Section 1 General Rules

Grounding and protective measures for electrical safety. Grounding devices for electrical installations with voltages above 1 kV in networks with effectively grounded neutral

Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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1.7.88. Grounding devices of electrical installations with voltages above 1 kV in networks with an effectively grounded neutral should be made in compliance with the requirements either for their resistance (1.7.90) or for touch voltage (1.7.91), as well as in compliance with the design requirements (1.7.92 - 1.7.93) and to limit the voltage on the grounding device (1.7.89). Requirements 1.7.89 - 11.7.93 do not apply to grounding devices of overhead lines.

1.7.89. The voltage on the grounding device when the earth fault current drains from it should, as a rule, not exceed 10 kV. Voltage above 10 kV is allowed on grounding devices, from which the removal of potentials outside buildings and external fences of electrical installations is excluded. When the voltage on the grounding device is more than 5 kV, measures must be taken to protect the insulation of the outgoing communication and telemechanics cables and to prevent the removal of dangerous potentials outside the electrical installation.

1.7.90. The grounding device, which is carried out in compliance with the requirements for its resistance, must have a resistance of no more than 0,5 Ohm at any time of the year, taking into account the resistance of natural and artificial grounding conductors.

In order to equalize the electrical potential and ensure the connection of electrical equipment to the ground electrode system in the territory occupied by the equipment, longitudinal and transverse horizontal earth conductors should be laid and combined into a ground grid.

Longitudinal grounding conductors should be laid along the axes of electrical equipment from the service side at a depth of 0,5-0,7 m from the ground surface and at a distance of 0,8-1,0 m from foundations or equipment foundations. It is allowed to increase the distances from the foundations or bases of the equipment up to 1,5 m with the laying of one ground electrode for two rows of equipment, if the service sides face each other, and the distance between the bases or foundations of the two rows does not exceed 3,0 m.

Transverse ground electrodes should be laid in convenient places between equipment at a depth of 0,5-0,7 m from the ground. The distance between them is recommended to be taken as increasing from the periphery to the center of the grounding grid. In this case, the first and subsequent distances, starting from the periphery, should not exceed 4,0, respectively; 5,0; 6,0; 7,5; 9,0; 11,0; 13,5; 16,0; 20,0 m.

Horizontal grounding conductors should be laid along the edge of the territory occupied by the grounding device so that they together form a closed loop.

If the circuit of the grounding device is located within the external fence of the electrical installation, then at the entrances and entrances to its territory, the potential should be equalized by installing two vertical ground electrodes connected to an external horizontal ground electrode opposite the entrances and entrances. Vertical earthing should be 3-5 m long, and the distance between them should be equal to the width of the entrance or entrance.

1.7.91. The grounding device, which is carried out in compliance with the requirements for the contact voltage, must provide at any time of the year when the earth fault current drains from it, the contact voltage values ​​\u12.1.038b\uXNUMXbthat do not exceed the rated ones (see GOST XNUMX). In this case, the resistance of the grounding device is determined by the allowable voltage on the grounding device and the ground fault current.

When determining the value of the allowable contact voltage, the sum of the protection action time and the total switch off time should be taken as the estimated exposure time. When determining the permissible values ​​​​of contact voltage at workplaces where, during the production of operational switching, short circuits may occur on structures that are accessible to touch by the personnel performing the switching, the duration of the backup protection should be taken, and for the rest of the territory - the main protection.

The placement of longitudinal and transverse horizontal grounding conductors should be determined by the requirements for limiting contact voltages to normalized values ​​and the convenience of connecting grounded equipment. The distance between longitudinal and transverse horizontal artificial ground electrodes should not exceed 30 m, and the depth of their laying in the ground should be at least 0,3 m. -0,1 m.

In the case of combining grounding devices of different voltages into one common grounding device, the contact voltage must be determined by the highest short-circuit current to earth of the combined outdoor switchgear.

* The workplace should be understood as a place for the operational maintenance of electrical devices.

1.7.92. When making a grounding device in compliance with the requirements for its resistance or contact voltage, in addition to the requirements of 1.7.90 - 1.7.91, it should be:

• lay grounding conductors connecting equipment or structures to the ground electrode in the ground at a depth of at least 0,3 m;
• lay longitudinal and transverse horizontal grounding conductors (in four directions) near the locations of grounded neutrals of power transformers, short circuiters.

When the grounding device goes beyond the fence of the electrical installation, horizontal ground electrodes located outside the territory of the electrical installation should be laid at a depth of at least 1 m. In this case, the external contour of the grounding device is recommended to be made in the form of a polygon with obtuse or rounded corners.

1.7.93. It is not recommended to connect the external fence of electrical installations to a grounding device.

If 110 kV and higher overhead lines depart from the electrical installation, then the fence should be grounded using vertical ground electrodes 2-3 m long installed at the fence posts along its entire perimeter after 20-50 m. Installation of such ground electrodes is not required for a fence with metal posts and with those racks made of reinforced concrete, the reinforcement of which is electrically connected to the metal links of the fence.

To exclude the electrical connection of the external fence with the grounding device, the distance from the fence to the elements of the grounding device located along it from the inside, outside or on both sides must be at least 2 m. Horizontal ground electrodes, pipes and cables with a metal sheath or armor and other metal communications should be laid in the middle between the posts of the fence at a depth of at least 0,5 m. not less than 1 m.

The power supply of electrical receivers installed on the outer fence should be carried out from isolation transformers. These transformers are not allowed to be installed on the fence. The line connecting the secondary winding of the isolating transformer with the power receiver located on the fence must be isolated from the ground by the calculated voltage value at the grounding device.

If at least one of the above measures is not possible, then the metal parts of the fence should be connected to a grounding device and potential equalization should be performed so that the contact voltage on the outer and inner sides of the fence does not exceed the permissible values. When performing a grounding device according to the permissible resistance, for this purpose a horizontal grounding conductor must be laid on the outer side of the fence at a distance of 1 m from it and at a depth of 1 m. This grounding conductor should be connected to the grounding device at least at four points.

1.7.94. If the grounding device of an electrical installation with a voltage above 1 kV of a network with an effectively grounded neutral is connected to the grounding device of another electrical installation using a cable with a metal sheath or armor or other metal connections, then in order to equalize the potentials around the specified other electrical installation or the building in which it is located, it is necessary to comply one of the following conditions:

1) laying in the ground at a depth of 1 m and at a distance of 1 m from the foundation of the building or from the perimeter of the territory occupied by the equipment, a ground electrode connected to the potential equalization system of this building or this territory, and at the entrances and entrances to the building - laying conductors on a distance of 1 and 2 m from the ground electrode at a depth of 1 and 1,5 m, respectively, and the connection of these conductors to the ground electrode;

2) the use of reinforced concrete foundations as grounding conductors in accordance with 1.7.109, if this ensures an acceptable level of potential equalization. Ensuring the conditions for equalizing potentials by means of reinforced concrete foundations used as grounding conductors is determined in accordance with GOST 12.1.030 "Electrical safety. Protective grounding, zeroing".

It is not necessary to fulfill the conditions specified in paragraphs. 1 and 2, if there are asphalt pavements around the buildings, including at the entrances and at the entrances. If there is no blind area at any entrance (entrance), potential equalization must be performed at this entrance (entrance) by laying two conductors, as indicated in paragraphs. 1, or the condition according to paragraphs. 2. In this case, the requirements of 1.7.95 must be met in all cases.

1.7.95. In order to avoid potential carryover, it is not allowed to supply electrical receivers located outside the grounding devices of electrical installations with a voltage above 1 kV of a network with an effectively grounded neutral, from windings up to 1 kV with a grounded neutral of transformers located within the circuit of the grounding device of an electrical installation with a voltage above 1 kV.

If necessary, such electrical receivers can be powered from a transformer with an isolated neutral on the side with a voltage of up to 1 kV via a cable line made with a cable without a metal sheath and without armor, or via overhead lines.

In this case, the voltage on the grounding device must not exceed the operating voltage of the breakdown fuse installed on the low voltage side of the transformer with isolated neutral.

The power supply of such electrical receivers can also be carried out from an isolating transformer. The isolation transformer and the line from its secondary winding to the power receiver, if it passes through the territory occupied by the grounding device of an electrical installation with a voltage above 1 kV, must be insulated from the ground by the calculated value of the voltage at the grounding device.

See other articles Section Rules for the installation of electrical installations (PUE).

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