Siemens siprotec 7SA522 User Manual page 291

Inverse Time Over-
current Stages
IP, 3I0P
with IEC–curves
7SA522 Manual
C53000-G1176-C119-2
In the case of the inverse time overcurrent stages, various characteristics can be se-
lected, depending on the version of the device and the configuration (Section 5.1, ad-
dress ). For the IEC–curves (address  %DFN8S 2& = 72& ,(&) the fol-
lowing 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 10.9).
For the setting of the current thresholds ,S! (address ) and ,S 3,&.83 (ad-
dress ) 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 be-
tween 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 grad-
ing plan applicable to the network. If implemented as emergency overcurrent protec-
tion, shorter tripping times are advisable (one grading time step 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 de-
lay 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
$GG (address ). The binary input (if it is assigned) is common to all stages of the
overcurrent protection. With the setting , , S 7HOH%, = <HV it is therefore de-
termined that the I –stage trips without delay following pick-up if an operate signal is
P
present at the binary input; with the setting , , S 7HOH%, = 1R the set time de-
lays always come into effect.
If the IP-stage is to trip when switching the line on to a fault without or with a short de-
lay, 627) 7LPH '(/$< (address , see above and refer to Sub-section "Gener-
al"), the parameter , , S 627) (address ) is set to Yes. We recommend,
however, not to choose the sensitive setting for the switch on to fault function as en-
ergyzing 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.
Functions
6-143