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 :=
Facto ry 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.
50Pn1P := OFF
50Pn1P := OFF
PHASE IOC DELAY 0.00–5.00 sec 50Pn1D := 0.00
PH IOC TRQCTRL SEL
OGIC 50Pn1TC := 1
PHASE IOC LEVEL OFF, 0.50–96.00 A
a
,
0.10–19.20 A
b
50Pn2P := OFF
50Pn2P := OFF
PHASE IOC DELAY 0.00–5.00 sec 50Pn2D := 0.00
PH IOC TRQCTRL SEL
OGIC 50Pn2TC := 1
PHASE IOC LEVEL OFF, 0.50–96.00 A
a
,
0.10–19.20 A
b
50Pn3P := OFF
50Pn3P := OFF
PHASE IOC DELAY 0.00–5.00 sec 50Pn3D := 0.00
PH IOC TRQCTRL SEL
OGIC 50Pn3TC := 1
PHASE IOC LEVEL OFF, 0.50–96.00 A
a
,
0.10–19.20 A
b
50Pn4P := OFF
50Pn4P := OFF
PHASE IOC DELAY 0.00–5.00 sec 50Pn4D := 0.00
PH IOC TRQCTRL SEL
OGIC 50Pn4TC := 1
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