9.39
Date Code 20070117
Instruction Manual
SEL-351-5, -6, -7 Relay
Setting the Relay
Settings Explanations
Example 2: Minimum CT Rating With an 80 A Instantaneous Setting
CT rating in terms of maximum fault current, X/R ratio, ANSI rating, and
burden is:
Equation 9.3
With an 80 amp instantaneous setting, what is the minimum CT rating that can
be used when the maximum fault current is 40000 amps, X/R = 20, and the
burden is 0.50
Ω
ohms.
Example 3: Determine Whether the Following Application Meets the
Above Criteria
Apply
to verify if the CTs meet the required criteria.
The calculation shows that the 400:5 (class C400) CT meets the criteria in
.
Settings for Voltage
Input Configuration
SEL-351-5, -6, -7 relays with firmware version R308 or lower can only accept
wye-connected PTs to the voltage inputs, and can only use voltage input
VS
as
a synchronism check voltage/auxiliary voltage input. Beginning with
firmware revision R309, these relays have two new global settings, PTCONN
and VSCONN; and group setting VNOM accepts a value of OFF.
Voltage Input Configuration (See Settings for Voltage Input
Configuration on page 9.39) on page SET.24
.
I
MAX
262.5
1
X
R
----
+
⎝
⎠
⎛
⎞
-------------------
ANSI
100
Z
B
•
----------------------
CT
RATING
• •
=
262.5
1
20
+
(
)
--------------------
400
100
0.50
Ω
•
-------------------------------
400 40000
A
=
• •
=
CT
RATING
1
X
R
----
+
⎝
⎠
⎛
⎞
262.5
-------------------
100
ANSI
---------------
I
MAX
Z
B
• • •
=
CT
RATING
1
X
R
----
+
⎝
⎠
⎛
⎞
262.5
-------------------
100
ANSI
---------------
I
MAX
Z
B
• • •
=
1
20
+
(
)
262.5
--------------------
100
400
---------
40000
0.50
• 400
A
=
• •
=
CTs used
400:5 A, class C400
Instantaneous element pickup setting
80 A secondary
Maximum current for a line-to-line fault
40000 A primary
X/R ratio
20
Total CT secondary burden
0.50
Ω
ohm
X
R
----
1
+
⎝
⎠
⎛
⎞
I
f
Z
b
• •
20
1
+
(
)
40000
400
---------------
0.50
Ω
4
---------------
262.5
=
• •
=
Summary of Contents for SEL-351-5
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