Standard inverse-time characteristics - Arc protection - Motor protection - Feeder protection - Back-up protection - Technical Manual - REX610 Protection and control - 1.2 - IEC - ANSI - 17.02.2023

REX610 Technical Manual

For inverse-time operation, both IEC and ANSI/IEEE standardized inverse-time characteristics are supported.

The operate times for the ANSI and IEC IDMT curves are defined with the coefficients A, B and C.

The values of the coefficients can be calculated according to the formula:

Figure 1. Equation
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t[s] Operate time in seconds
I Measured current
I> Set Start value
k Set Time multiplier
Table 1. Curve parameters for ANSI and IEC IDMT curves
Curve name A B C
(1) ANSI Extremely Inverse 28.2 0.1217 2.0
(2) ANSI Very Inverse 19.61 0.491 2.0
(3) ANSI Normal Inverse 0.0086 0.0185 0.02
(4) ANSI Moderately Inverse 0.0515 0.1140 0.02
(6) Long Time Extremely Inverse 64.07 0.250 2.0
(7) Long Time Very Inverse 28.55 0.712 2.0
(8) Long Time Inverse 0.086 0.185 0.02
(9) IEC Normal Inverse 0.14 0.0 0.02
(10) IEC Very Inverse 13.5 0.0 1.0
(11) IEC Inverse 0.14 0.0 0.02
(12) IEC Extremely Inverse 80.0 0.0 2.0
(13) IEC Short Time Inverse 0.05 0.0 0.04
(14) IEC Long Time Inverse 120 0.0 1.0
Figure 2. ANSI extremely inverse-time characteristics
Figure 3. ANSI very inverse-time characteristics
Figure 4. ANSI normal inverse-time characteristics
Figure 5. ANSI moderately inverse-time characteristics
Figure 6. ANSI long-time extremely inverse-time characteristics
Figure 7. ANSI long-time very inverse-time characteristics
Figure 8. ANSI long-time inverse-time characteristics
Figure 9. IEC normal inverse-time characteristics
Figure 10. IEC very inverse-time characteristics
Figure 11. IEC inverse-time characteristics
Figure 12. IEC extremely inverse-time characteristics
Figure 13. IEC short-time inverse-time characteristics
Figure 14. IEC long-time inverse-time characteristics