Siemens siprotec 7SD5 User Manual page 222

2 Functions
Moderately Inv.,
Very Inverse,
Extremely Inv.,
Definite Inv..
The characteristics and equations they are based on are listed in the Technical Data.
The setting of the pickup threshold 3I0p PICKUP (address 3141) is similar to the
setting of definite time stages (see above). In this case it must be noted that a safety
margin between the pickup threshold and the set value has already been incorporat-
ed. Pickup only occurs at a current which is approximately 10 % above the set value.
The time multiplier setting 3I0p Time Dial (address 3144) is derived from the
grading coordination chart which was set up for earth faults in the system.
In addition to the inverse time delay, a constant (fixed length) time delay can also be
set if this is required. The setting Add.T-DELAY (address 3147) is added to the time
of the set curve.
During the selection of the current and time settings, regard must be taken as to
whether a stage should be direction dependent and whether it uses teleprotection.
Refer also to the margin headings „Determination of Direction" and „Teleprotection
with Earth Fault Protection".
Inverse Time Stage If you have configured the inverse time overcurrent stage with the logarithmic inverse
characteristic (address 131 Earth Fault O/C = TOC Logarithm.), the operating
with Logarithmic
mode is initially set: address 3140 Op. mode 3I0p. The stage can be set to operate
Inverse Character-
Forward (usually towards line), Reverse (usually towards busbar) or Non-
istic
Directional (in both directions). If the stage is not required, set its mode to
Inactive.
For the logarithmic inverse characteristic (address 131 Earth Fault O/C = TOC
Logarithm.) the setting of address is 3153 ANSI Curve = Log. inverse.
The characteristics and equations they are based on are listed in the Technical Data.
Figure 2-97 illustrates the influence of the most important setting parameters on the
curve. 3I0p PICKUP (address 3141) is the reference value for all current values,
while 3I0p Startpoint (address 3154) determines the beginning of the curve, i.e.
the lowest operating range on the current axis (referred to 3I0p PICKUP). The timer
setting 3I0p MaxT-DELAY (address 3146) determines the starting point of the curve
(for 3I
the slope of the curve. For large currents, 3I0p MinT-DELAY (address 3142) deter-
mines the lower limit on the time axis. For currents larger than 30 · 3I0p PICKUP the
operating time no longer decreases.
Finally in address 3147 Add.T-DELAY a fixed time delay can be set as was done for
other curves.
During the selection of the current and time settings, regard must be taken as to
whether a stage should be direction dependent and whether it uses teleprotection.
Refer also to the margin headings „Determination of Direction" and „Teleprotection
with Earth Fault Protection".
222
= 3I0p PICKUP). The time factor 3I0p Time Dial (address 3145) changes
0
7SD5 Manual
C53000-G1176-C169-1