Siemens SIPROTEC 7ST6 Manual page 80

2 Functions
With the parameter I>> (address 2608) the pickup threshold of the high-set current
High-set Current
Stage I>> stage is specified.
When using a personal computer and DIGSI
tionally entered as primary or secondary values. If secondary quantities are used, all
currents must be converted to the secondary side of the current transformers.
The delay time of the very high set current stage T I>> is set in address 2609.
The delay set is in addition to the pickup time which does not include the operating
time (measuring time).
The dropout to pickup ratio of the stage is 0.95.
Overcurrent Stage If the overcurrent stage is to be operated as a definite-time overcurrent protection,
address 2602 CURVE O/C must be set to Definite Time.
I> in Definite-time
Overcurrent Pro-
For the setting of the current pickup value, I> (address 2614), the maximum operat-
tection
ing current is most decisive. Pickup due to overload should never occur, since the
device in this operating mode operates as fault protection with correspondingly short
tripping times and not as overload protection. Therefore, the pickup value is set to
about 20 % above the maximum expected overload.
When using a personal computer and DIGSI
tionally entered as primary or secondary values. If secondary quantities are used, all
currents must be converted to the secondary side of the current transformers.
The time delay T I> (address 2615) results from the time grading schedule designed
for the network. If implemented as emergency overcurrent protection, shorter tripping
times are advisable (one grading time step above the fast tripping stage), as this func-
tion is only activated in the case of the loss of the local measured voltage.
The delay set is in addition to the pickup time which does not include the operating
time (measuring time).
The dropout to pickup ratio of the stage is 0.95.
Overcurrent Stage If the overcurrent stage is to be operated as an inverse-time stage with IEC character-
istics, address 2602 CURVE O/C must be set to TOC IEC.
IP in Inverse-time
Overcurrent Pro-
With IEC characteristics, the following characteristics are available in address 2611
tection with IEC
IEC Curve:
Characteristics
Normal Inverse (inverse, type A according to IEC 60255-3),
Very Inverse (very inverse, type B according to IEC 60255-3),
Extremely Inv. (extremely inverse, type C according to IEC 60255-3), and
LongTimeInverse (longtime, type B according to IEC 60255-3).
For the setting of the pickup value IP (address 2617), the following must be observed:
Pickup only occurs at a current which is approximately 10 % above the set value. The
dropout threshold is the setting value.
The time multiplier T IP (address 2618) derives from the time grading schedule set
for the network.
80
®
to apply the settings, these can be op-
®
to apply the settings, these can be op-
E50417-G1176-C251-A3
7ST6 Manual