ABB RED615 Technical Manual page 668

Section 8
Measurement functions
662
Tap position decoder
When there is a wired connection to the TAP_POS connector, the corresponding
tap changer position is decoded from the mA or RTD input. When there is no wired
connection to the TAP_POS connector, the binary inputs are expected to be used
for the tap changer position information. The tap changer position value and
quality are internally shared to other functions. The value is available through the
Monitored data view.
The function has three alternative user selectable operation modes: "NAT2INT",
"BCD2INT" and "GRAY2INT". The operation mode is selected with the
Operation mode setting. Each operation mode can be used to convert a maximum
of 6–bit coded input to an 8–bit signed short integer output. For less than 6–bit
input, for example 19 positions with 5 bits when the BCD coding is used, the rest
of the bits can be set to FALSE (0).
The operation mode "NAT2INT" is selected when the natural binary coding is used
for showing the position of the transformer tap changer. The basic principle of the
natural binary coding is to calculate the sum of the bits set to TRUE (1). The LSB
has the factor 1. Each following bit has the previous factor multiplied by 2. This is
also called dual coding.
The operation mode "BCD2INT" is selected when the binary-coded decimal
coding is used for showing the position of the transformer tap changer. The basic
principle 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.
1YHT530004D05 D
615 series
Technical Manual