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

Consider the case when the installation object protective earth is a 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 source leads are connected single-phase current, at any time of the year should be no more than 4 ohms, respectively, at line voltages of 380 V source three-phase current or 220 V single-phase current source.

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 ρ is the resistivity of the 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

Bought a 1 phase generator. The neutral is separated from the ground. The house has a 3-phase input. On the input panel in the house, zero and earth are on the same block, that is, they are connected.
I plan to connect the generator through a reversible 4-pole switch, i.e. phases and zero in the gap. What about generator grounding? Is it possible to throw houses on the ground?

It is not possible, but by default, the generator frame must be connected to the house charger with a power cable. In general, worse, budgetary options allowed by the norms and common sense are possible and more. best options when the generator frame is not connected to the house charger. In any case, the generator frame must be grounded.

In addition to the fact that in 1-phase generators there is no zero by default, any power output should be groundedit is forbidden!

GOST R 50783-95 said:

ELECTRIC UNITS AND MOBILE POWER PLANTS WITH INTERNAL COMBUSTION ENGINES
10 SAFETY REQUIREMENTS

10.3 Schematic electrical connections mobile electrical units and three-phase alternating current power plants must have an isolated neutral.It is not allowed to use any devices that create an electrical connection of phase and (or) zero wires or neutral with housing or neutral conductors or neutral with housing or earth directly or through an artificial zero point, except for devices for suppressing radio interference.

10.4 In mobile electrical units and power plants with a capacity of 1 kW and above rated voltage from 115 V and abovethere must be a device for permanent insulation monitoring, which allows you to measure (estimate) the insulation resistance relative to the body (ground) of the conductive parts of the electrical unit and power plant that are energized. For operation in conjunction with the local electrical network, mobile generating sets and power plants must have an automatic shutdown device. These devices should be monitored for proper operation.

It is not allowed to use permanent insulation monitoring devices operating on the principle of voltage asymmetry.

Unfortunately, only some manufacturers of autonomous power supply sources indicate this.

ENERGO generator instruction said:

This manual is valid for petrol generating sets of the company:
SAWAFUJI ELECTRIC COMPANY (Japan)

EA 6500 (SH 6500 EX)

HAZARD WARNINGS
Do not connect to the local power supply without a disconnector installed by a qualified electrician. …

BASIC ELECTRICAL SAFETY RULES
― to prevent the operation of the electric unit in case of a short circuit to the case ...

When operating the unit IT IS FORBIDDEN:
ground the neutral or connect it to the body;

Illiterate in electrical safety, the owners of autonomous power supply sources, who themselves do not comply with and advise others not to comply with these standards, argue that they are right by stating that portable and smoke-type generators and other autonomous power supplies of 220/380 volts do not apply when they are supplied from home, as they constantly stand in one place.

It’s necessary to think of such a statement, like the fact that the generator is called portable, then they wear it during operation, or because the generator constantly stands in one place, the electricity generated by it becomes safe!

Also, sellers-installers who are illiterate in electrical safety, including some certified service centers connecting generators, or just hacks, tightly connect one of the generator outputs with neutral wire supply network, since without switching the neutral wire, the circuit, installation, cheaper and easier to find components, as well as for fooling the clumsy flame control circuit of some boilers, arguing that they say they do it right because they did it many times and how it works, which is comparable to an illiterate statement that it’s enough to do wiring without VDT, grounding, since millions of houses do not have VDT, 2 wires and millions have not been killed, so install differential protection and use wiring with PE not needed.

Even if an autonomous power source is foolishly connected to a power supply system with a TN grounding type, then it is impossible to somehow connect one of the power outputs of an autonomous power source to the neutral wire of the mains!

GOST R 50571-4-44-2011 (IEC 60364-4-44:2007) said:

SAFETY REQUIREMENTS. PROTECTION AGAINST VOLTAGE DEVIATIONS AND ELECTROMAGNETIC INTERFERENCE.

444.4.7 Switching power supplies
In TN systems, switching power from one source to another sourcemust be carried out using a switching device that simultaneously switches the line conductors and the neutral conductor, if present in the electrical installation (see figures 44. R9A, 44. R9B, 44. R9C).

Non-compliance with the above-mentioned electrical safety standards is every day an increasing danger for those who violate these standards, animals, as well as for installers repairing the supply network, since every day there is more autonomous power supply sources and their power for the population illiterate in electrical safety!

This is not to mention that non-observance of the above-mentioned standards increases the likelihood of generator failure, up to the impossibility of repair, for example, due to a minor leak in the generator insulation, even if the generator is not working, since the machine does not protect against such a malfunction, and with such a dangerous connection, it will not work to use VDT!

It should also be borne in mind if a circuit is being made that during a power failure in the network, only part of the wiring at home is powered from an autonomous source of electricity 220/380 volts, and the rest of the wiring remains connected to the mains, which is better not to do, then the installation of lines in the shield and in the wiring powered by an independent source of electricity and connected to the mains, which are located together, must be designed for 660 volts! This also applies to lines located nearby, fed from different autonomous power supplies 220/380 volts!

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 grounding 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.

Cast natural grounding may speak 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 indicator resistivity soil, 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.

When connecting an electric generator, you have to deal with three networks: a common centralized network, a network of energy consumers and wiring from the generator. Their connection and interaction determines the specific connection scheme. There are three ways to power devices that consume energy from an electric generator.

Energy consumers are connected directly to the generator socket. This circuit is very simple and needs no explanation. It does not require the creation of any additional circuits and network connections.

The generator is connected to a consumer network that is not connected in any way with a centralized network (it may not exist at all). In this case, the wires coming from the generator are permanently connected to the wiring of energy consumers. This connection scheme of the gas generator (diesel generator) is called constant. The main thing to take care of in this case is that the cross sections of the wiring wires correspond to the rated current of the generator.

The generator, through manual or automatic switching devices, is connected into a single circuit with a centralized network and consumer wiring. This connection scheme of the gas generator allows, in the event of a power failure in the centralized network, to easily and quickly power all consumers from the generator. It's called a backup.

Unlike the first method, which does not require any preparation (the plug of the powered tool or device is connected directly, or through an extension cord, to the socket located on the generator control panel), the last two methods require competent preparatory work. The third (reserve) connection scheme is the most complex and in demand.

Generator connection diagram as a backup power source

Scheme with manual mode switching. In the event of a power failure in the central network, by turning the key of the switch or the handle of the knife switch, they break the consumer network with the central network and connect it to the wires from the generator. The switch must guarantee the impossibility of simultaneous connection of electrical consumers to the centralized power grid and the generator (there must be an intermediate neutral position).

Reversing switches or toggle switches are used as a manual switch. When choosing these devices, you should pay attention to their rated currents. They must correspond to the consumed current (not be lower). Their design and connection diagram can differ significantly, for example, the diagram below shows a three-pole switch (one pole is not used) OT40F3С (far from the cheapest option).

In addition to the manual switch, you can put an indicator, the function of which is to indicate the presence or absence of voltage in the central network. It turns on between the phase and zero of the central network. These can be special modular 220V indicators, or cheaper (20 times) 220V indicator lights. closed case and already soldered wires.

The weak point of these indicators is that they are connected before the fuses.

Scheme with automatic mode switching. Automatic scheme connection of an electric generator allows, in the event of a power failure in the central network, to turn on the generator automatically without human intervention. This work is performed by the AVR (automatic transfer switch), consisting of a whole set of devices - contactors, voltage control relays, circuit breakers, indication elements.

The generator, which is switched on automatically, must have an electric starter. To turn on backup source to work, you must disable centralized network, start and warm up the generator, connect the wiring from it to the consumer network. When a central tension appears, reverse work. All this is performed by the AVR block.

Exist various systems automatic input of a reserve, differing in their functionality. They work as follows, using the example of the Champion ATS block for gasoline generator GG7000E. When the power supply from the central network is interrupted, the program for starting the ATS unit is launched. First, energy consumers are disconnected from the centralized network. After 2-3 seconds, the generator engine starts and its operation is checked. During normal operation of the unit, after 12 seconds. after starting the engine (warming up), the generator is connected to consumers of electricity.

When power is restored from common network, the system monitors the stability of the supplied electricity. If stability is detected for 10 seconds, ATS automatically switches consumers to power from the public network. The generator runs without load for another 5 seconds, then the ATS system stops it.

Load switching order

Connection errors

Both of these are unacceptable. Plugging the generator wires into a consumer network socket, in case of a heavy load, can cause destruction of the socket and electrical wiring with a risk of fire, since the size of the socket contacts and the cross section of its wires are not designed for high currents flowing in the generator network. And if you do not turn off the centralized network (for example, forgetting), then when voltage appears in it, the generator will fail.

Installation of an electric generator

The installation site of the gas generator or diesel generator must be dry and level. There must be no flammable objects nearby.

Not every the room is suitable to install a power generator. There are certain ventilation requirements. So, in a closed room, it is necessary to organize supply and exhaust ventilation using a duct system or built-in fans. Thus, the supply of cold air and the removal of heated air will be ensured. If the generator is placed, for example, in a basement or pantry, it will overheat, even if there is an open window. As a result, the generator will break down.

Noise protection

When installing a diesel generator or gas generator, make sure that the base on which the unit is installed is not rigidly connected to the building. It is advisable to install the generator on shock absorbers, the simplest of which can be a conventional rubber gasket.

The noise coming from the surface of the generator is reduced by means of noise protection covers. Factory-made casings work most efficiently - special containers in which sound and vibration insulating materials are used and supply and exhaust ventilation, providing the necessary normal operation generator temperature.

You can make a container yourself, but this is not as simple as it might seem at first glance. Mainly - because of the need to ensure effective ventilation.

Container for gasoline generator. Air is forced through the lower air duct closer to the engine.

Noise coming from exhaust gases, reduce with silencers. But manufacturers are prohibited from installing additional mufflers, and making any changes to the design will void the warranty. Installing a silencer can result in reduced power and difficult starting. Moreover, it is not the most effective method noise control, because sounds arise not only from the operation of the engine, but also from vibration. Therefore, it would be wiser to pay more attention to the place where the generator is installed. In a room or casing, walls are recommended to be upholstered with a special soundproof material- in one or two layers, depending on how noisy the generator is.

grounding

• metal rod with a diameter of at least 15 mm, a length of at least 1.5 m;
• a metal pipe with a diameter of at least 50 mm, a length of at least 1.5 m;
• a sheet of galvanized iron with a size of at least 500x1000 mm.

Any grounding conductor must be immersed in the ground to constantly wet soil layers. Grounding conductors must be equipped with clamps or other devices that ensure a reliable contact connection of the ground wire with the grounding conductor. The opposite end of the wire is connected to the generator ground terminal.

Exhaust gas outlet

The problem is that the extension of the exhaust pipe, as well as the additional muffler, creates additional resistance to the exit of the exhaust gases. This significantly affects engine power, durability and fuel consumption. The resistance to the release of exhaust gases from the cylinder causes incomplete combustion of the fuel, an increase in the operating temperature of the exhaust gases, and the formation of soot. Typically, manufacturers of gas generators prohibit extending the exhaust pipe and installing an additional muffler. To minimize the resistance to the exhaust outlet, the following principles should be followed:

• The inner diameter of the pipe must be larger than the diameter of the generator exhaust pipe. The more (within reason) the better. And the longer the pipe, the larger the diameter should be.
• The length of the work should be as short as possible.
• Must be least amount bends.
• The curves should be as smooth as possible.

Parts of the exhaust system must not be located near wood or other combustible materials. To reduce the room temperature, it is necessary to use non-flammable thermal insulation materials. Layer insulating material, wrapped around the piping, can significantly reduce heat radiation into the room from the exhaust system. Thermal insulation The exhaust pipe is especially important when the generator is running in a wooden container.

A corrugated stainless steel hose installed between the generator exhaust pipe and the rest of the pipeline reduces the transmission of vibration from the engine to the pipeline and building, and compensates for the forces resulting from thermal expansion. The design of the flexible section must allow displacement of either end in any direction without damage. The piping must not rest on the exhaust pipe of the generator.

The exhaust system must be equipped with a condensate trap with a condensate drain, located in the lowest part of the pipe inside the room. Or a corrugated stainless steel hose should have a bend below the level of the generator exhaust pipe, in order to prevent street condensate from entering the generator.

The outlet must be under a canopy to prevent atmospheric precipitation from entering the system. It is also recommended that restrictions be placed on children's access to outer pipe, as the temperature and composition of the exhaust gases can pose a threat to their health.

In the hole in the wall through which the pipe passes to the street, insulation must be provided from high temperature pipes and to absorb vibration.

Neglect in the removal of exhaust gases can cause death. Here are some examples:

"Dead 14-year-old girls were found in a private residential building, poisoned carbon monoxide. The cause of death was a portable diesel generator. One of the girls, in the absence of her parents, invited two girlfriends and, since the power supply was turned off in the house, she turned on the diesel generator on her own. As a result of a violation of the operating technique, three children suffocated from carbon monoxide.

"The family who died in the village of South Koryaki suffocated because of the working diesel generator, whose exhaust gases were in the house. To use an alternative source of electricity for the family forced long shutdowns of electricity. As already reported, after the cyclone, part of the Elizovsky district remained without electricity and people saved from the cold, and only today the whole family, consisting of two sons, consisted Of which he was a minor, mother, father and their close relative, neighbors found without signs of life. "

"According to preliminary data, on the evening of February 12, the men decided to take a steam bath in wood-burning bath. Her 65-year-old Kurchatovian settled in basement your garage. The bathhouse was lit by a gasoline generator. Steam room lovers started the generator and began to put firewood into the firebox. The door was closed and the exhaust gases from the gasoline generator quickly filled closed room garage. 50-year-old Kurchatov became ill. He fell in the waiting room - suffocated with carbon monoxide. The owner of the garage, feeling the lack of oxygen, rushed to the garage door to open it. But he didn't manage to do it. Having lost consciousness, the man fell on the threshold and also suffocated. The next day, relatives of the Kurchatovites, worried about their long absence, opened the garage and, finding two corpses there, called the police.

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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 a rated voltage of 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 currents earth fault (single-phase earth fault current greater than 500 A) and installations with low earth fault currents (single-phase earth fault current 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.