12 SIPROTEC 7SJ81/7SK81 V4.70, Product Information
E50417-K1150-C462-A2, Edition 02.2012
Due to the use of low-power current transformers, no physical current sum
can be formed. Therefore the Holmgreen connection and with it the fast
current sum monitoring or for example, the high-impedance ground-fault
differential protection is not possible.
Ratio of the Low-Power Current Transformers
The 7SJ81/7SK81 is equipped with 4 current measuring inputs for low-
power current transformers. The parameters 311 Iph-LPCT PRIM and
314 Uph-LPCT SEC allow you to set the transformation ratio of the low-
power current transformers for the 3 phases of the device.
With the parameters 313 Ignd-LPCT PRIM and 315 Ugnd-LPCT SEC,
you can set the transformation ratio of an optional low-power current
transformer for the ground current input.
An LPCT with a secondary voltage U-LPCT SEC higher than 1000 mV can
be parameterized by applying a linear transformation to the conversion
ratio.
Example: For split core LPCT with a conversion ratio 60 A : 7000 mV, the
parameters can be set as follows:
313 Ignd-LPCT PRIM = 6 A
315 Ugnd-LPCT SEC = 700 mV
Package Function 7SJ81 7SK81
Additional
functionality
67 Directional overcurrent protection phase 67-1,
67-2, 67-3
X
67N Directional overcurrent protection ground
67N-1, 67N-2, 67N-3
XX
67N(s)1 Directional sensitive ground fault protec-
tion 67N(s)-1, 67N(s)-2, 67N(s)-3
XX
59N Displacement voltage XX
27/59 Under/Overvoltage XX
81 U/O Under/Overfrequency, f<, f> XX
47 Phase rotation XX
32/55/81R Flexible protection functions (current
and voltage parameters), Protective function for
voltage, power, power factor, frequency change
XX
Additional
functions
Automatic Reclosing (AR) X
Fault Locator (FL) X
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