Siemens siprotec SJ62, User Manual

Page: 82 / 715

2.2 Overcurrent Protection 50, 51, 50N, 51N
80
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
When using DIGSI to modify settings, a dialog box is available to enter up to 20 value
pairs for a characteristic curve (see figure 2-14).
In order to represent the characteristic graphically, the user should click on
"characteristic". The previously entered characteristic will appear as shown in Figure
2-14.
The characteristic curve shown in the graph can be modified later on. Placing the
mouse cursor over a point on the characteristic, the cursor changes to the shape of a
hand. Press and hold the left mouse button and drag the data item to the desired po-
sition. Releasing the mouse button will automatically update the value in the value
table.
The respective upper limits for the value setting range are indicated by dotted lines in
the right-hand and upper area of the system of coordinates. If the position of a data
point lies outside these limits, the associated value will be set to infinity.
Figure 2-14 Inputting and visualizing a user-defined trip curve with DIGSI – Example
Inrush Restraint When applying the protection device to transformers where high inrush currents are
to be expected, the 7SJ62/63/64 can make use of an inrush restraint function for the
overcurrent elements 50–1, 51, 50N–1 and 51N as well as the non-directional over-
current elements.
Inrush restraint is only effective and accessible if address
122 InrushRestraint
was set to
Enabled
during configuration. If the function is not required
Disabled
is
to be set. In address
2201 INRUSH REST.
the function is switched
ON
or
OFF
jointly
for the overcurrent elements 50–1, 51, 50N-1 and 51N.
The inrush restraint is based on the evaluation of the 2nd harmonic present in the
inrush current. Upon delivery from the factory, a ratio
I
2f
/ I
f
of 15 % is set. Under normal
circumstances, this setting will not need to be changed. The setting value is identical
for all phases and ground. However, the component required for restraint may be ad-
justed to system conditions in address
2202 2nd HARMONIC
. To provide more re-
straint in exceptional cases, where energizing conditions are particularly unfavour-
able, a smaller value can be set in the address before-mentioned, e.g. 12 %.
The effective duration of the cross-blocking
2203 CROSS BLK TIMER
can be set to
a value between 0 s (harmonic restraint active for each phase individually) and a
maximum of 180 s (harmonic restraint of a phase also blocks the other phases for the
specified duration).