Definite Time Curve; Iec Curves - GE 745 TRANSFORMER MANAGEMENT RELAY Instruction Manual

5 SETPOINTS
The Definite Time curve shape causes a trip as soon as the pickup level is exceeded for a specified period of
time. The base Definite Time curve has a delay of 0.1 seconds. The curve multiplier makes this delay adjust-
able from 0.000 to 10.000 seconds in steps of 0.001 seconds.
For European applications, the relay offers the four standard curves defined in IEC 255-4 and British standard
BS142. These are defined as IEC Curve A, IEC Curve B, IEC Curve C, and Short Inverse. The formula for
these curves is:
where: T = Operate Time (seconds)
M = Multiplier Setpoint
I = Input Current
I = Pickup Current Setpoint
pkp
K , E = Constants
Table 5–12: IEC CURVE CONSTANTS
IEC (BS) CURVE SHAPE
IEC CURVE A (BS142)
IEC CURVE B (BS142)
IEC CURVE C (BS142)
IEC SHORT INVERSE
GE Power Management

K
×
M ---------------------------- - ,

( )
E
1.03 – 1



K
×
M -------------------------------- ,

T
=
( ⁄ )
E
I I
– 1

pkp


K
×
 M ---------------------------- - ,
( )
E
 20.0 1
–
CONSTANTS
K E
0.140 0.020
13.500 1.000
80.000 2.000
0.050 0.040
745 Transformer Management Relay
5.9 TIME OVERCURRENT CURVES

5.9.3 DEFINITE TIME CURVE

I
≤ <
1 1.03
---------
I
pkp
I
≤ <
1.03 --------- 20.0
I
pkp
I
≥
20.0
---------
I
pkp

5.9.4 IEC CURVES

5
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