ABB RELION REX640 Technical Manual page 1500

Measurement functions
with the binary-coded decimal coding is to calculate the sum of the bits set to TRUE
(1). The four bits nibble (BI3...BI0) have a typical factor to the natural binary coding.
The sum of the values should not be more than 9. If the nibble sum is greater than 9,
the tap position output validity is regarded as bad.
The operation mode "GRAY2INT" is selected when the binary-reflected Gray coding
is used for showing the position of the transformer tap changer. The basic principle
of the Gray coding is that only one actual bit changes value with consecutive
positions. This function is based on the common binary-reflected Gray code which
is used with some tap changers. Changing the bit closest to the right side bit gives
a new pattern.
An additional separate input, SIGN_BIT, can be used for negative values. If the
values are positive, the input is set to FALSE (0). If the SIGN_BIT is set to TRUE (1)
making the number negative, the remaining bits are identical to those of the coded
positive number.
The tap position validity is set to good in all valid cases. The quality is set to bad in
invalid combinations in the binary inputs. For example, when the "BCD2INT" mode
is selected and the input binary combination is "0001101", the quality is set to bad.
For negative values, when the SIGN_BIT is set to TRUE (1) and the input binary
combination is "1011011", the quality is set to bad.
If the tap changer has auxiliary contacts for indicating the extreme positions of the
tap changer, their status can be connected to END_POS_R and END_POS_L inputs.
The END_POS_R (End position raise or highest allowed tap position reached) status
refers to the extreme position that results in the highest number of the taps in
the tap changer. Similarly, END_POS_L (End position lower or lowest allowed tap
position reached) status refers to the extreme position that results in the lowest
number of the taps in the tap changer. TAP_POS output is dedicated for transferring
the validated tap position for the functions that need tap position information, for
example OL5ATCC and TRxPTDF. It includes both the actual position information
and the status of reached end positions, assuming that inputs END_POS_R and
END_POS_L are connected.
Table 1449: Truth table of the decoding modes
Inputs
SIGN_
BIT
...
1
1
1
0
0
0
0
0
0
0
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1500
BI5 BI4 BI3
...
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
BI2 BI1 BI0
... ...
0 1 1
0 1 0
0 0 1
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1MRS759142 F
TAP_POS outputs
NAT2I BCD2I GRAY2
NT NT INT
... ... ...
-3 -3 -2
-2 -2 -3
-1 -1 -1
0 0 0
1 1 1
2 2 3
3 3 2
4 4 7
5 5 6
6 6 4
REX640
Technical Manual