4–118
889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION
CHAPTER 4: SETPOINTS
Figure 4-38: Saturation detection state machine
Phase comparison principle:
The test for direction can be summarized by the following equation:
If
(|I
ts
| > B
1
or
(|I
ts
| > K x I
r
and |I
ts
| > PKP))
and
(|I
ns
| > B
1
or
(|I
ns
| > K x I
r
and
|I
ns
| > PKP))
Then
DIR = abs ( <Its - <Ins ) > 90°
else
DIR = 1
where:
I
r
= restraining current
DIR = flag indicating that the phase comparison principle is satisfied,
B
1
= breakpoint 1 setting,
I
ts
, I
ns
= current phasor at the terminal and neutral side banks, respectively
K = factory constant of 0.25
There are three DIR flags (one per phase). The corresponding FlexLogic operands are:
•
Percent Diff Dir A
•
Percent Diff Dir B
•
Percent Diff Dir C
NOTE
NOTE:
That the above CT saturation (SAT) and phase direction (DIR) checking are applicable to
internal summation method only. If the Core balance method is selected, neither SAT nor
DIR check is performed, the fixed values SAT=0 and DIR = 1 are used.
