Siemens 7SC80 Manual page 260

Functions
2.13 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
is created. A ground fault log is created for ON with GF log and Alarm Only. Setting ON with GF log
is only available if characteristic V0/I0 φ mea. has been selected at address 130 S.Gnd.F.Dir.Ch.
The parameters 3111 T-DELAY Pickup and 3130 PU CRITERIA are only visible if the standard measure-
ment method cos φ / sin φ has been selected when setting the direction characteristic. The ground fault
is detected and reported when the displacement voltage was sustained a certain time T-DELAY Pickup).
Address 3130 PU CRITERIA specifies whether ground fault detection is enabled only for pickups of V
(Vgnd AND INs) or as soon as one of the two has picked up (Vgnd OR INs).
The pickup can be stabilized for ground fault protection with definite time curve by a settable dropout time
delay (address 3121 50Ns T DROP-OUT). This facility is used in power systems with intermittent faults. Used
together with electro-mechanical relays, it allows different dropout responses to be adjusted and time grading
of digital and electro-magnetic relays to be implemented. The setting depends on the dropout time delay of
the electro-magnetic relay. If no coordination is required, the preset value (zero = no dropout time delay)
remains.
Overcurrent Elements Definite Time/Inverse Time
A two-element current/time characteristic 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 measurement 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.
IEC/ANSI characteristics
For an inverse time element 51Ns, a characteristic according to IEC or ANSI standards may be used. These
characteristics can be employed for the measurement method cos φ / sin φ.
The type of IEC characteristic can be selected under address 3144 51Ns IEC CURVE. Setting options that can
ve selected are Normal Inverse, Very Inverse, Extremely Inv. and Long Inverse.
The type of ANSI characteristic can be selected under address 3145 51Ns ANSI CURVE. Setting options that
can be selected are Very Inverse, Inverse, Short Inverse, Long Inverse, Moderately Inv.,
Extremely Inv. and Definite Inv..
As dropout time, set under address 3146 51Ns Drop-out Instantaneous or Disk Emulation.
User-defined characteristic (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 characteristic, 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
simplicity reasons. Once the curve has been entered, the settings at addresses 3119 and/or 3120 can be modi-
fied 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 characteristic, using linear interpolation.
260 SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
and
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