NOTE
Unmonitored capacitor banks should be avoided if possible. Or, they must be treated
very carefully to avoid false tripping due to inrush currents.
S
Calculate desired minimum pickup
tep 1.
setting in times tap. Choose the desired minimum pickup in
per unit on the transformer full load base (0.25). Multiply this times the factor X calculated using
the following equation. If the ideal tap (TAPn
I
) is equal to the actual tap (TAPn
A
), the factor will be
1. For this example, this is the case, so the minimum pickup of 0.25 per unit will equal a
minimum pickup of 0.25 times tap.
D-16
BE1-CDS240 Settings Calculations
9365200990 Rev F
CTRn
KVn
TAPn
TAPn
X
A
A
I
*
*
3
*
COMPn
MVA
TAPn
*
1000
*
Step 2. Calculate the unmonitored load in times tap. Use the following equation:
CTRn
TAPn
Iunmon
*
COMPn
pri
Iunmon
*
0
Iunmon
Step 3. Calculate the Minpu setting. Add the two to get the minpu setting.
tep 4. Convert pickup setting to primary amperes.
As a reality check, convert the minimum sensitivity to high side and low side primary amperes. The
ickup settings in times tap can be rela d to primary amperes by this equation:
Minpu
= 0.25 + 0
= 0.25
S
p
te
Ipri
Mpu TAPn CTRn
COMPn
*
*
41
1
60
*
79
.
2
*
25
.
0
Ipri
amperes @ 69 kV
231
1
160
*
79
.
5
*
25
.
0
Ipri
amperes @ 12.47 kV
nd
ntal component of the operate current for use by
inrush with a sensitive setting.
Choose Unrestrained Pickup Setting
This two-step process selects the unrestraint element setting to provide security for both inrush and
external fault conditions.
Step 1. Calculate the expected inrush current based upon the self-cooled rating of the transformer.
Asymmetrical CT saturation during a heavy internal fault generates 2 harmonics that can inhibit the
sensitive percentage restrained unit until the CT recovers. The unrestrained unit provides fast clearing for
these internal faults. Thus, the unrestrained unit should be set as sensitively as possible without
operating on inrush.
Typical numbers used in the industry for inrush have been eight to twelve times the rating of the
transformer. Due to the operating characteristics of the BE1-CDS240 unrestrained differential element, a
setting of six times the self-cooled rating provides security for inrush. We can use a lower URO pickup
setting and maintain security for unrestrained tripping because inrush current typically has a high peak
that is non-sinusoidal. The relay extracts the fundame
the unrestrained element to greatly reduce its sensitivity to this non-sinusoidal inrush current. In addition,
the high initial peak generally decays quickly to a lower value. The slight inverseness of the unrestraint
tripping characteristic (refer to Section 1,
General Information)
provides additional security from
unrestrained tripping on
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 ...
Page 290: ...9 4 BE1 CDS240 Security 9365200990 Rev F This page intentionally left blank ...
Page 292: ...ii BE1 CDS240 Human Machine Interface 9365200990 Rev F This page intentionally left blank ...
Page 306: ...10 14 BE1 CDS240 Human Machine Interface 9365200990 Rev F This page intentionally left blank ...
Page 308: ...ii BE1 CDS240 ASCII Command Interface 9365200990 Rev F This page intentionally left blank ...
Page 342: ...11 34 BE1 CDS240 ASCII Command Interface 9365200990 Rev F This page intentionally left blank ...
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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Page 468: ...13 92 BE1 CDS240 Testing and Maintenance 9365200990 Rev F This page intentionally left blank ...
Page 512: ...14 42 BE1 CDS240 BESTCOMS Software 9365200990 Rev F This page intentionally left blank ...
Page 544: ...ii BE1 CDS240 Terminal Communication 9365200990 Rev F This page intentionally left blank ...
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