RFL Electronics RFL 9300 - Time-Overcurrent Curve Equations

RFL 9300 RFL Electronics Inc.
January 30, 2002 6-67 (973) 334-3100
6.8 TIME-OVERCURRENT CURVE EQUATIONS
Both US and IEC time-overcurrent curves are provided in the RFL 9300 relay. Use the PROGRAM mode to
select the curve characteristics you desire. These time curve equations are valid for all time-overcurrent ele-
ments. Plots showing operating time versus multiples of pickup current are shown on the following pages. The
equations and curves apply while the product of the multiples of pickup and pickup setting is less than
32 x I
(nominal)
amps, secondary.
6.8.1 EQUATIONS FOR US CURVES
t
M
= curve operating time in seconds
TD = time dial setting
M = multiples of pickup. For curve operating time (t
M
), M > 1.
Curve USA1: Moderately Inverse - See Figure 6-33
t
M
= TD [ 0.0226 + 0.0104/(M
0.02
- 1) ]
Curve USA2: Inverse - See Figure 6-34
t
M
= TD [ 0.180 + 5.95/(M
2
- 1) ]
Curve USA3: Very Inverse - See Figure 6-35
t
M
= TD [ 0.0963 + 3.88/(M
2
- 1) ]
Curve USA4: Extremely Inverse - See Figure 6-36
t
M
= TD [ 0.0352 + 5.67/(M
2
- 1) ]