GE Power Management
745 Transformer Management Relay
5-91
5 SETPOINTS
5.9 TIME OVERCURRENT CURVES
5
5.9 TIME OVERCURRENT CURVES
5.9.1 NOTE
Graphs of time-current curves on 11”x17” log-log graph paper are available upon request.
5.9.2 ANSI CURVES
The ANSI time overcurrent curve shapes conform to industry standard curves and fit into the ANSI C37.90
curve classifications for extremely, very, normally, and moderately inverse. The 745 ANSI curves are derived
from the following formula:
where:
T
= Operate Time (seconds)
M
= Multiplier setpoint
I
= Input Current
I
pkp
= Pickup Current setpoint
A
,
B
,
C
,
D
,
E
= Constants
Table 5–10: ANSI CURVE CONSTANTS
ANSI CURVE SHAPE
CONSTANTS
A
B
C
D
E
EXTREMELY INVERSE
0.0399
0.2294
0.5000
3.0094
0.7222
VERY INVERSE
0.0615
0.7989
0.3400
–0.2840
4.0505
NORMALLY INVERSE
0.0274
2.2614
0.3000
–4.1899
9.1272
MODERATELY INVERSE
0.1735
0.6791
0.8000
–0.0800
0.1271
NOTE
T
M
A
B
1.03
C
–
----------------------
D
1.03
C
–
(
)
2
-----------------------------
E
1.03
C
–
(
)
3
-----------------------------
+
+
+
, for 1
I
I
pkp
---------
1.03
<
≤
×
M
A
B
I I
pkp
⁄
C
–
-------------------------
D
I I
pkp
⁄
C
–
(
)
2
---------------------------------
E
I I
pkp
⁄
C
–
(
)
3
---------------------------------
+
+
+
, for 1.03
I
I
pkp
---------
20.0
<
≤
×
M
A
B
20.0
C
–
----------------------
D
20.0
C
–
(
)
2
-----------------------------
E
20.0
C
–
(
)
3
-----------------------------
+
+
+
, for
I
I
pkp
---------
20.0
≥
×
=
Summary of Contents for 745 TRANSFORMER MANAGEMENT RELAY
Page 30: ...2 8 745 Transformer Management Relay GE Power Management 2 3 SECURITY 2 GETTING STARTED 2 ...
Page 210: ...7 36 745 Transformer Management Relay GE Power Management 7 2 BLOCK DIAGRAMS 7 SCHEME LOGIC 7 ...
Page 322: ...9 12 745 Transformer Management Relay GE Power Management 9 3 USING 745PC 9 745 PC SOFTWARE 9 ...
Page 396: ...A 4 745 Transformer Management Relay GE Power Management A 1 FIGURES AND TABLES APPENDIXA A ...
Page 400: ...C 2 745 Transformer Management Relay GE Power Management C 1 WARRANTY INFORMATION APPENDIXC C ...
Page 406: ...vi 745 Transformer Management Relay GE Power Management ...
Page 407: ...GE Power Management 745 Transformer Management Relay NOTES ...