High impedance grounded networks
In high impedance networks the neutral of the system transformers are connected to the
ground through high impedance, mostly a reactance in parallel with a high resistor.
This type of network is many times operated in radial, but can also be found operating
meshed.
Typically, for this type of network is that the magnitude of the ground fault current is very
low compared to the short circuit current. The voltage on the healthy phases will get a
magnitude of √3 times the phase voltage during the fault. The zero sequence voltage (3U0)
will have the same magnitude in different places in the network due to low voltage drop
distribution.
The magnitude of the total fault current can be calculated according to the formula below:
EQUATION1271 V3 EN (Equation 191)
Where:
3I0 is the ground-fault current (A)
IR is the current through the neutral point resistor (A)
IL is the current through the neutral point reactor (A)
IC is the total capacitive ground-fault current (A)
The neutral point reactor is normally designed so that it can be tuned to a position where
the reactive current balances the capacitive current from the network that is:
EQUATION1272 V1 EN (Equation 192)
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 281
Application manual
To Next Page
Loading...
