Siemens siprotec 7SA6 User Manual page 293

Inverse Time
Overcurrent
Stage with
IEC–Characteristic
Inverse Time
Overcurrent
Stage with ANSI–
Characteristic
7SA6 Manual
C53000-G1176-C133-1
 ,S 3,&.83 then determines the current pick-up threshold and address 
,S 0D[7'(/$< the definite time delay.
The values for the time delay settings 7 ,!!! (address ), 7 ,!! (address
) and 7 ,! (address ) are derived from the earth fault grading
coordination diagram of the system.
If the distance protection implements single-pole tripping, the earth fault protection
may be delayed by one grading margin to give preference to the phase selective
tripping by the distance protection over of the earth fault protection which always trips
three-pole. It is however also possible to block the earth fault protection with the
distance protection (See "Blocking" above).
During the selection of the current and time settings, regard must be taken of whether
a stage should be direction dependent and whether it uses teleprotection. Refer to
also to the margin headings "Direction Determination" and "Teleprotection with Earth
Fault Protection" below.
The set time delays are pure additional time delays which do not include the response
time (measuring time) of the protection.
Also for the inverse time overcurrent stage the operating mode must initially be set:
2S PRGH ,S (address ). This stage can be set to operate )RUZDUG (usually
towards line) or 5HYHUVH direction (usually towards busbar) or 1RQ'LUHFWLRQDO
(in both directions). If a particular stage is not required, set its mode to ,QDFWLYH.
For the inverse time overcurrent stage 3I
curves depending on the version of the relay and the configuration (Section 5.1,
address ) that was selected. If an inverse overcurrent stage is not required, the
address  is set to (DUWK )DXOW 2& = 'HILQLWH 7LPH. The 3I
then be used as a fourth definite time stage (refer to "Definite Time Stages" above) or
deactivated. In the case of the IEC–curves (address  (DUWK )DXOW 2& = 72&
,(&) the following alternatives are available in the address  ,(& &XUYH:
,QYHUVH ( normal inverse , Type A according to IEC 60255–3),
9HU\ LQYHUVH ( very inverse , Type B according to IEC 60255–3),
([WUHPHO\ LQY ( extremely inverse , Type C according to IEC 60255–3), and
/RQJ7LPH,QYHUVH ( longtime , Type B according to IEC 60255–3).
The curves and equations the curves are based on are illustrated in the technical data
(Section 10.5, Figure 10-1).
Similar considerations as for the definite time stages (see above) apply to the setting
of the pick-up threshold ,S 3,&.83 (address ). In this case it must be
considered that a safety margin has already been included between the pick-up
threshold and the setting value. The stage only picks up when the measured signal is
approximately 10 % above the setting value.
The time multiplier setting 7 ,S 7LPH'LDO (address ) is derived from the
grading coordination chart which was set up for earth faults in the system.
In addition to the inverse current dependant time delay, a constant (fixed length) time
delay can also be set if this is required. The setting $GG7'(/$< (address ) is
added to the time of the set curve.
Also for the inverse time overcurrent stage the operating mode is initially set: 2S
PRGH ,S (address ). This stage can be set to operate )RUZDUG (usually
towards line) or 5HYHUVH direction (usually towards busbar) or 1RQ'LUHFWLRQDO
(in both directions). If a particular stage is not required, set its mode to ,QDFWLYH.
it is possible to select from a variety of
0P
Functions
–stage can
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