Siemens Siprotec 7VK61 Manual page 77

function as energizing of the line on to a fault should cause a large fault current. It is important to avoid that the
selected stage picks up due to transients during line energization.
Overcurrent StagesI , 3I
P
In the case of the inverse overcurrent stages, various characteristics can be selected, depending on the order-
ing version of the device and the configuration (address 126), With the ANSI characteristics (address 126
Back-Up O/C = TOC ANSI), the following options are available at 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.
The above example shows that the maximum expected operating current may directly be applied as setting
here.
Primary: Set value IP = 630 A,
Secondary: Setting value IP = 5.25 A, i.e. (630 A/600 A) X 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 sep-
arate 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 current-dependent delays, a delay of constant length can be set, if necessary. The setting T
Ip Add (address 2646 for phase currents) and T 3I0p Add (address 2656 for earth currents) are in addition
to the time delays resulting from the set curves.
The parameter I(3I0)p Tele/BI (address 2670) defines whether the time delays Time Dial TD Ip (ad-
dress 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 protection.
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 IP stage, when switching the line on to a fault, is to trip without delay or with a short delay, SOTF Time
DELAY (address 2680, see above under margin heading „General"), the parameter I(3I0)p SOTF (address
2671) is set to YES. We recommend, however, not to choose the sensitive setting for the switch on to a fault
function as energizing of the line on to a fault should cause a large fault current. It is important to avoid that the
selected stage picks up due to transients during line energization.
Additional stage I >>>
ph
When using the I>>> stage as a stub protection, the pickup values Iph> STUB (address 2630) and 3I0>
STUB (address 2632) are mostly not critical since the protection is only to be active when the line isolator is
open where each current should be a fault current. With a 1
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009
for inverse time overcurrent protection with ANSI characteristics
0P
2.3 Overcurrent protection (optional)
1
/ circuit breaker arrangement, however, it is pos-
2
Functions
77