Siemens 7SC80 Manual page 263

With regard to a ground fault in a ungrounded or resonant-grounded system, nearly the entire displacement
voltage appears at the device terminals, therefore the pickup setting is not critical, and typically lies between
30 V and 60 V (for 64-1 VGND with a standard V
fault resistances may require higher sensitivity (i.e. a lower pickup setting).
With regard to a grounded system, a more sensitive (lower) pickup value may be set, but it must be above the
maximum anticipated displacement voltage during normal (unbalanced) system operation.
Pickup of just the voltage element may initiate time delayed tripping assumed that ground fault detection is
configured to perform tripping (address 3101 Sens. Gnd Fault = ON or ON with GF log) and moreover
address 3130 PU CRITERIA is configured Vgnd OR INs. The tripping delay is then set at address 3112
64-1 DELAY. It is important to note that the total tripping time consists of the displacement voltage meas-
urement time (about 50 ms) plus the pickup time delay (address 3111 T-DELAY Pickup) plus the tripping
time delay (address 3112 64-1 DELAY).
Direction Determination for cos-φ/ sin-φ
Addresses 3115 to 3126 are important for direction determination.
Address 3115 67Ns-2 DIRECT determines the direction of the definite high-set current element 50Ns-2 and
can be set to either Forward or Reverse or Non-Directional, i.e. to both directions. The direction of the
current element 50Ns-1 or 51Ns can be set to Forward or Reverse or Non-Directional, i.e. to both
directions, at address 3122 67Ns-1 DIRECT..
The elements operate non-directional for voltage connection types where no measurement or calculation of
V or 3V is possible. Section
N 0
Current value RELEASE DIRECT. (address 3123) is the release threshold for directional determination. It is
based on the current components which are perpendicular to the directional limit lines. The position of the
directional limit lines themselves are based on the settings entered at addresses 3124 and 3125.
The following applies to the determination of direction of ground faults: The pickup current 3Ι0 DIR. (=
RELEASE DIRECT. address 3123) must be set as high as possible to avoid false pickup of the device
provoked by asymmetrical currents in the system and by current transformers (especially in the Holmgreen
circuit).
If direction determination is used in connection with one of the ground current elements discussed above
(50Ns-1 PICKUP, addresses 3117 ff or 51Ns PICKUP, addresses 3119 ff), only a value smaller than or
equal to the pickup value above is reasonable for RELEASE DIRECT..
A corresponding message (reverse, forward, or undefined) is issued upon direction determination. To avoid
chatter for this message resulting from extremely varying ground connection currents, a dropout delay RESET
DELAY, entered at address 3126, is initiated when directional determination drops out, and the message is
held for this period of time.
When address 3124 PHI CORRECTION is set to 0.0°, in address 3125 the following signifies
•
MEAS. METHOD = COS φ
the resistive component of the ground current with respect to the displacement voltage is most relevant
for the current value RELEASE DIRECT. (3Ι0 DIR.),
MEAS. METHOD = SIN φ
the reactive (capacitive) component of the ground current with respect to the displacement voltage is
most relevant for the current value RELEASE DIRECT. (3Ι0 DIR.)
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
-connection) or 50 V and 100 V (for 64-1 VGND). Large
0
2.1.3.2 Setting Notes gives information on this topic.
2.13 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
(Figure 2-95).
Functions
263