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2.13
Dir. Intermittent earth fault protection
The directional intermittent ground fault protection is designed to selectively detect intermittent ground faults in
compensated cable systems.
Intermittent ground faults in compensated cable systems are usually characterized by the following properties:
-Very short high ground current pulses (up to several hundred amperes) with a duration of less than 1 ms;
- They are self-extinguishing and re-ignite within one half period up to several periods, depending on the power
system conditions and the fault characteristic.
-Tthey can persist over longer periods (many seconds to minutes) and develop into static faults.
Such intermittent ground faults are frequently caused by weak insulation, e.g. due to decreased water resis-
tance of old cables.
Ground fault functions based on fundamental component measured values are primarily designed to detect
static ground faults and do not always operate correctly in the event of intermittent ground faults. The function
described here evaluates specifically the ground current pulses and puts them into relation with the displace-
ment voltage to determine the direction.
Applications
• Directional protection against intermittent ground faults which occur, e.g. in cables due to poor insulation or
water ingress in cable joints.
2.13.1
Description
Activating the Function
The function is only available if the device is equipped with a sensitive ground current input.
For voltage connection 213 VT Connect. 3ph = Vab, Vbc or Vab, Vbc, Vx and for 250 50/51 2-ph
prot = ON, the directional intermittent ground fault protection is ineffective. V0 cannot be formed for these con-
nection types.
The function is blocked in case of a measuring voltage failure under the condition that the fuse-failure monitor
is configured for the functioning in a grounded system (see Chapter 2.10.1, Fuse-Failure Monitor).
Furthermore, the function can be blocked externally using the binary input signal „>dIEF block".
Measurand Acquisition
The intermittent ground fault current 3I0 is measured exclusively via the sensitive ground current input INs (4th
current transformer input) of the device.
Also the displacement voltage Ven or 3 · V0 is required to determine the direction. The displacement voltage
Uen can be applied directly to the device, or the summation voltage 3 · V0 can be calculated from the three
phase-to-ground voltages.
If the displacement voltage is calculated, then:
3 · V
= V
+ V
0
A
If the displacement voltage is directly applied to the device, then V
not affected by parameter Vph / Vdelta (address 206).
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
+ V
B
C
2.13 Dir. Intermittent earth fault protection
is the voltage at the device terminals. It is
0
Functions
213
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