Transformer Neutral-Point Protection Tnp; Ground Fault Location - Siemens SIPROTEC 4 Manual

Functions
2.12 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
2.12.3.3

Transformer Neutral-Point Protection TNP

General Information
The function analyzes low fault currents. The transformer neutral-point current ΙE2 measured on the 4th
current input is used as an input variable. You can find a connection example in the Appendix
Examples for Current and Voltage
If you use the function TNP, you must set the connection type (CT Connect., address 251 ) to A,G2,C,G;
G->B or A,G2,C,G; G2->B.
The Transformer neutral-point protection works in a non-directional way with an inverse-time logarithmic-
inverse knee-point characteristic curve (). The pickup current of the function and the course of the character-
istic curve can be set. You can find information on the setting values in Section
Logic
The following figure shows the logic diagram of the function TNP.
[7sj80-lo-tss, 2, en_US]
Figure 2-80
2.12.4

Ground Fault Location

Application Example
Directional determination may often be used to locate ground faults. In radial systems, locating the ground
fault is relatively simple. Since all feeders from a common bus
current, nearly the total ground fault current of the system is available at the measuring point of the faulty line
in the ungrounded system. In the resonant grounded system it is the residual wattmetric current of the
Petersen coil that flows via the measuring point. Therefore, on the faulty cables a clear "forward" decision is
made whereas in other feeders either "reverse" direction is sent back or no measurement is carried out in case
ground current is too low. Definitely the faulty line can be determined clearly.
184
Transformers,
Logic of the Ground-Fault Detection for a Transformer with Grounded Neutral Point
Figure C-12).
(Figure 2-81) deliver a capacitive charging
E50417-G1140-C343-A8, Edition 12.2017
(C.1 Connection
2.12.5 Setting Notes.
SIPROTEC 4, 7SJ80, Manual