Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

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4.137
Date Code 20170814 Instruction Manual SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
Convert Maximum Loads to Equivalent Secondary Impedances.
Start
with maximum forward load:
Now, calculate the equivalent secondary impedance:
This secondary value can be calculated more expediently with the following
equation:
Again, for the maximum forward load:
To provide a margin for setting ZLF, multiply by a factor of 0.9:
For the maximum reverse load:
Again, to provide a margin for setting ZLR:
Convert Power Factors to Equivalent Load Angles.
The power factor
(forward load) can vary from 0.90 lag to 0.95 lead.
Setting PLAF := cos
–
1
(0.90) = 26°
Setting NLAF := cos
–
1
(0.95) =
–
18°
The power factor (reverse load) can vary from 0.80 lag to 0.95 lead.
Setting PLAR := 180
°
–
cos
–
1
(0.95) = 180
°
–
18
°
= 162
°
Setting NLAR := 180
°
+ cos
–
1
(0.80) = 180
°
+ 37
°
= 217
°
800 MVA • (1/3) 267 MVA per phase
230 kV • (1/

3) = 132.8 kV line-to-neutral
267 MVA • (1/132.8 kV) • (1000kV/MV) = 2010 A primary
2010 A primary • (1/CT ratio) = 2010 A primary •
(1 A secondary/400 A
primary)
= 5.03 A secondary
132.8 kV • (1000 V/kV) = 132800 V primary
132800 V primary • (1/PT ratio) = 132800 V primary •
(1 V secondary/2000 V
primary)
= 66.4 V secondary
66.4 V secondary
5.03 A secondary
------------------------------------------ 13.2

secondary =
line-line voltage in kV
 
2
CT ratio •
3-phase load in MVA PT ratio •
----------------------------------------------------------------------------------------
230
2
400 •
800 2000 •
--------------------------- 13.2

secondary =
ZLF 13.2

secondary 0.9 • =
11.90

secondary =
230
2
400 •
500 2000 •
--------------------------- 21.1

secondary =
ZLR 21.1 secondary 0.9 • =
19.00

secondary =