Schweitzer Engineering Laboratories SEL-787, Instruction Manual, Page: 109 / 564

4.31
Date Code 20081022 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Basic Protection
The REF1POL setting defines which line CTs the relay uses for REF. For
example, if REF1POL = 12, use higher primary rated current of CTR1 or
CTR2 in the above equation.
An example 50REF1P calculation is as follows, assuming that CTRN1 = 40,
INOMN1 = 5 A, MAX (I
NOM
• CTR) = (160 • 5) = 800, and load unbalance is
10 percent:
Criterion 2 minimum setting of 50REF1P is 0.20 pu. With a 10 percent load
unbalance, we can assume the criterion 1 value to be 0.1 pu. Because
50REF1P must be set at the greater of the two criteria values, we would select
a setting of 0.20 pu.
Overcurrent Elements
Four levels of phase, and two levels each of residual and negative sequence,
instantaneous/definite-time overcurrent elements are available for each of the
two transformer windings as shown in
Table 4.6 through Table 4.8 and in
Figure 4.14 .
Each element can be torque controlled using appropriate SEL
OGIC
control
equations (e.g., when 50P11TC := IN401, the 50P11 element will be
operational only if IN401 is asserted).
50REF1P 0.05
800
40 5
•
--------------
• ≥
50REF1P 0.20 pu
≥
Table 4.6 Winding n Maximum Phase Overcurrent Settings (n = 1 or 2)
Setting Prompt Setting Range
Setting Name :=
Factory Default
PHASE IOC LEVEL OFF, 0.50–96.00 A
a
,
0.10–19.20 A
b
a
For I
NOM
= 5 A.
b
For I
NOM
= 1 A.
50P n 1P := OFF
50P n 1P := OFF
PHASE IOC DELAY 0.00–5.00 sec 50P n 1D := 0.00
PH IOC TRQCTRL SEL
OGIC
50P n 1TC := 1
PHASE IOC LEVEL OFF, 0.50–96.00 A
a
,
0.10–19.20 A
b
50P n 2P := OFF
50P n 2P := OFF
PHASE IOC DELAY 0.00–5.00 sec 50P n 2D := 0.00
PH IOC TRQCTRL SEL
OGIC
50P n 2TC := 1
PHASE IOC LEVEL OFF, 0.50–96.00 A
a
,
0.10–19.20 A
b
50P n 3P := OFF
50P n 3P := OFF
PHASE IOC DELAY 0.00–5.00 sec 50P n 3D := 0.00
PH IOC TRQCTRL SEL
OGIC
50P n 3TC := 1
PHASE IOC LEVEL OFF, 0.50–96.00 A
a
,
0.10–19.20 A
b
50P n 4P := OFF
50P n 4P := OFF
PHASE IOC DELAY 0.00–5.00 sec 50P n 4D := 0.00
PH IOC TRQCTRL SEL
OGIC
50P n 4TC := 1