Rockwell Automation 865 Differential Protection Relay - Manual (Page 78)

3-34 Protection
Functions
865-UM001A-EN-P – July 2009
Inverse Time Setting Error Signal
If there are any errors in the inverse delay configuration the
appropriate protection stage will use definite time delay.
There is a signal ‘Setting Error’ available in output matrix, which
indicates three different situations:
1.
Settings are currently changed with SetPointPS or local panel,
and there is temporarily an illegal combination of
curve/delay/points. For example if previous settings were
IEC/NI and then curve family is changed to IEEE, the setting
error will active, because there is no NI type available for IEEE
curves. After changing valid delay type for IEEE mode (for
example MI), the ‘Setting Error’ signal will release.
There are errors in formula parameters A…E, and the device
is not able to build the delay curve
There are errors in the programmable curve configuration
and the device is not able to interpolate values between the
given points.
Limitation
The maximum measured phase current is 50xI N and the maximum
directly measured earth fault current is 5xI
0N
. This limits the scope of
inverse curves when the setting is more than 2.5xI
N
(overcurrent
stages and earth fault stages using I
0Calc
input) or 0.25xI
01N
(earth
fault stages using I
01
input or I
02
input). The I
N
and I
01N
and I
02N
depend on the order code (See Chapter 12). The table below gives the
limit values in secondary amperes.
Example of limitation:
CT = 750/5
I
N
= 577 A
CT
0
= 100/1 (a cable CT for I
0
)
Secondary scaled I
GNsec
is now 3.85A
For overcurrent stage I> the table below gives 12.5 A. Thus the
maximum setting for I> stage giving full inverse delay range is 12.5
A / 3.85 A = 3.25 xI
GN
.
For earth fault stage I
0
> and input I
01
the table below gives 0.25 A.
Thus the maximum setting for I
0
> stage giving full inverse delay
range is 0.25A / 1 A = 0.25 pu. This equals a 25A primary earth fault
current.
When using input signal I
0Calc
the corresponding setting is 12.5A / 1 A
= 12.5 pu. This equals a 9375A of primary earth fault current.