电力系统的接地形式(图示)
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N
= N eutral Conductor
PE
= P rotection- E arth Conductor PEN
= P rotectitive- E arth- N eutral- Conductor T
= T erre = Earthing I
= I solation S
= S eparated Neutral and Protective Conductor C
= C ombined Neutral and Protective Conductor Abb. 6 TN-S-System
Abb. 7 TN-C System Abb. 8 TN-C-S System Abb.9 TT System Abb. 10 IT System
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). 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):
TN-S-system
- Separated neutral and protective conductor in the entire network (diagram 6)TN-C-system
- Functions of neutral and protective conductor are combined in the entire network in one conductor, the PEN- conductor (diagram 7).TN-C-S-system
- 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).
The IT-system has no direct connection between active conductors and earthed parts. The elements of the electrical machine are earthed (diagram 10).