Functions
2.6 Negative Sequence Protection 46
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
115
2.6.3 Setting Notes
General
The function type has been specified during configuration of the protection functions (see Section 2.1.1.2,
address 140, 46). If only the definite time elements are desired, the address 46 should be set to Definite
Time. Selecting 46 = TOC IEC or TOC ANSI in address 140 will additionally make all parameters available
that are relevant for the inverse time characteristics. If this function is not required, then Disabled is set.
The function can be turned ON or OFF in address 4001 FCT 46.
The default pickup settings and delay settings are generally sufficient for most applications. If data is available
from the manufacturer regarding the allowable long-term load imbalance and the allowable load imbalance per
unit of time, this data should be used preferentially. It is important to note that the manufacturer's data relate to
the primary values of the machine, for example, the maximum permissible permanent inverse current is re-
ferred to the nominal machine current. For the setting values at the protection device, this information is con-
verted to the secondary inverse current. The following applies
with
I
2 perm prim
permissible thermal inverse current of the motor
I
Nom Motor
Nominal Motor Current
I
CT sec
Secondary Nominal Current of the Current Transformer
I
CT prim
Primary nominal current of the current transformer
Definite Time Elements
The unbalanced load protection function comprises two elements. Therefore, the upper Element (address
4004 46-2 PICKUP) can be set to a short time delay4005 46-2 DELAY) and the lower Element (address
4002 46-1 PICKUP) can be set to a somewhat longer time delay (address 4003 46-1 DELAY). This allows
the lower Element to act, e.g. as an alarm, while the upper Element will cut the inverse time Curve as soon as
high inverse currents are present. If 46-2 PICKUP is set to about 60%, tripping is always performed with the
thermal Curve. On the other hand, with more than 60% of unbalanced load, a two-phase fault can be assumed.
The delay time 46-2 DELAY must be coordinated with the system grading of phase-to-phase faults. If power
supply with current I is provided via just two phases, the following applies to the inverse current:
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