ABB RELION 620 Series Technical Manual page 981

1MRS757644 F
620 series
Technical Manual
GUID-D3B3C7DB-1E8C-4189-9554-77C8B5ACD17D V1 EN
Figure 502: Functional module diagram
Tap position decoder
When there is a wired connection to the TAP_POS input 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 in the Monitored data view
or as a TAP_POS output signal.
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.
Section 8
Measurement functions
975