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 87T. 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 855:
Truth table of the decoding modes
Inputs
TAP_POS outputs
SIGN_
BIT
BI5
BI4
BI3
BI2
BI1
BI0
NAT2I
NT
BCD2I
NT
GRAY2
INT
...
...
...
...
...
...
...
1
0
0
0
0
1
1
-3
-3
-2
1
0
0
0
0
1
0
-2
-2
-3
1
0
0
0
0
0
1
-1
-1
-1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
0
1
0
2
2
3
0
0
0
0
0
1
1
3
3
2
0
0
0
0
1
0
0
4
4
7
0
0
0
0
1
0
1
5
5
6
Table continues on next page
Section 8
1MAC059074-MB A
Measurement functions
952
615 series ANSI
Technical Manual
Summary of Contents for Relion 615 series
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