Overcurrent Stages Ιp, 3Ι0p for inverse-time O/C protection with ANSI characteristic
In the case of the inverse time overcurrent stages, various characteristics can be selected, depending on the
ordering version of the device and the configuration (address 126). With ANSI characteristics (address 126
Back-Up O/C = TOC ANSI) the following options are available in address 2661 ANSI Curve:
Inverse,
Short Inverse,
Long Inverse,
Moderately Inv.,
Very Inverse,
Extremely Inv. and
Definite Inv..
For the setting of the current thresholds Ip> (address 2640) and 3I0p PICKUP (address 2650) the same
considerations as for the overcurrent stages of the definite time protection (see above) apply. In this case, it
must be noted that a safety margin between the pickup threshold and the set value has already been incorpo-
rated. Pickup only occurs at a current which is approximately 10 % above the set value.
For the setting of the current thresholds Ip> (address 2640) and 3I0p PICKUP (address 2650), the same
considerations as for the overcurrent stages of the definite time protection (see above) apply. In this case, it
must be noted that a safety margin between the pickup threshold and the set value has already been incorpo-
rated. Pickup only occurs at a current which is approximately 10°% above the set value.
The above example shows that the maximum expected operating current may directly be applied as setting
here.
Primary: Set value ΙP = 630 A,
Secondary: Setting value ΙP = 5.25 A, d.h. (630 A/600 A) · 5 A.
The time multiplier to be set Time Dial TD Ip (address 2643) results from the grading coordination chart
created for the system.
The time multiplier setting TimeDial TD3I0p (address 2653) can usually be set smaller according to a sepa-
rate earth fault grading plan. If only the phase currents are to be monitored, set the pickup value of the earth
fault stage to ∞.
In addition to the inverse-time delays, a delay of constant length can be set, if necessary. The settings T Ip
Add (address 2646 for phase currents) and T 3I0p Add (address 2656 for ground current) are added to the
times of the set characteristic curves.
The parameter I(3I0)p Tele/BI (address 2670) defines whether the time delays Time Dial TD Ip
(address 2643), including the additional delay T Ip Add (address 2646), and TimeDial TD3I0p (address
2653), including the additional delay T 3I0p Add (address 2656), can be bypassed by the binary input
>O/C
InstTRIP
(No. 7110). The binary input (if allocated) is applied to all stages of the time-overcurrent protec-
tion. With I(3I0)p Tele/BI = YES you define that the IP stages trip without delay after pickup if the binary
input was activated. For I(3I0)p Tele/BI = NO the set delays are always active.
If the ΙP stage, when switching the line onto a fault, is to retrip without delay or with a short delay SOTF
Time DELAY (address 2680, see above under side title “General”), set parameter I(3I0)p SOTF (address
2671) to YES. We recommend, however, not to choose the sensitive setting for the fast tripping as switching
onto a fault typically causes a solid short circuit. It is important to avoid that the selected stage picks up due to
transients during line energization.
Additional stage Ιph>>>
When using the Ι>>> stage as stub fault protection, the pickup values Iph> STUB (address 2630) and 3I0>
STUB (address 2632) are usually not critical since the protection function is only activated when the line
isolator is open, which implies that each measured current should be a fault current. With a 1
1
/
2
circuit breaker
arrangement, however, it is possible that high short circuit currents flow from busbar A to busbar B or to
feeder 2 via the current transformers. These currents could cause different transformation errors in the two
current transformer sets Ι
A
and Ι
B
, especially in the saturation range. The protection should therefore not be
set unnecessarily sensitive. If the minimum short circuit currents on the busbars are known, the pickup value
Iph> STUB is set somewhat (approx. 10 %) below the minimum two-phase short-circuit current, 3I0> STUB
Functions
2.3 Overcurrent protection (optional)
SIPROTEC 4, 7VK61, Manual 79
C53000-G1176-C159-5, Edition 05.2018
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