Functions
2.11 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
198
Note
Please not that under address 213 VT Connect. 3ph the connection type of the voltage transformer Van,
Vbn, Vcn or Vab, Vbc, VGnd must be set. Additionally, adjustment factor Vph / Vdelta for the displace-
ment voltage must be set correctly under address 206. Depending on the type of connection of the current
transformer, the primary and secondary rated current in the ground path must be set under address 217 and
218, and, if required, the primary and secondary rated current of the second ground current transformer must
be set under address 238 and 239.
Overcurrent Elements Definite Time/Inverse Time
A two-element current/time Curve can be set at addresses 3113 to 3120. These elements operate with the
amounts of the ground current. They are therefore only useful where the magnitude of the ground current and
maybe its direction can be used to specify the ground fault. This may be the case for grounded
systems (solid
or low-resistant) or on electrical machines
connected to the busbar of an ungrounded power system, when in
case of a network ground fault the machine supplies only a negligible ground fault current across the measure-
ment location, which must be situated between the machine terminals and the network, whereas in case of a
machine ground fault the total ground fault current produced by the total network is available.
User-defined Curve (Inverse Time)
User-defined characteristics are only used for the standard measurement method cos ϕ / sin ϕ (address
130 S.Gnd.F.Dir.Ch). During configuration of a user-defined Curve, it should be noted that there is a safety
factor of approx. 1.1 between pickup and setting value - as is standard for inverse curves. This means that
pickup will only be initiated when current of 1.1 times the setting value flows.
The value pairs (current and time) are entered as multiples of the values at addresses 3119 51Ns PICKUP
and 3120 51NsTIME DIAL. Therefore, it is recommended that these addresses are initially set to 1.00 for sim-
plicity reasons. Once the curve has been entered, the settings at addresses 3119 and/or 3120 can be modified
if necessary.
The default setting of current values is ∞. They are, therefore, not enabled — and no pickup or tripping of these
protective functions will occur.
Up to 20 value pairs (current and time) may be entered at address 3131 M.of PU TD. The device then
approximates the Curve, using linear interpolation.
The following must be observed:
• The value pairs should be entered in increasing sequence. If desired, fewer than 20 pairs can be entered.
In most cases, about 10 pairs is sufficient to define the Curve accurately. A value pair which will not be used
has to be made invalid by entering "∞” for the threshold! The user must ensure that the value pairs produce
a clear and constant Curve
The current values entered should be those from Table 2-10, along with the matching times. Deviating
values I/I
p
are rounded. This, however, will not be indicated.
Current below the current value of the smallest
curve point will not lead to an extension of the tripping time.
The pickup curve (see Figure 2-73) continues, from the smallest
current point parallel to the current axis.
Current flows greater than the highest
current value entered will not result in a reduced tripping time. The
pickup curve (see Figure 2-73) continues, from the largest
current point parallel to the current axis.
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