Siemens siprotec 7SJ63 - Page 180

Functions
6-16 7SJ63 Manual
C53000-G1140-C120-1
The reactance value is entered as a secondary value at address  in ohms per
mile if address  is set to Miles, or at address  in ohms per kilometer if ad-
dress  is set to Kilometers (see Subsection 6.1.1 under “Units of Length”). If the
setting of address  is modified after entry of a reactance value at address 
or , the reactance value must be modified and reentered accordingly.
The calculation of primary ohms in terms of secondary ohms is accomplished using
the following formula:
Because the reactance value must be entered in secondary ohms per unit length, the
formula above must be used to convert primary ohms per unit length into secondary
ohms per unit length as shown below:
Example calculation:
The same example used to illustrate calculation of ground impedance ratios will be
used to illustrate calculation of the reactance setting, with the following additional data
on the current transformers and voltage transformers:
Current transformer 500 A / 5 A
Voltage transformer 20 kV / 0.1 kV
The secondary reactance value is calculated as follows:
This value is entered at Address .
Recognition of
Running Condition
(only for motors)
Address  ,0272567$57, is used for motor protection applications and corre-
sponds to the minimum starting current of the protected motor. The current setting en-
tered at address  enables the device to determine if the protected motor is in
start-up mode, thus allowing the device to properly perform the start-up time monitor-
ing and overload protection functions.
In determining the setting for address , the following should be considered:
• A setting must be selected that is lower than the actual motor start-up current under
all load and voltage conditions.
Z
ondarysec
Current-Transformer-Ratio
Voltage-Transformer - Ratio
--------------------------------------------------------------------------
Z
primary
⋅
=
X’
sec
N
CTR
N
VTR
--------------
X’
prim
⋅
=
where:
N
CTR
= Current transformer ratio
N
VTR
= Voltage transformer ratio
X’
sec
N
CTR
N
VTR
---------------
X’
prim
⋅
500 A/5 A
20 kV/0.1 kV
-----------------------------------
0.55 Ω/mile⋅ 0.275 Ω/mile== =
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