding circuit resistance indicator, which is explained by a larger value of the breakdown current to the ground and a faster response of the protective switch of the circuit.

Resistance is primarily determined by:

• the surface area of ​​the electrodes
• ground depth
• earth resistivity

In this case, the latter indicator is the main one, because it determines the resistance value to a greater extent. Soil resistivity also depends on a number of parameters: temperature, soil moisture, concentration of catholytes and electrically conductive mineral compounds. From this it follows that this indicator differs depending on the time of year and locality.

In order to qualitatively ground the electric generator and create safe conditions labor for workers, you should fulfill the entire list of requirements that apply to all components of the grounding mechanism, as well as carefully calculate its maximum allowable resistance. This calculation can be made only with a known index of soil resistivity, which is measured by special device right in the work area. In this case, you should remember about seasonal coefficients. Normally, the resulting resistance value should not exceed the calculated standard.

There is no doubt that such work should be carried out only by qualified personnel using an electrolaboratory. Over the years, our company has acquired a huge amount of knowledge in the field of installation of ground loops for power generators. The technologies for carrying out all work are fully consistent with the PUE and PTEEP. After they are carried out, we are guaranteed to issue a passport for the installed equipment.

What power to take the generator? How to install it? Where to connect it? What can be connected to an electric generator?... In this article, we have collected the 10 most popular questions and tried to answer them in a simple, understandable language. We hope that the answers to them will help you in choosing an electric generator. Here are 10 basic questions about the generator and the answers to them.

1. How powerful should I get a generator?

The expected power of the generator depends on the amount of electrical loads that you want to use at the same time. Power is measured in Watts (W). First, add up all the loads that you are going to use at the same time. Then, as a precaution, find out which household electrical appliances your home may have high inrush currents (refrigerators, air conditioners, pumps) Add it all to the total.

The fact is that some appliances, such as air conditioners, refrigerators, pumps, tend to use a lot of energy when starting (starting up) - usually 2-3 times more than they use during operation.

You need to make sure that your generator can handle relatively large appliances starting normally, make sure they don't overload the system when starting all the appliances at the same time.

The generator has two units that determine its power: nominal and maximum. The generators are provided with overload protection, which can work at the time of the simultaneous start of electrical appliances. Therefore, you should purchase a generator with some power reserve.

2. What loads should be powered by the generator?

Based on our own many years of experience installing and maintaining generators, we recommend that you provide the main consumers, which include:

1) Heating and all devices related to providing heat (boiler, pumps, etc.).

2) A couple of lighting circuits.

4) Refrigerator.

5) Microwave.

6) Garage doors.

7) Downhole pump.

8) Alarm.

If the power of the backup generator is sufficient, then secondary loads can also be connected: drainage pump, ventilation...

Equipment manufacturers indicate the power of the devices on the devices themselves or in the product passport. Also on many sites you can find an online calculator that will help you choose the power of the generator.

4. Do I need to hire an electrician to connect the generator to the electrical network at home?

Most safe way connecting the generator to the electrical network at home is to use additional device- AVR - automatic switching on of the reserve. The ATS is connected to the mains after the meter, and the generator is connected directly to the automation. When you start the generator, it disconnects the house from the city power grid and powers only those electrical appliances that you have allocated. Thus, the generator will not be overloaded.

If you are an amateur electrician, you have some knowledge of electricity but no experience in installing equipment of this type, it is best to contact a specialist to install the equipment. After all, the reliability of the entire power system of your home largely depends on how competently and efficiently the installation and commissioning of equipment is carried out.

5. Can't I just plug the generator into an outlet?

No and no again! We have already seen many times what this can lead to. This is very dangerous for a number of reasons. For example, if someone forgets to disable the main circuit breaker, then the generator can send power supply to the external network with all the ensuing consequences, if at that time repair work is underway on the line ...

Key points to know for correct connection generators are discussed in this article:

6. What is the difference between standby generator and emergency generator?

The backup generator is installed permanently and is designed to supply most electrical appliances. The emergency generator is a small, portable unit that can be taken outside the premises and connected to the ATS. Or it can be connected to electrical loads via extension cords.

7. If it's raining or snowing outside, can I put the generator in the garage and run it there as long as the door is left open?

No. Never run a generator inside a home, inside a garage, under a shed, on a porch, inside a porch, or near open window. Even with the garage open, carbon monoxide (CO) from generator exhaust can cause poisoning or, in the worst case, death.

8. What other safety tips should I keep in mind?

If the generator is installed permanently, use smoke detectors and carbon monoxide detectors, at least when using the generator. The generator should be located at least three meters from the house to minimize the risks of poisoning carbon monoxide(CO). Never fill the generator with fuel while it is hot.

9. Generators are loud enough. What can be done about it?

Unfortunately there aren't many options. Use generators inverter type, where the speed depends on the load. You can also purchase generators in a soundproof casing. In addition, you can purchase a special soundproof all-weather container in which the generator is placed.

Some craftsmen are experimenting with additional mufflers from motorcycles and ATVs. This can be done if you have the necessary skills. But be aware that in most cases this will void the generator warranty.

The easiest way to reduce noise from a mini power plant is to reduce the electrical load.

10. Do I need to ground the generator?

Follow the instructions in the user manual. If the manual requires the generator to be grounded, do so. The easiest way is to connect a 4-6 mm wire to the ground terminal on the generator. Connect the wire to a copper or iron 1.5 m rod that can be driven into the soil next to the generator.

As an alternative to the ground rod, you can connect the ground wire from the generator to inside the house at the main switchboard.

The activities were carried out in accordance with the EMP 7th ed. Chapter 1.7.

Let us consider the case when the object of the protective grounding installation is the DGU container (diesel generator set). In accordance with the customer's data, the soil at the proposed installation site of the EGE-4 grounding device (alluvial sandy loam gray color soft-plastic) and EGE-3 (alluvial-deluvial loam Brown hard plate), ground water at a depth of 2.5m.

Let us take the specific soil resistance equal to 100 Ohm∙m.

In accordance with the PUE, clause 1.7.101, the resistance of the grounding device to which the neutrals of the generator or transformer or the outputs of a single-phase current source are connected, at any time of the year should be no more than 4 ohms, respectively, at line voltages of 380 V of a three-phase current source or 220 V of a single-phase current source current.

The DGU container belongs to the ordinary ones in terms of lightning protection in accordance with the Standards and to the 3rd category in accordance with the RD.

Protection of buildings from lightning discharges is carried out with the help of lightning rods. A lightning rod is a device that rises above the protected object, through which the lightning current, bypassing the protected object, is diverted to the ground. It consists of a lightning rod that directly perceives a lightning discharge, a down conductor and a ground electrode.

A set of measures to ensure the necessary requirements for a lightning protection system is represented by the following solutions:

Installation of one lightning rod-mast for 3 concrete bases 4 meters high. Installation is carried out on the roof of the container;

The device of two down conductors with the use of copper-plated wire D=8 mm. Down conductors should be located no closer than 3 m from the entrances or in places inaccessible to people. Mounting of down conductors on the roof is carried out using clips GL-11706. The down conductor is fixed to the vertical surfaces of the building using clamps GL-11704A.

Installation of a grounding device, consisting of five vertical electrodes (copper-plated pins with a diameter of 14 mm.) 4.5 m long, united by a horizontal electrode (copper-plated strip 30 × 4 mm). The distance between the vertical electrodes is at least 5 meters, the distance from the horizontal electrode to the walls of the container is 1 m, the depth is 0.5 meters.

The connection of the down conductor with the output of the copper-plated strip from the ground is carried out using the control clamp GL-11562A.

Calculation of the resistance of the grounding device:

Horizontal electrode resistance:

where p - resistivity soil, Ohm m;

b - strip width of the horizontal electrode, m;

h is the depth of the horizontal grid, m;

L mountains - the length of the horizontal electrode, m.

Vertical electrode resistance:

Where ρ eq - equivalent soil resistivity, Ohm m;

L- length of the vertical electrode, m;

d- diameter of the vertical electrode, m;

T- deepening - the distance from the earth's surface to the ground electrode, m;

Where t- deepening of the top of the electrode, m

Grounding device impedance:

Where n- number of sets;

k isp - utilization factor;

The design resistance of the grounding device is 3.89 ohms.

Figure 1 - Protection zone B according to AD

Figure 2 - Layout of grounding and lightning protection elements

Scroll necessary materials is shown in table 1.

Table 1 - List of material requirements

No. p / p	Image	Code	Name	Quantity
1.		GL-21121	GALMAR Lightning rod-mast (4.0 m; on 3 concrete bases; single-stage cable support; galvanized steel)	1 PC.
2.		GL-11149-50	GALMAR Copper-plated steel wire (D8 mm; coil 50 meters)	10 pieces.
3.		GL-11706	GALMAR Flat roof holder for down conductor (D8 mm; for gluing; plastic)	4 things.
4.		GL-11707	GALMAR Decorative protective cover for holder GL-11706	4 things.
5.		GL-11704A	GALMAR Facade clamp for down conductor (painted galvanized steel)	6 pcs.
6.		GL-11562A	GALMAR Control clamp for connecting down conductors wire + strip (painted galvanized steel)	2 pcs.
7.		GL-11075-50	GALMAR Copper-plated strip (30*4 mm / S 120 mm²; coil 50 meters)	1 PC.
8.		GL-11075-10	GALMAR Copper-plated strip (30*4 mm / S 120 mm²; coil 10 meters)	1 PC.
9.		ZZ-005-064

6. Neutral mode.

Operating modes of neutrals in electrical installations

Neutrals of electrical installations are called common points three-phase windings generators or transformers connected in a star.

Depending on the neutral mode, electrical networks are divided into four groups:

1) networks with ungrounded (isolated) neutrals;
2) networks with resonantly grounded (compensated) neutrals;
3) networks with effectively grounded neutrals;
4) networks with dead-earthed neutrals.

According to the requirements of the Electrical Installation Rules (PUE, Ch. 1.2).

Networks with rated voltage up to 1 kV, powered by step-down transformers connected to networks with Un > 1 kV, are made with dead neutral grounding.
Networks with Unom up to 1 kV, powered by an independent source or an isolation transformer (in terms of ensuring maximum electrical safety in case of earth faults), are made with an ungrounded neutral.
Networks with Unom = 110 kV and above are made with effective neutral grounding (the neutral is grounded directly or through a small resistance).
Networks 3 - 35 kV, made with cables, at any earth fault currents, are made with neutral grounding through a resistor.
Networks 3-35 kV with air lines, with a closing current of not more than 30 A, they are performed with neutral grounding through a resistor.

Compensation of the capacitive current to earth is required at values ​​of this current under normal conditions:

In networks of 3 - 20 kV with reinforced concrete and metal supports of overhead lines and in all networks of 35 kV - more than 10 A;

In networks that do not have reinforced concrete or metal supports VL:
at a voltage of 3 - 6 kV - more than 30 A;
at 10 kV - more than 20 A;
at 15 - 20 kV - more than 15 A;

In circuits of 6 - 20 kV blocks, the generator - transformer - more than 5A.

Electrical installations voltage above 1 kV according to the Electrical Installation Rules (PUE) are divided into installations with high earth fault currents (single-phase earth fault current exceeds 500 A) and installations with low earth fault currents (single-phase earth fault current is less than or equal to 500 A).

In installations with high earth fault currents neutral connected to grounding devices directly or through low resistances. Such installations are called installations with dead-earthed neutral.

In installations with low earth fault currents, neutrals are connected to earthing devices through elements with high resistances. Such installations are called installations with isolated neutral.

In installations with dead-earthed neutral any earth fault is a short circuit and is accompanied by a large current.
In isolated neutral installations, shorting one of the phases to ground is not a short circuit (short circuit).

The passage of current through the place of the circuit is due to the conductivities (mainly capacitive) of the phases relative to the ground.
The choice of the neutral mode in installations with voltages above 1 kV is made taking into account the following factors: economic, the possibility of switching from a single-phase fault to a phase-to-phase fault, the impact on the breaking capacity of circuit breakers, the possibility of damage to equipment by ground fault current, relay protection, etc.

IN electrical networks RAO UES of Russia has adopted the following neutral operating modes:

• electrical networks with rated voltages of 6 ... 35 kV operate with low currents
• earth faults;
• at low capacitive earth fault currents - with isolated neutrals;
• at certain excess values capacitive currents- with neutral grounded
• through the arc reactor.

If in one of the phases three-phase system working with isolated neutral, a short circuit to the ground has occurred, then its voltage with respect to the ground will become equal to zero, and the voltage of the remaining phases with respect to the ground will become equal to linear, i.e., it will increase by 3 times. The earth fault current will be small because, due to the isolation of the neutral, there is no closed circuit for it to pass. The earth fault current in an isolated neutral system will be small and will not cause a line trip. Thus, the isolation of the neutral of the power supply ensures the reliability of the power supply, since it does not affect the operation of consumers.

However, in networks with large capacitive currents to the ground (especially in cable networks), an intermittent arc occurs at the point of the circuit, which periodically goes out and re-ignites, which induces in a circuit with active, inductive and capacitive elements emf exceeding the rated voltage by 2.5 ... 3 times. Such stresses in the system at single-phase short circuit on the ground are not allowed. To prevent the occurrence of intermittent arcs between neutral and earth, an inductive coil with adjustable resistance is included.

Increasing the voltage with respect to earth in the non-faulted phases in the presence of weak points in the insulation of these phases can cause phase-to-phase short circuit,. In addition, the voltage in undamaged phases increases by a factor of 3, therefore, it is required to isolate all phases on line voltage, which leads to an increase in the cost of machines and apparatus. Therefore, although it is allowed to operate the network with an isolated neutral during a phase-to-earth fault, it must be immediately detected and eliminated.
Electric networks with a rated voltage of 110 kV and above operate with high earth fault currents (with effectively earthed neutrals).

For offline mobile units neutral is selected isolated.

According to the "Electrical Installation Rules" when supplying stationary electrical receivers from autonomous power sources, the neutral mode of the power source and protective measures must correspond to the neutral mode and protective measures taken in the networks of stationary electrical receivers. Therefore, for diesel generators used as a "backup industrial network”, the neutral is selected dead-earthed.