Applying The Function Parameter Settings - Siemens siprotec 7SA6 User Manual

Functions
6.9.2

Applying the Function Parameter Settings

General
High Set
Overcurrent Stages
Iph>>, 3I0>>
6-148
During the configuration of the device scope of functions (refer to Section 5.1, address
) it was determined which characteristics are to be available. Only those
parameters that apply to the available characteristics, according to the selected
configuration and the version of the device, are accessible in the procedures
described below.
According to the desired operating mode of the overcurrent protection the address
 is set: 2SHUDWLQJ 0RGH = 21 means that the overcurrent protection operates
independent on the other protection functions, in other words, as back-up overcurrent
protection. If the overcurrent protection should only operate as emergency protection
during loss of VT–supply, the setting 2QO\ E\ 97 ORVV must be applied. Finally, the
overcurrent protection can also be switched 2)).
If not all the stages are required, the time delay of those stages that are not used can
be deactivated by setting the pickup value to ∞. But if you set an associated time delay
to ∞ this does not suppress the pick-up annunciations, but merely prevents the time
delay from expiring.
The stub protection remains in service even if the overcurrent mode of operation
setting is 2QO\ E\ 97 ORVV.
One or more stages can be set as fast tripping stages when switching on to a dead
fault. This will be determined when setting the individual stages (see below). To avoid
a spurious pick-up due to transient overcurrents, the delay 7 627) (address )
can be set. Typically the presetting of 0 is correct. On long cables, where large inrush
currents may arise, or on transformers, a short time delay setting may be reasonable.
The time delay depends on the severity and duration of the transient overcurrents as
well as on which stages were selected for the fast switch onto fault clearance.
The I>>–stages ,SK!! (address ) and ,!! (address ) along with the
I>–stages or the I –stages result in a dual stage characteristic. Of course, it is also
p
possible to combine all three stages. If a particular stage is not required, its pickup
value is set to ∞. The I>>–stages always operate with a defined time delay.
If the I>>–stages are used as a fast tripping stage prior to automatic reclosure, the
current setting corresponds to that of the I>– or I
only the difference in the trip delay times is of interest. The times 7 ,SK!! (address
) and 7 ,!! (address ) can be set to  or a very small value as rapid
clearance of the fault current prior to an automatic reclosure has preference above the
selective fault clearance. Prior to the final trip, these stages must be blocked to
achieve selective final clearance of the fault.
On very long lines with a small source impedance or in front of large reactances (e.g.
transformers, series reactors), the I>>–stages can also be used for current grading. In
this case they must be set such that they definitely do not pick up for a fault at the end
of the line. The time delays can then be set to  or a very small value.
When using a personal computer and DIGSI
optionally entered as primary or secondary values. When applying the setting
parameters as secondary values, the primary currents must be converted to the
secondary side of the current transformer.
Calculation example:
110 kV overhead line 150 mm
–stages (see below). In this case
p
®
4 to apply the settings, these can be
2
as used in the example in Subsubsection 6.2.4.2:
7SA6 Manual
C53000-G1176-C133-1