The distance protection function is designed to meet basic requirements for application
on transmission and sub transmission lines (solid grounded systems) although it also
can be used on distribution levels.
System grounding
The type of system grounding plays an important roll when designing the protection
system. In the following sections, some hints with respect to distance protection are
highlighted.
Solid grounded networks
In solid grounded systems the transformer neutrals are connected solidly to ground
without any impedance between the transformer neutral and ground.
ANSI05000215 V1 EN
Figure 60: Solidly grounded network
The ground fault current is as high or even higher than the short-circuit current. The
series impedances determine the magnitude of the fault current. The shunt admittance
has very limited influence on the ground fault current. The shunt admittance may,
however, have some marginal influence on the ground fault current in networks with
long transmission lines.
The ground fault current at single phase -to-ground in phase A can be calculated as
equation
98:
A A
0
1 2 0 f 1 N f
3 V
3I
Z Z Z 3Z Z Z Z
V×
= =
+ + + + +
EQUATION1710 V2 EN
(Equation 98)
Where:
VA is the phase-to-ground voltage (kV) in the faulty phase before fault
Z1 is the positive sequence impedance (Ω/phase)
Z2 is the negative sequence impedance (Ω/phase)
Z0 is the zero sequence impedance (Ω/phase)
Zf is the fault impedance (Ω), often resistive
ZN is the ground return impedance defined as (Z0-Z1)/3
Section 3 1MRK504116-UUS C
IED application
190
Application manual
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