Siemens siprotec 7SA6 - Page 333

Functions
6-1517SA6 Manual
C53000-G1176-C133-1
Inverse Time
Overcurrent Stages
IP, 3I0P
with IEC–curves
In the case of the inverse time overcurrent stages, various characteristics can be
selected, depending on the version of the device and the configuration (Section 5.1,
address ). For the IEC–curves (address  %DFN8S2& = 72&,(&) the
following are available in address  ,(&&XUYH:
,QYHUVH (
normal inverse , Type A according to IEC 60255–3),
9HU\LQYHUVH (
very inverse , Type B according to IEC 60255–3),
([WUHPHO\LQYHUVH (
extremely inverse , Type C according to IEC 60255–3), and
/RQJ7LPH,QYHUVH (
longtime , Type B according to IEC 60255–3).
The curves and equations that the curves are based on, are shown in the technical
data (Section 10.5, Figure 10-1).
For the setting of the current thresholds ,S! (address ) and ,S3,&.83
(address ) 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 pick-up threshold and the set value has already been incorporated. Pick-
up 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: Set value Ip> = 5.25 A, i.e. (630 A / 600 A) · 5 A.
The time multiplier setting 7,S7LPH'LDO (address ) is derived from the
grading plan applicable to the network. If implemented as emergency overcurrent
protection, shorter tripping times are advisable (one grading time margin above the
fast tripping stage), as this function is only activated in the case of the loss of the
local
measured voltage.
The time multiplier setting 7,S7LPH'LDO (address ) can usually be set
smaller according to a separate earth fault grading plan.
In addition to the current dependant time delay an additional constant time length
delay can be set if required. The setting 7,S$GG (address  for phase currents)
and 7,S$GG (address  for earth currents) are in addition to the time delays
resulting from the set curves.
The setting parameter ,,S7HOH%, (address ) determines if it is possible
to use the binary input “!2&,QVW75,3” (F.No. ) to bypass the trip delays 7
,S7LPH'LDO (address ) including the additional time 7,S$GG (address
) and 7,S7LPH'LDO (address ) including the additional time 7,S
$GG (address ). The binary input (if it is assigned) is common to all stages of the
overcurrent protection. With the setting ,,S7HOH%, = <HV it is therefore
determined that the I
P
–stage trips without delay following pick-up if an operate signal
is present at the binary input; with the setting ,,S7HOH%, = 1R the set time
delays always come into effect.
If the Ip-stage is to trip when switching the line on to a fault without or with a short
delay, 627)7LPH'(/$< (address , see above and refer to Sub-section
“General”), the parameter ,,S627) (address ) is set to Yes. We
recommend, however, not to choose the sensitive stage for the switch on to 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 in a transient way during line
energization.