Siemens siprotec SJ62, User Manual

Page: 213 / 715

2 Functions
211
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
Logarithmic
Inverse
characteristic with
Knee Point (inverse
time) The logarithmic inverse characteristic with knee point (see figure 2-76) is set by means
of the parameters
3119 51Ns PICKUP
,
3127 51Ns I T min
,
3128 51Ns I T
knee
,
3132 51Ns TD
,
3140 51Ns T min
and
3141 51Ns T max
.
51Ns T min
and
51Ns T max
define the range of the tripping time where
51Ns T max
is assigned
to the current threshold
51Ns PICKUP
and
51Ns T min
to the current threshold
51Ns I T min
. The knee-point time
51Ns T knee
specifies the tripping time in the
transition point of two characteristic segments with different slope. The transition point
is defined by the current threshold
51Ns I T knee
.
51Ns PICKUP
is the minimum
pickup threshold for the ground-fault pickup current of the overcurrent element. The
tripping time will assume a constant value after reaching a maximum secondary
current of 1.4 A at the latest. The parameter
51Ns TD
serves as time multiplier for the
tripping time.
Figure 2-76 Trip-time characteristics of the inverse-time ground fault protection 51Ns with
logarithmic inverse characteristic with knee point (example for 51Ns = 0.004 A)
User Defined
characteristics (In-
verse Time) If a user-defined characteristic is configured at address
131
,
Sens. Gnd Fault
User Defined PU
, it should be noted that there is a safety factor of 1.1 between
pickup and setting value - as is standard for inverse curves. This means that pickup
will only be initiated when current of 1.1 times the setting value flows.
Entry of the value pair (current and time) is a multiple of the settings at addresses
3119 51Ns PICKUP
and
3120 51NsTIME DIAL
. Therefore, it is recommended that
these addresses are initially set to 1.00 for simplicity. Once the curve is entered, the
settings at addresses
3119
and/or
3120
may be modified if necessary.
The default setting of current values is
∞
. They are, therefore, not enabled — and no
pickup or tripping of these protective functions will occur.
Up to 20 pairs of values (current and time) may be entered at address
3131 M.of
PU TD
. The device then approximates the characteristic, using linear interpolation.