Current Elements; Inverse Time Overcurrent Curves - GE 845 Instruction Manual

CHAPTER 4: SETPOINTS

Current Elements

Inverse Time
Overcurrent Curves
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 4-52: Current Elements Display Hierarchy
Description
The relay has six setpoint groups. The programming of the time-current characteristics of
these elements is identical in all cases and is only covered in this section. The required
curve is established by programming a Pickup Current, Curve Shape, Curve Multiplier, and
Reset Time. The Curve Shape can be either a standard shape or a user-defined shape
programmed with the FlexCurve feature. Accurate coordination may require changing the
time overcurrent characteristics of particular elements under different conditions.
The Inverse Time Overcurrent Curves used by the Time Overcurrent elements are the IEEE,
2
IEC, GE Type IAC, ANSI, I t and I
coordination with downstream devices.
If none of these curve shapes is adequate, FlexCurves™ may be used to customize the
inverse time curve characteristics. The definite time curve is also an option that may be
appropriate if only simple protection is required.
Table 4-23: OVERCURRENT CURVE TYPES
IEEE ANSI
IEEE Extremely ANSI Extremely
Inverse Inverse
IEEE Very Inverse ANSI Very Inverse IEC Curve B (BS
IEEE Moderately ANSI Normally
Inverse Inverse
ANSI Moderately
Inverse
4
t standard curve shapes. This allows for simplified
IEC GE TYPE IAC
IEC Curve A (BS IAC Extremely
142) Inverse
IAC Very Inverse
142)
IEC Curve C (BS IAC Inverse
142)
IEC Short Inverse IAC Short Inverse
PROTECTION
OTHER
2
I t
4
I t
FlexCurves™ A, B,
C and D
Recloser Curve
Definite Time
4–153