Sel SEL-787 - Figure 4.6 Differential Current Alarm Logic Diagram

4.11
Date Code 20150130 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Basic Protection
Selecting Y for E87 enables differential element settings.
When a value is entered in the MVA setting (i.e., MVA is not set to “OFF”),
the relay uses the MVA, winding voltage, CT ratio, and CT connection
settings (seeTable 4.2) you have entered and automatically calculates the
TAP1 and TAP2 values. You can also directly enter tap values when
MVA := OFF. The ratio of maximum (TAPn/INOMn) to the minimum
(TAPn/INOMn) must be less than or equal to 7.5, where INOMn (n = 1, 2) is
the nominal rating of the CT, 5 A or 1 A.
Set the operating current level O87P at a minimum for increased sensitivity
(0.2 to 0.3 for transformers and around 1.0 for buses), but high enough to
avoid operation because of unmonitored loads and transformer excitation
current. O87P must be greater than or equal to the minimum of
0.1 • INOMn/TAPn, where n =1, 2.
The SEL-787 includes a differential current alarm feature. Set the 87AP level
above the highest expected differential current under normal operations
(typically lower than O87P) setting) and a security delay 87AD. See
Figure 4.6 for the logic diagram of this feature. Assertion of Relay Word bit
87AT indicates a problem in the differential current circuit (e.g., open CT).
You must program the 87AT bit to take appropriate action (alarm, display
message, SER, etc.) as desired.
Figure 4.6 Differential Current Alarm Logic Diagram
WDG2 CURR TAP 0.50–31.00 A
a
TAP2 := 2.09
OPERATE CURR LVL 0.10–1.00 TAP O87P := 0.30
DIFF CURR AL LVL OFF, 0.05–1.00 TAP 87AP := 0.15
DIFF CURR AL DLY 1.0–120.0 sec 87AD := 5.0
RESTRAINT SLOPE1 5–90 % SLP1 := 25
RESTRAINT SLOPE2 5–90 % SLP2 := 70
RES SLOPE1 LIMIT 1.0–20.0 TAP IRS1 := 6.0
UNRES CURR LVL 1.0–20.0 TAP U87P := 10.0
2ND HARM BLOCK OFF, 5–100 % PCT2 := 15
4TH HARM BLOCK OFF, 5–100 % PCT4 := 15
5TH HARM BLOCK OFF, 5–100 % PCT5 := 35
5TH HARM AL LVL OFF, 0.02–3.20 TAP TH5P := OFF
5TH HARM AL DLY 0.0–120.0 sec TH5D := 1.0
HARMONIC RESTRNT Y, N HRSTR := Y
HARMONIC BLOCK Y, N HBLK := N
a
Range shown for I
NOM
=5 A; Range for I
NOM
= 1 A is 0.10–6.20 A.
Table 4.4 Differential Element Settings (Sheet 2 of 2)
Setting Prompt Setting Range
Setting Name :=
Fac tory Defau lt
87AP
(setting)
87AD
0
IOP1
_
+
87AT
87AP
AP2
AP3
AP1
Relay
Word
Bits