Section 1 General Rules

Grounding and protective measures for electrical safety. Grounding devices of electrical installations with voltage up to 1 kV in networks with dead-earthed neutral

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

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1.7.100. In electrical installations with a solidly grounded neutral, the neutral of a three-phase alternating current generator or transformer, the midpoint of a direct current source, one of the terminals of a single-phase current source must be connected to the ground electrode using a ground conductor.

An artificial earth conductor intended for neutral earthing should, as a rule, be located near the generator or transformer. For intrashop substations, it is allowed to place the ground electrode near the wall of the building.

If the foundation of the building in which the substation is located is used as natural grounding conductors, the transformer neutral should be grounded by attaching at least two metal columns or to embedded parts welded to the reinforcement of at least two reinforced concrete foundations.

When the built-in substations are located on different floors of a multi-storey building, the neutral grounding of the transformers of such substations must be carried out using a specially laid grounding conductor. In this case, the grounding conductor must be additionally connected to the building column closest to the transformer, and its resistance is taken into account when determining the spreading resistance of the grounding device to which the transformer neutral is connected.

In all cases, measures must be taken to ensure the continuity of the ground circuit and to protect the ground conductor from mechanical damage.

If a current transformer is installed in the PEN conductor connecting the neutral of the transformer or generator to the PEN bus of the switchgear with voltage up to 1 kV, then the grounding conductor must not be connected directly to the neutral of the transformer or generator, but to the PEN conductor, if possible immediately after the transformer current. In this case, the separation of the PEN conductor into PE and N conductors in the TN-S system must also be carried out behind the current transformer. The current transformer should be placed as close as possible to the neutral terminal of the generator or transformer.

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 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 of natural grounding conductors, as well as grounding conductors for repeated grounding of a PEN or PE conductor of an overhead line with a voltage of up to 1 kV with a number of outgoing lines of at least two. The resistance of the ground electrode located in close proximity to 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 V of a single-phase current source current.

With a specific earth resistance ρ > 100 Ohm m, it is allowed to increase the indicated norms by 0,01 ρ times, but not more than tenfold.

1.7.102. At the ends of overhead lines or branches from them longer than 200 m, as well as at the inputs of overhead lines to electrical installations, in which automatic power off is applied as a protective measure in case of indirect contact, re-grounding of the PEN conductor must be performed. In this case, first of all, natural grounding should be used, for example, underground parts of supports, as well as grounding devices designed for lightning surges (see Chap. 2.4).

The indicated repeated groundings are performed if more frequent groundings are not required under the conditions of lightning surge protection.

Re-grounding of the PEN conductor in DC networks must be carried out using separate artificial grounding conductors, which should not have metal connections with underground pipelines.

Grounding conductors for re-grounding the PEN conductor must have dimensions not less than those given in Table. 1.7.4.

Table 1.7.4. The smallest dimensions of grounding conductors and grounding conductors laid in the ground

* Diameter of each wire.

1.7.103. The total spreading resistance of ground electrodes (including natural ones) of all re-groundings of the PEN conductor of each overhead line at any time of the year should be no more than 5, 10 and 20 Ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V single-phase current source. In this case, the spreading resistance of the grounding conductor of each of the repeated groundings should be no more than 15, 30 and 60 ohms, respectively, at the same voltages.

With a specific earth resistance ρ > 100 Ohm m, it is allowed to increase the indicated norms by 0,01 ρ times, but not more than tenfold.

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

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