Functions
2.7 Negative Sequence Protection 46
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
157
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 characteristic is selected. This means that a pickup will only occur if an un-
balanced 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).
ANSI Curves (Inverse Time Tripping Curve)
Behavior of a machine due to negative sequence current can be closely replicated by means of an inverse time
tripping curve. In address
4007
the
46 ANSI CURVE
, select out of four ANSI 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 characteristic is selected. This means that a pickup will only occur if an un-
balanced load of about 1.1 times the setting value is present. If
Disk Emulation
was selected at address
4011
46-TOC RESET
, reset will occur in accordance with the reset curve as described in the Functional De-
scription.
The unbalanced load value is set at address
4008
46-TOC PICKUP
. The corresponding time multiplier is ac-
cessible via address
4009
46-TOC TIMEDIAL
.
The time multiplier can also be set to
∞
. In this case, the element will not trip after pickup. However, pickup, will
be signaled. If the inverse time element is not required at all, address
140
46
should be set to
Definite Time
during configuration of the protection functions (Section 2.1.1.2).
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