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S3 PROTECTION
MOTOR
STANDARD CURVE MULTIPLIERS
CURRENT
× 1
× 2
× 3
(× FLA)
1.01
4353.6 8707.2 13061 17414 21768 26122 30475 34829 39183 43536 47890 52243 56597 60951 65304
1.05
853.71 1707.4 2561.1 3414.9 4268.6 5122.3 5976.0 6829.7 7683.4 8537.1 9390.8 10245 11098 11952 12806
1.10
416.68 833.36 1250.0 1666.7 2083.4 2500.1 2916.8 3333.5 3750.1 4166.8 4583.5 5000.2 5416.9 5833.6 6250.2
1.20
198.86 397.72 596.58 795.44 994.30 1193.2 1392.0 1590.9 1789.7 1988.6 2187.5 2386.3 2585.2 2784.1 2982.9
1.30
126.80 253.61 380.41 507.22 634.02 760.82 887.63 1014.4 1141.2 1268.0 1394.8 1521.6 1648.5 1775.3 1902.1
1.40
91.14
182.27 273.41 364.55 455.68 546.82 637.96 729.09 820.23 911.37 1002.5 1093.6 1184.8 1275.9 1367.0
1.50
69.99
139.98 209.97 279.96 349.95 419.94 489.93 559.92 629.91 699.90 769.89 839.88 909.87 979.86 1049.9
1.75
42.41
84.83
127.24 169.66 212.07 254.49 296.90 339.32 381.73 424.15 466.56 508.98 551.39 593.81 636.22
2.00
29.16
58.32
87.47
2.25
21.53
43.06
64.59
2.50
16.66
33.32
49.98
2.75
13.33
26.65
39.98
3.00
10.93
21.86
32.80
3.25
9.15
18.29
27.44
3.50
7.77
15.55
23.32
3.75
6.69
13.39
20.08
4.00
5.83
11.66
17.49
4.25
5.12
10.25
15.37
4.50
4.54
9.08
13.63
4.75
4.06
8.11
12.17
5.00
3.64
7.29
10.93
5.50
2.99
5.98
8.97
6.00
2.50
5.00
7.49
6.50
2.12
4.24
6.36
7.00
1.82
3.64
5.46
7.50
1.58
3.16
4.75
8.00
1.39
2.78
4.16
10.00
1.39
2.78
4.16
15.00
1.39
2.78
4.16
20.00
1.39
2.78
4.16
6–62
Table 1: Standard overload curve trip times (in seconds)
× 4
× 5
× 6
× 7
116.63 145.79 174.95 204.11 233.26 262.42 291.58 320.74 349.90 379.05 408.21 437.37
86.12
107.65 129.18 150.72 172.25 193.78 215.31 236.84 258.37 279.90 301.43 322.96
66.64
83.30
99.96
116.62 133.28 149.94 166.60 183.26 199.92 216.58 233.24 249.90
53.31
66.64
79.96
93.29
43.73
54.66
65.59
76.52
36.58
45.73
54.87
64.02
31.09
38.87
46.64
54.41
26.78
33.47
40.17
46.86
23.32
29.15
34.98
40.81
20.50
25.62
30.75
35.87
18.17
22.71
27.25
31.80
16.22
20.28
24.33
28.39
14.57
18.22
21.86
25.50
11.96
14.95
17.94
20.93
9.99
12.49
14.99
17.49
8.48
10.60
12.72
14.84
7.29
9.11
10.93
12.75
6.33
7.91
9.49
11.08
5.55
6.94
8.33
9.71
5.55
6.94
8.33
9.71
5.55
6.94
8.33
9.71
5.55
6.94
8.33
9.71
Table 2: Conversion Between NEMA Curves and 339 Curve Multiplier
NEMA Curve
339 Curve Multiplier
UNBALANCE BIASING
Unbalanced phase currents, that is to say negative sequence currents, cause rotor heating
in addition to the normal heating caused by positive sequence currents. When the motor
is running, the rotor rotates in the direction of the positive-sequence Magnetomotive Force
(MMF) wave at near synchronous speed. The induced rotor currents are at a frequency
determined by the difference between synchronous speed and rotor speed, typically 2 to 4
Hertz. At these low frequencies the current flows equally in all parts of the rotor bars, right
down to the inside portion of the bars at the bottom of the slots. Negative-sequence stator
current on the other hand causes an MMF wave with a rotation opposite to rotor rotation,
which induces rotor current with a frequency approximately 2 times the line frequency:
100 Hz for a 50 Hz system or 120 Hz for a 60 Hz system. The skin effect at this frequency
restricts the rotor current to the outside portion of the bars at the top of the slots, causing
× 8
× 9
× 10
106.62 119.95 133.27 146.60 159.93 173.25 186.58 199.91
87.46
98.39
109.32 120.25 131.19 142.12 153.05 163.98
73.16
82.31
91.46
62.19
69.96
77.73
53.56
60.25
66.95
46.64
52.47
58.30
41.00
46.12
51.25
36.34
40.88
45.42
32.44
36.50
40.55
29.15
32.79
36.43
23.91
26.90
29.89
19.99
22.48
24.98
16.96
19.08
21.20
14.57
16.39
18.21
12.66
14.24
15.82
11.10
12.49
13.88
11.10
12.49
13.88
11.10
12.49
13.88
11.10
12.49
13.88
Class 10
Class 15
4
6
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS
× 11
× 12
× 13
× 14
100.60 109.75 118.89 128.04 137.18
85.51
93.28
101.05 108.83 116.60
73.64
80.34
87.03
93.73
64.13
69.96
75.79
81.62
56.37
61.50
66.62
71.75
49.97
54.51
59.05
63.59
44.61
48.66
52.72
56.77
40.08
43.72
47.36
51.01
32.88
35.87
38.86
41.85
27.48
29.98
32.48
34.97
23.32
25.44
27.55
29.67
20.04
21.86
23.68
25.50
17.41
18.99
20.57
22.15
15.27
16.65
18.04
19.43
15.27
16.65
18.04
19.43
15.27
16.65
18.04
19.43
15.27
16.65
18.04
19.43
Class 20
Class 30
8
12
× 15
100.42
87.45
76.87
68.14
60.83
54.65
44.84
37.47
31.79
27.32
23.74
20.82
20.82
20.82
20.82
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