ABB 615 series Technical Manual page 957

1MAC059074-MB A
615 series ANSI
Technical Manual
The operation of 84T can be described using a module diagram. All the modules in the
diagram are explained in the next sections.
GUID-D3B3C7DB-1E8C-4189-9554-77C8B5ACD17D V1 EN
Figure 480: 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.
Section 8
Measurement functions
951