Functions
2.6 Negative Sequence Protection 46
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
117
The following fault currents may be detected at the low side:
If 46-1 PICKUP on the high side of the devices is set to = 0.1, then a fault current of I = 3 · TR
V
· TR
I
· 46-1
PICKUP = 3 · 110/20 · 100 · 0.1 A = 165 A for single-phase faults and √3
· TR
V
· TR
I
·46-1 PICKUP = 95 A
can be detected for two-phase faults at the low side. This corresponds to 36% and 20% of the transformer
nominal current respectively. It is important to note that load current is not taken into account in this simplified
example.
As it cannot be recognized reliably on which side the thus detected fault is located, the delay time 46-1 DELAY
must be coordinated with other downstream relays in the system.
Pickup Stabilization (Definite Time)
Pickup of the definite time elements can be stabilized by means of a configurable dropout time. This dropout
time is set in 4012 46 T DROP-OUT.
IEC Curves (Inverse Time Tripping Curve)
The thermal behavior of a machine can be closely replicated due to negative sequence by means of an inverse
time tripping curve. In address 4006 46 IEC CURVE, select out of three IEC curves provided by the device
the curve which is most similar to the thermal unbalanced load curve provided by the manufacturer. The tripping
curves of the protective relay, and the formulas on which they are based, are given in the Technical Data.
It must be noted that a safety factor of about 1.1 has already been included between the pickup value and the
setting value when an inverse time Curve is selected. This means that a pickup will only occur if an unbalanced
load of about 1.1 times the setting value 46-TOC PICKUP is present (address 4008). The dropout is performed
as soon as the value falls below 95% of the pickup value.
The associated time multiplier is entered at address 4010, 46-TOC TIMEDIAL.
The time multiplier can also be set to ∞. After pickup the Element will then not trip. Pickup, however, will be
signaled. If the inverse time Element is not required at all, address 140 46 should be set to Definite Time
during the configuration of protection functions (Section 2.1.1.2).
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