Varieties of grounding systems. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Grounding. Types of grounding systems. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Grounding and grounding

The classification of types of grounding systems is given as the main characteristic of the supply network. GOST R 50571.2 considers the following grounding systems: TN-C, TN-S, TN-CS, TT, IT (Figure 14.2-14.6).

В TN-C system the transformer substation has a direct connection between the transformer neutral and the ground (grounded neutral). All open conductive parts of the electrical installation of the building are directly connected to the grounding device of the transformer substation. To ensure this connection, a combined zero protective and working conductor (PEN).

Varieties of grounding systems
Rice. 14.2. TN-C system

В TN-S system the transformer substation has a direct connection of current-carrying parts with the ground. All open conductive parts of the electrical installation of the building are directly connected to the grounding device of the transformer substation. To ensure this connection, a separate zero protective conductor (PE).

Varieties of grounding systems
Rice. 14.3. TN-S system

В TN-CS system the transformer substation has a direct connection of current-carrying parts with the ground. All exposed conductive parts of the electrical installation of the building are directly connected to the grounding point of the transformer substation. To ensure this connection on the site, a transformer substation - electrical installations of the building is used combined neutral protective and working conductor (PEN), in the rest of the electrical circuit - a separate zero protective conductor (PE).

Varieties of grounding systems
Rice. 14.4. TNC-S system

В TT system the transformer substation has a direct connection of current-carrying parts with the ground. All open conductive parts of the electrical installation of the building have a direct connection to the ground through a grounding conductor, electrically independent from the neutral grounding conductor of the transformer substation.

Varieties of grounding systems
Rice. 14.5. TT system

The IT system is used, as a rule, in electrical installations of buildings and structures for special purposes.

Varieties of grounding systems
Rice. 14.6. IT system

Grounding system symbols

First letter in the designation of the earthing system defines grounding nature of the power supply:

T - direct connection of the neutral of the power source with the ground;
I - all current-carrying parts are isolated from the ground.

Second letter determines the nature of the grounding of open conductive parts of the electrical installation of the building:

T - direct connection of the open conductive parts of the electrical installation of the building with the ground, regardless of the nature of the connection between the power source and the ground;
N - direct connection of the open conductive parts of the electrical installation of the building with the grounding point of the power source.

Letters following a dash after N, determine the nature of this relationship - functional method of arranging the zero protective and zero working conductors:

S - functions of zero protective PE and zero working N conductors are provided with separate conductors;
C - the functions of the zero protective and zero working conductors are provided by one common PEN conductor.

Grounding systems used in Russia

In Russia, a system similar to TN-C is still used (Fig. 14.2). In it, the open conductive parts of the electrical installation (housings, casings of electrical equipment) are connected to the grounded neutral of the transformer substation by the combined zero protective and working conductor PEN, i.e. "zeroed". This system is relatively simple and cheap.

This system does not provide the required level of electrical safety. Three systems can be easily implemented using existing power supply networks: TN-C, TN-CS and TT.

The neutral conductor of the same overhead line (VL, cable line - KL), depending on the type of grounding system, can perform different functions. For electrical installations with the type of grounding system TN-C and TN-CS, the neutral conductor is a combined zero protective and working conductor, for electrical installations with a TT system - only a zero working conductor. In other words, depending on the type of grounding system, the same neutral conductor VL (KL) can perform the functions of both a combined zero protective and working conductor, and only a zero working conductor.

PEN split point in the TN-CS system, the zero protective and zero working conductors can be made at the entrance to the building. In accordance with GOST R 50571.3 and GOST R 50571.10, it is forbidden to combine zero protective and zero working conductors after separating the PEN conductor at the entrance to the building.

The standards also make the following requirements for the PEN conductor:

the cross section must be at least 10 mm2 for copper or 16 mm2 for aluminum;
part of the installation with a PEN conductor must not be protected by residual current devices (RCDs) that react to differential currents.

Author: Koryakin-Chernyak S.L.

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