Sel 551 - Settings Sheets

4.20
SEL-551 Relay Instruction Manual Date Code 20110408
Setting the Relay
Settings Sheets
Equation 4.5
Example 3: Determine Whether the Following Application Meets the
Above Criteria
Apply Equation 4.1 to verify if the CTs meet the required criteria.
Equation 4.6
The calculation shows that the 400:5 (class C400) CT meets the criteria in
Equation 4.1.
Other System
Parameters
The relay settings NFREQ and PHROT allow you to configure the SEL-551 to
your specific system.
➤ Set NFREQ equal to your nominal power system frequency,
either 50 Hz or 60 Hz.
➤ Set PHROT equal to your power system phase rotation, either
ABC or ACB.
Set DATE_F to format the date displayed in relay reports and the front-panel
display.
➤ Set DATE_F to MDY to display dates in Month/Day/Year
format.
➤ Set DATE_F to YMD to display dates in Year/Month/Day
format.
Settings Sheets
The settings sheets that follow include the definition and input range for each
setting in the relay. Refer to Overcurrent Elements on page 1.6 for information
on 5 A nominal and 1 A nominal ordering options and how they influence
overcurrent element setting ranges.
CT
RATING
1
X
R
----+
⎝⎠
⎛⎞
262.5
-------------------
100
ANSI
---------------
I
MAX
Z
B
• • • =
120+()
262.5
--------------------
100
400
---------
40000 0.50• • • =
400 A=
Description Value
CTs used 400:5 A, class C400
Instantaneous element pickup setting 80 A secondary
Maximum current for a line-to-line fault 40000 Α primary
X/R ratio 20
Total CT secondary burden 0.50 ohm
X
R
----1+
⎝⎠
⎛⎞
I
f
Z
b
• • 20 1+()
40000
400
---------------
0.50Ω
4
--------------
• • =
262.5=