Date Code 20010625
Setting the Relay
9-3
SEL----311L Instruction Manual
If changes are made to the Relay or Logic settings for a setting group other than the active setting
group (see Table 9.1), the relay is not disabled while it saves the new settings. The ALARM
contact closes momentarily (for “b” contact, opens for an “a” contact; see Figure 7.26), but the
EN LED remains on (see Table 5.1) while the new settings are saved.
T
IME
-O
VERCURRENT
C
URVES
The following information describes the curve timing for the curve and time dial settings made
for the time-overcurrent elements (see Figure 3.47, 3.48 and 3.49 through Figure 3.24). The
time-overcurrent relay curves in Figure 9.1 through Figure 9.5 conform to IEEE C37.112-1996
IEEE Standard Inverse-Time Characteristic Equations for Overcurrent Relays. Figure 9.6
through Figure 9.10 represent IEC defined relay curves.
tp = operating time in seconds
tr = electromechanical induction-disk emulation reset time in seconds (if electromechanical
reset setting is made)
TD = time dial setting
M = applied multiples of pickup current [for operating time (tp), M>1; for reset time (tr), M
≤
1].
U.S. Moderately Inverse Curve: U1
U.S. Inverse Curve: U2
tp = TD • (0.0226 + 0.0104/(M
0.02
-1))
tp = TD • (0.180 + 5.95/(M
2
-1))
tr = TD • (1.08/(1-M
2
))
tr = TD • (5.95/(1-M
2
))
U.S. Very Inverse Curve: U3
U.S. Extremely Inverse Curve: U4
tp = TD • (0.0963 + 3.88/(M
2
-1))
tp = TD • (0.0352 + 5.67/(M
2
-1))
tr = TD • (3.88/(1-M
2
))
tr = TD • (5.67/(1-M
2
))
U.S. Short-Time Inverse Curve: U5
tp = TD • (0.00262 + 0.00342/(M
0.02
-1))
tr = TD • (0.323/(1-M
2
))
I.E.C. Class A Curve (Standard Inverse): C1
I.E.C. Class B Curve (Very Inverse): C2)
tp = TD • (0.14/(M
0.02
-1))
tp = TD • (13.5/(M-1))
tr = TD • (13.5/(1-M
2
))
tr = TD • (47.3/(1-M
2
))
I.E.C. Class C Curve (Extremely Inverse): C3
I.E.C. Long-Time Inverse Curve: C4
tp = TD • (80.0/(M
2
-1))
tp = TD • (120.0/(M-1))
tr = TD • (80.0/(1-M
2
))
tr = TD • (120.0/(1-M))
I.E.C. Short-Time Inverse Curve: C5
tp = TD • (0.05/(M
0.04
-1))
tr = TD • (4.85/(1-M
2
))
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