
Table. 5.3.5 - 78. Register content.
Register
Description
Event code
dd.mm.yyyy hh:mm:ss.mss
Date and time
5184-5389 Descr.
I
0
pre-triggering current
Start average current
I
0
fault current
Trip -20ms averages
Fault capacity I
0
Trip -20ms averages
Fault resist I
0
Trip -20ms averages
Fault U
0
(%)
Trip -20ms averages
Fault U
0
(V)
Trip -20ms averages
I
0
fault angle
0...360°
Trip time remaining
0 ms...1800s
Used SG
Setting group 1...8 active
Network GND
Unearthed, Petersen coil earthed, Earthed network
I
0
pre-fault current
Start -200ms averages
5.3.6 Intermittent earth fault protection (I0int>; 67NT)
The intermittent earth fault is a transient type of single-phase-to-earth fault where the actual fault
phenomenon lasts for about a few hundred microseconds. The intermittent earth fault is commonly
seen in Petersen coil grounded (compensated) medium voltage networks. The intermittent earth fault is
commonly thought only as a cable network problem but it can also occur in overhead line networks.
The key point for this type of fault appearance is the compensation of earth fault currents with a
Petersen coil.
This phenomenon is becoming more frequent as more utilities networks are replacing overhead lines
with cables dug into the ground. This development in distribution networks is very understandable
as overhead lines are more vulnerable to possible seasonal storm damages. Also, the annual
maintenance costs as well as the annual power-down time are both significantly lower with
underground cable networks than with overhead line networks. However, the problem at hand is
caused by the increasing amount of cabling in the network which in turn causes dramatic increases
in the capacitive earth fault currents in the distribution networks. When the capacitive earth fault
current increases in the network, it becomes necessary to detect the earth fault current with a
Petersen coil.
Problems caused by intermittent earth fault are normally seen in compensated network substations: an
earth fault can trip multiple feeders simultaneously, or an entire substation can be tripped by residual
voltage back-up protection from the incomer. This is typical of old-fashioned relay protection as it is not
capable of differentiating between a normal consistent earth fault and an intermittent earth fault. As the
intermittent earth fault is a transient type of fault where the actual fault lasts only for a few hundred
microseconds, this causes traditional directional earth fault protection relays to lose their directional
sensitivity, and as a result their directional decision algorithms go haywire and the trip decisions will be
completely random. Typically, when a whole substation goes dark the logs of all protection relays show
how they have experienced multiple incorrect directional earth fault starts and releases, as well as an
incomer relay residual voltage trip. This is also the worst case scenario. In another typical scenario a
few feeders, including the correct faulty feeder, have tripped at the same time. In this case, as in the
previous, all the relays' logs show various incorrect directional earth fault starts and releases.
A
AQ
Q-F215
-F215
Instruction manual
Version: 2.04
133
Содержание AQ-F215
Страница 1: ...AQ F215 Feeder protection IED Instruction manual ...
Страница 430: ...Figure 7 4 261 Example block scheme A AQ Q F215 F215 Instruction manual Version 2 04 429 ...
Страница 452: ...Figure 8 14 284 Panel cutout dimensions and device spacing A AQ Q F215 F215 Instruction manual Version 2 04 451 ...
Страница 487: ...10 Ordering information A AQ Q F215 F215 Instruction manual Version 2 04 486 ...