where
V
e
is the internal excitation voltage (
R
CT
* I
F
) at the maximum fault current
I
F
and
V10`
is the
voltage of the curve passing through point Q where the exciting is 10 amps. This voltage is practically
in
Figure D-6, for instance), the saturation factor defined on the excitation curve appears to be lower, i.e.,
o compare the two saturation factor definitions.
D-7 and the ANSI Accuracy Class definition that the CT must be
, we now develop a comparative
analysis between the two definitions:
o compare the two expressions, we
ultaneous variations of the parameters. The following example is based on a C200 (
Zc
=2)
with
R
s
varying from 0.1 to 0.8 ohms and
ZB
varying from 0.1 to 2 times
Z
c
ohms (load angles are
close to the knee-point voltage
VK`
which would yield nearly the same (a slightly more conservative)
result.
Since in all likelihood, the excitation voltage capability of the CT will be higher (passing through point R
more favorable. A detailed analysis can be performed t
Saturation Factor SF vs SF’ Definitions Compared
Using the equivalent circuit in Figure
Zc
able to source 20 times nominal current into a standard burden
9365200990 Rev F
BE1-CDS240 Settings Calculations
D-25
T
take the ratio
SF`/SF:
Since this expression varies with the ratio of the actual relay circuit burden (
ZB
) to the accuracy class
burden (
Zc
) and the CT internal resistance (
Rs
), it is best visualized with a surface plot (Figure D-7)
showing sim
neglected).
Figure D-9. SF`/SF Ratio
The 0 to 20 axis represents the variations x10 of
ZB
(20 is 2x
Zc
). The 0 to 8 axis represents the
variations x10 of
R
CT
in ohms. The vertical axis (0 to 4) shows that for
ZB
values equal to or greater than
the burden value Zc, the two saturation factor equations are nearly identical. The ANSI Accuracy Class
method yields the larger, more conservative result. For low values of
ZB
and large values of
R
CT
, the
Excitation Curve method yields a larger saturation factor. Since the Excitation Curve method is closely
following the CT characteristics, it may be said that the ANSI Class method that neglects the CT internal
VC
SF
VT
`
10
`
V
Ve
SF
Zc
*
100
IF
*
ZB
SF
)
Rs
Zc
(
*
)
Rs
ZB
(
*
IF
`
SF
100
0
2
4
6
8
0
2
4
6
8
10
12
14
16
18
20
0
1
2
)
CT
Zc
(
*
ZB
SF
)
'
CT
ZB
(
Zc
`
SF
3
Summary of Contents for BE1-CDS240
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Page 38: ...1 28 BE1 CDS240 General Information 9365200990 Rev F This page intentionally left blank ...
Page 40: ...ii BE1 CDS240 Quick Start 9365200990 Rev F This page intentionally left blank ...
Page 152: ...ii BE1 CDS240 Metering 9365200990 Rev F This page intentionally left blank ...
Page 226: ...iv BE1 CDS240 Application 9365200990 Rev F This page intentionally left blank ...
Page 286: ...ii BE1 CDS240 Security 9365200990 Rev F This page intentionally left blank ...
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Page 308: ...ii BE1 CDS240 ASCII Command Interface 9365200990 Rev F This page intentionally left blank ...
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Page 349: ...Figure 12 5 Horizontal Rack Mount Front View 9365200990 Rev F BE1 CDS240 Installation 12 5 ...
Page 361: ...Figure 12 17 Typical DC Connection Diagrams 9365200990 Rev F BE1 CDS240 Installation 12 17 ...
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