6–42
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
S3 PROTECTION
CHAPTER 6: SETPOINTS
loading). In such cases, one should check whether or not this setting complies with the
above recommendation regarding the CT linear performance. This breakpoint marks the
end of slope 1, where no CT saturation is expected to restrain (through) currents smaller
than that breakpoint.
BREAK 2
Range: 1.00 to 10.00xCT in steps of 0.01xCT
Default: 1.5xCT
Breakpoint 2 should be set below the fault current that is most likely to saturate any of
the transformer CTs due to an AC component alone. The setting is expressed in times CT
primary of Winding 1. For example if 10 kA is the maximum AC through fault current
before Winding 2 CT (1000:5) starts to saturate, on a 5 MVA transformer with a ratio of
13.8kV/4.16kV, and a Winding1 CT (500:5) rating, the Breakpoint 2 setting will be
6.02 x CT.
In this example:
SLOPE 2
Range: 50 to 100% in steps of 1
Default: 95%
The Slope 2 setting ensures stability during fault conditions of the type that produce CT
saturation and spurious high differential current. Slope 2 should be set high to cater for
the worst case scenario where one set of CTs saturates, but the other set does not. In
such cases the differential/restraint ratio can go as high as 95% to 98%.
INRUSH INHBT FUNCT
Range: Disabled, 2nd Harm Block
Default: 2nd Harm Block
This setting enables or disables the inrush inhibit function. None of the settings for inrush
inhibit are active when the function is set to “Disabled”.
Figure 6-19: Transformer Inrush inhibiting
Fault current (W2) = 10kA
CT primary (W2) = 1000 A/(1
×
CT)
M(W2) =
(
௪ଶ
)×
்
(
௪ଶ
)
(
௪ଵ
)×
்
(
௪ଵ
)
=
ସ
.
ଵ
× (
ଵ
:
ହ
)
ଵଷ
.
଼
×
ହ
:
ହ
= 0.602
Breakpoint 2 =
௨௧
௨௧
(
ௐଶ
)×
ெ
(
ௐଶ
)
்
௬
(
ௐଶ
)
=
ଵ
×
.
ଶ
ଵ
/(
ଵ
×
்
)
= 6.02
ܥܶ
Summary of Contents for 345
Page 89: ...CHAPTER 3 INTERFACES SOFTWARE SETUP 345 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL 3 35 ...
Page 92: ...3 38 345 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL SOFTWARE SETUP CHAPTER 3 INTERFACES ...
Page 254: ...A 8 345 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL CHANGE NOTES ...
