Setting Notes - Siemens SIPROTEC 4 Manual

Setting Notes

2.7.3
General
The function type has been specified during configuration of the protection functions (see Section
2.1.1.2 Setting
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.
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 delay 4005 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 characteristic as soon
as high inverse currents are present. If 46-2 PICKUP is set to about 60%, tripping is always performed with
the thermal characteristic. 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:
[formel-i2-058-260602-kn, 1, en_US]
Examples:
When protecting feeder or cable systems, unbalanced load protection may serve to identify low magnitude
unsymmetrical faults below the pickup values of the directional and non-directional overcurrent elements.
Here, the following must be observed:
[formel-i2-058-260602-kn, 1, en_US]
A phase-to-ground fault with current Ι corresponds to the following negative sequence current:
[formel-i2-033-260602-kn, 1, en_US]
On the other hand, with more than 60% of unbalanced load, a phase-to-phase fault can be assumed. The
delay time 46-2 DELAY must be coordinated with the system grading of phase-to-phase faults.
For a power transformer, unbalanced load protection may be used as sensitive protection for low magnitude
phase-to-ground and phase-to-phase faults. In particular, this application is well suited for delta-wye trans-
formers where low side phase-to-ground faults do not generate high side zero sequence currents (e.g. vector
group Dy).
Since transformers transform symmetrical currents according to the transformation ratio "CTR", the relation-
ship between negative sequence currents and total fault current for phase-to-phase faults and phase-to-
ground faults are valid for the transformer as long as the turns ratio "CTR" is taken into consideration.
Consider a transformer with the following data:
Base Transformer Rating
Primary Nominal Voltage
Secondary Nominal Voltage
SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
Notes, address 140, 46). If only the definite time elements are desired, the address 46 should
S = 16 MVA
NomT
V = 110 kV
Nom
(TR = 110/20)
V = 20 kV
V
Nom
Functions
2.7 Negative Sequence Protection 46
135