Figure 512: 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.
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.
1MRS757644 H
Measurement functions
620 series
Technical Manual
977