Two-Phase Overcurrent Protection (Only Non-Directional); Setting Notes - Siemens 7SC80 Manual

Internal indication
51N PU
(All pickups)
In the trip signals, the element which initiated the tripping is also indicated.

Two-phase Overcurrent Protection (Only Non-Directional)

2.2.11
The 2-phase overcurrent protection functionality is used in isolated or grounded systems where interaction
with existing 2-phase protection equipment is required. As an isolated or grounded system remains opera-
tional with a 1-phase ground fault, this protection serves to detect double ground faults with high ground
fault currents. The respective feeder must be switched off only in this case. A 2-phase measurement is suffi-
cient for this purpose. In order to ensure selectivity of the protection in this section of the system, only phases
A and C are monitored.
If 250 50/51 2-ph prot (settable at P.System Data 1) is set to ON, Ι
ison. If the fault is a simple ground fault in B, no tripping occurs. Only if tripping occurs on A or C, is a double
ground fault assumed. This leads to pickup, and after expiry of the time delay, to tripping.
NOTE
i
i
With inrush detection activated and inrush only on B, no cross blocking will take place in the other phases.
On the other hand, if inrush with cross blocking is activated on A or C, B will also be blocked.

Setting Notes

2.2.12
General
When selecting the overcurrent protection in DIGSI, a dialog box opens with several tabs for setting the indi-
vidual parameters. Depending on the functional scope specified during configuration of the protection func-
tions at addresses 112 Charac. Phase and 113 Charac. Ground, the number of tabs can vary. If address
FCT 50/51 was set to Definite Time or Charac. Ground was set to Definite Time, then only the
settings for the definite time overcurrent protection are available. When selecting TOC IEC or TOC ANSI or
Recloser Curves or User Defined PU, inverse time characteristics are additionally available.
The superimposed high-current elements 50-2, 50-3, and 50N-2, 50N-3 are available in all these cases.
Parameter 250 50/51 2-ph prot can also be set to activate two-phase overcurrent protection.
At address 1201 FCT 50/51, overcurrent protection for phases and under address 1301 FCT 50N/51N, the
ground overcurrent protection can be switched ON or OFF.
Pickup values, time delays, and characteristics for ground protection are set separately from the pickup values,
time delays and characteristics associated with phase protection. Because of this, relay coordination for
ground faults is independent of relay coordination for phase faults, and more sensitive settings can often be
applied to directional ground protection.
Measurement Methods
The comparison values to be used for the respective element can be set in the setting sheets for the elements.
•
Measurement of the fundamental harmonic (standard method):
This measurement method processes the sampled values of the current and filters in numerical order the
fundamental harmonic so that the higher harmonics or transient peak currents remain largely unconsid-
ered.
•
Measurement of the true RMS value
The current amplitude is derived from the sampled values in accordance with the definition equation of
the true RMS value. This measurement method should be selected when higher harmonics are to be
considered by the function (e.g. in capacitor banks).
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017
Figure
51N picked up
50(N)/51(N) PU
2.2 Overcurrent Protection 50, 51, 50N, 51N
Output indication
is not used for threshold compar-
B
Functions
FNo.
1837
1761
87