电力系统的接地形式(图示)

N

PE

PEN

T

I

S

C

= N eutral Conductor

= P rotection- E arth Conductor = P rotectitive- E arth- N eutral- Conductor = T erre = Earthing = Isolation = S eparated Neutral and Protective Conductor = C ombined Neutral and Protective Conductor Network configuration Power systems Network configuration Network configurations are differed as per kind of – direct current, alternating current – “number of active conductors and the kind of earth connection” using the following characters: First letter: earthing of the current source (part 300, VDE 0100): T – direct earthing of a point I - insulation of all active parts of earth

or connection of a point with the earth via an impedance. Second letter: earthing of elements of electrical machine:

T – element is directly earthed, independent of the earthing of a point of a current source

N – element is directly connected to the operating earth electrode

(in networks of alternating voltage the earthed point is mostly the neutral point).

Further letters: arrangement of neutral conductor and protective conductor in the TN-system:

S – functions of neutral and protective conductor by separate conductors

C – functions of neutral and protective conductor combined in one conductor (PEN). Abb. 6 TN-S-System

Abb. 7 TN-C System In TN-systems a point is directly earthed (operating earth

electrode). The elements of the electrical machine are connected to this point via PE- or PEN-conductor.

Three types of TN-systems are to be differed (part 300, VDE 0100):

Abb. 8 TN-C-S System TN-S-system

TN-C-system

TN-C-S-system

Abb.9 TT System - Separated neutral and protective conductor in the entire network (diagram 6)- Functions of neutral and protective conductor are combined in the entire network in one conductor, the PEN- conductor (diagram 7).- In one part of the network the neutral and the protective conductor are combined (PEN-

conductor) (diagram 8).

In the TT-system a point is directly earthed (operating earth electrode). The elements of the electrical machine are connected with earth electrodes, that are separated from the operating earth electrode (diagram 9).

Abb. 10 IT System

The IT-system has no direct connection between active conductors and earthed parts. The elements of the electrical machine are earthed (diagram 10).