Thermal Overload
Description
The thermal overload is a condition where current higher than the rated value flows to the motor resulting in excessive heating of the motor. Rapid motor heating occurs during the overload, acceleration time, and locked rotor condition. The LTMT main unit computes the thermal memory (TM) as per the motor running current.
The thermal overload protection function generates the following signals:
-
Alarm: Thermal memory goes above the alarm level.
-
Trip: Thermal memory reaches to 100%.
-
Thermal Inhibit: When the motor is stopped and thermal memory is above the start thermal inhibit level.
The following graph shows the thermal overload protection curve:
Trip Time Chart
The thermal overload protection function supports different trip classes and service factor setting. The following tables shows the thermal overload protection trip time with respect to motor current, trip class setting, and service factor setting.
|
Service factor |
Motor current (x IFLC) |
Trip time (s) |
|||||||
|---|---|---|---|---|---|---|---|---|---|
|
Class 5 |
Class 10 |
Class 15 |
Class 20 |
Class 25 |
Class 30 |
Class 35 |
Class 40 |
||
|
1.00 |
7.20 |
3.46 |
6.91 |
10.37 |
13.83 |
17.29 |
20.74 |
24.20 |
27.66 |
|
6.00 |
5.00 |
10.00 |
15.00 |
20.00 |
25.00 |
30.00 |
35.00 |
40.00 |
|
|
5.00 |
7.25 |
14.49 |
21.74 |
28.98 |
36.23 |
43.47 |
50.72 |
57.96 |
|
|
4.00 |
11.45 |
22.91 |
34.36 |
45.82 |
57.27 |
68.73 |
80.18 |
91.64 |
|
|
3.00 |
20.91 |
41.81 |
62.72 |
83.62 |
104.53 |
125.43 |
146.34 |
167.24 |
|
|
2.00 |
51.06 |
102.12 |
153.18 |
204.24 |
255.30 |
306.36 |
357.42 |
408.48 |
|
|
1.50 |
104.33 |
208.65 |
312.98 |
417.30 |
521.63 |
625.95 |
730.28 |
834.60 |
|
|
1.00 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.05 |
7.20 |
3.82 |
7.63 |
11.45 |
15.26 |
19.08 |
22.89 |
26.71 |
30.52 |
|
6.00 |
5.52 |
11.04 |
16.56 |
22.08 |
27.60 |
33.12 |
38.64 |
44.16 |
|
|
5.00 |
8.01 |
16.01 |
24.02 |
32.02 |
40.03 |
48.03 |
56.04 |
64.04 |
|
|
4.00 |
12.67 |
25.34 |
38.02 |
50.69 |
63.36 |
76.03 |
88.70 |
101.37 |
|
|
3.00 |
23.19 |
46.39 |
69.58 |
92.78 |
115.97 |
139.16 |
162.36 |
185.55 |
|
|
2.00 |
57.23 |
114.46 |
171.69 |
228.92 |
286.15 |
343.38 |
400.61 |
457.84 |
|
|
1.50 |
119.51 |
239.02 |
358.53 |
478.04 |
597.55 |
717.06 |
836.58 |
956.09 |
|
|
1.05 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.10 |
7.20 |
4.19 |
8.38 |
12.58 |
16.77 |
20.96 |
25.15 |
29.34 |
33.54 |
|
6.00 |
6.07 |
12.14 |
18.20 |
24.27 |
30.34 |
36.41 |
42.48 |
48.55 |
|
|
5.00 |
8.81 |
17.61 |
26.42 |
35.22 |
44.03 |
52.83 |
61.64 |
70.44 |
|
|
4.00 |
13.96 |
27.91 |
41.87 |
55.83 |
69.79 |
83.74 |
97.70 |
111.66 |
|
|
3.00 |
25.63 |
51.25 |
76.88 |
102.51 |
128.13 |
153.76 |
179.38 |
205.01 |
|
|
2.00 |
63.94 |
127.88 |
191.82 |
255.76 |
319.70 |
383.64 |
447.58 |
511.53 |
|
|
1.50 |
136.97 |
273.94 |
410.91 |
547.88 |
684.85 |
821.82 |
958.79 |
1095.76 |
|
|
1.10 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.15 |
7.20 |
4.59 |
9.17 |
13.76 |
18.35 |
22.93 |
27.52 |
32.11 |
36.69 |
|
6.00 |
6.64 |
13.29 |
19.93 |
26.57 |
33.22 |
39.86 |
46.50 |
53.14 |
|
|
5.00 |
9.65 |
19.29 |
28.94 |
38.59 |
48.23 |
57.88 |
67.53 |
77.17 |
|
|
4.00 |
15.31 |
30.62 |
45.94 |
61.25 |
76.56 |
91.87 |
107.19 |
122.50 |
|
|
3.00 |
28.21 |
56.42 |
84.62 |
112.83 |
141.04 |
169.25 |
197.46 |
225.67 |
|
|
2.00 |
71.25 |
142.49 |
213.74 |
284.98 |
356.23 |
427.47 |
498.72 |
569.97 |
|
|
1.50 |
157.29 |
314.58 |
471.87 |
629.16 |
786.44 |
943.73 |
1101.02 |
1258.31 |
|
|
1.15 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.20 |
7.20 |
5.00 |
10.00 |
15.00 |
20.00 |
25.00 |
30.00 |
35.00 |
40.00 |
|
6.00 |
7.25 |
14.49 |
21.74 |
28.98 |
36.23 |
43.47 |
50.72 |
57.96 |
|
|
4.00 |
16.74 |
33.48 |
50.22 |
66.96 |
83.70 |
100.43 |
117.17 |
133.91 |
|
|
3.00 |
30.95 |
61.89 |
92.84 |
123.78 |
154.73 |
185.67 |
216.62 |
247.57 |
|
|
2.00 |
79.21 |
158.42 |
237.63 |
316.84 |
396.05 |
475.26 |
554.48 |
633.69 |
|
|
1.50 |
181.33 |
362.66 |
543.99 |
725.32 |
906.66 |
1087.99 |
1269.32 |
1450.65 |
|
|
1.20 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.25 |
7.20 |
5.43 |
10.86 |
16.30 |
21.73 |
27.16 |
32.59 |
38.02 |
43.46 |
|
6.00 |
7.88 |
15.75 |
23.63 |
31.50 |
39.38 |
47.25 |
55.13 |
63.01 |
|
|
5.00 |
11.45 |
22.91 |
34.36 |
45.82 |
57.27 |
68.73 |
80.18 |
91.64 |
|
|
4.00 |
18.24 |
36.48 |
54.72 |
72.95 |
91.19 |
109.43 |
127.67 |
145.91 |
|
|
3.00 |
33.85 |
67.69 |
101.54 |
135.38 |
169.23 |
203.07 |
236.92 |
270.76 |
|
|
2.00 |
87.91 |
175.83 |
263.74 |
351.65 |
439.57 |
527.48 |
615.40 |
703.31 |
|
|
1.50 |
210.43 |
420.87 |
631.30 |
841.74 |
1052.17 |
1262.61 |
1473.04 |
1683.47 |
|
|
1.25 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.30 |
7.20 |
5.88 |
11.77 |
17.65 |
23.53 |
29.41 |
35.30 |
41.18 |
47.06 |
|
6.00 |
8.53 |
17.07 |
25.60 |
34.14 |
42.67 |
51.20 |
59.74 |
68.27 |
|
|
5.00 |
12.42 |
24.85 |
37.27 |
49.69 |
62.12 |
74.54 |
86.96 |
99.38 |
|
|
4.00 |
19.81 |
39.63 |
59.44 |
79.25 |
99.07 |
118.88 |
138.69 |
158.50 |
|
|
3.00 |
36.91 |
73.83 |
110.74 |
147.66 |
184.57 |
221.49 |
258.40 |
295.31 |
|
|
2.00 |
97.45 |
194.90 |
292.35 |
389.80 |
487.25 |
584.70 |
682.15 |
779.59 |
|
|
1.50 |
246.84 |
493.68 |
740.52 |
987.37 |
1234.21 |
1481.05 |
1727.89 |
1974.73 |
|
|
1.30 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.35 |
7.20 |
6.35 |
12.70 |
19.06 |
25.41 |
31.76 |
38.11 |
44.47 |
50.82 |
|
6.00 |
9.22 |
18.44 |
27.66 |
36.88 |
46.10 |
55.32 |
64.55 |
73.77 |
|
|
5.00 |
13.43 |
26.87 |
40.30 |
53.74 |
67.17 |
80.61 |
94.04 |
107.48 |
|
|
4.00 |
21.46 |
42.93 |
64.39 |
85.86 |
107.32 |
128.78 |
150.25 |
171.71 |
|
|
3.00 |
40.16 |
80.32 |
120.48 |
160.64 |
200.80 |
240.97 |
281.13 |
321.29 |
|
|
2.00 |
107.93 |
215.87 |
323.80 |
431.73 |
539.67 |
647.60 |
755.54 |
863.47 |
|
|
1.50 |
294.76 |
589.52 |
884.28 |
1179.04 |
1473.80 |
1768.56 |
2063.32 |
2358.08 |
|
|
1.35 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.40 |
7.20 |
6.84 |
13.68 |
20.52 |
27.36 |
34.20 |
41.04 |
47.89 |
54.73 |
|
6.00 |
9.94 |
19.87 |
29.81 |
39.75 |
49.68 |
59.62 |
69.55 |
79.49 |
|
|
5.00 |
14.49 |
28.98 |
43.47 |
57.96 |
72.45 |
86.95 |
101.44 |
115.93 |
|
|
4.00 |
23.19 |
46.39 |
69.58 |
92.78 |
115.97 |
139.16 |
162.36 |
185.55 |
|
|
3.00 |
43.59 |
87.19 |
130.78 |
174.38 |
217.97 |
261.56 |
305.16 |
348.75 |
|
|
2.00 |
119.51 |
239.02 |
358.53 |
478.04 |
597.55 |
717.06 |
836.58 |
956.09 |
|
|
1.50 |
363.64 |
727.28 |
1090.92 |
1454.56 |
1818.19 |
2181.83 |
2545.47 |
2909.11 |
|
|
1.40 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.45 |
7.20 |
7.35 |
14.70 |
22.05 |
29.39 |
36.74 |
44.09 |
51.44 |
58.79 |
|
6.00 |
10.68 |
21.36 |
32.04 |
42.72 |
53.40 |
64.08 |
74.77 |
85.45 |
|
|
5.00 |
15.59 |
31.18 |
46.78 |
62.37 |
77.96 |
93.55 |
109.14 |
124.74 |
|
|
4.00 |
25.00 |
50.01 |
75.01 |
100.02 |
125.02 |
150.03 |
175.03 |
200.04 |
|
|
3.00 |
47.22 |
94.45 |
141.67 |
188.89 |
236.12 |
283.34 |
330.56 |
377.79 |
|
|
2.00 |
132.36 |
264.73 |
397.09 |
529.45 |
661.82 |
794.18 |
926.54 |
1058.91 |
|
|
1.50 |
483.63 |
967.26 |
1450.89 |
1934.52 |
2418.15 |
2901.78 |
3385.41 |
3869.04 |
|
|
1.45 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
|
1.50 |
7.20 |
7.88 |
15.75 |
23.63 |
31.50 |
39.38 |
47.25 |
55.13 |
63.01 |
|
6.00 |
11.45 |
22.91 |
34.36 |
45.82 |
57.27 |
68.73 |
80.18 |
91.64 |
|
|
5.00 |
16.74 |
33.48 |
50.22 |
66.96 |
83.70 |
100.43 |
117.17 |
133.91 |
|
|
4.00 |
26.90 |
53.80 |
80.69 |
107.59 |
134.49 |
161.39 |
188.29 |
215.19 |
|
|
3.00 |
51.06 |
102.12 |
153.18 |
204.24 |
255.30 |
306.36 |
357.42 |
408.48 |
|
|
2.00 |
146.73 |
293.45 |
440.18 |
586.90 |
733.63 |
880.35 |
1027.08 |
1173.81 |
|
|
1.50 |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
No trip |
|
Parameter Settings
 CAUTION |
|---|
|
HAZARD OF MOTOR OVERHEATING
The Motor Trip Class parameter must be set to the thermal
heating characteristics of the motor. Refer to the motor manufacturers
instructions before setting this parameter.
Failure to follow these instructions can result in injury or equipment damage.
|
The thermal overload protection function has the following configurable settings:
|
Parameter |
Setting range |
Default value |
|---|---|---|
|
Function |
|
Alarm + Trip |
|
Service Factor |
1.00–1.50 in step of 0.05 |
1.15 |
|
Trip Class |
5, 10, 15, 20, 25, 30, 35, 40 |
10 |
|
Alarm Level |
80–100% of thermal memory in step of 5% |
80% TM |
|
Reset Mode |
|
Auto |
|
Thermal Reset Level |
30–95% of thermal memory in step of 5% |
90% TM |
|
Start Inhibit Level |
5–100% of thermal memory in step of 5% |
90% TM |
|
Auxiliary Fan |
|
Disable |
|
Cool Down Function |
|
Disable |
|
Cool Down Time |
0.0–6000.0 s in step of 0.1 s |
0.0 s |
|
Pause Function |
|
Disable |
|
Pause Time |
0.0–6000.0 s in step of 0.1 s |
0.0 s |
|
Block Function |
|
Disable |
|
Block Level |
80–95% of thermal memory in step of 5% |
80% |
|
Block Time |
0.0–6000.0 s in step of 0.1 s |
0.0 s |
Service Factor
Service factor of the motor is configurable from 1.00 to 1.50 as per the motor name plate.
Trip Class
Select the trip class as per the motor characteristics. The LTMT main unit provides thermal overload protection for eight different trip classes – Class 5, Class 10, Class 15, Class 20, Class 25, Class 30, Class 35, Class 40.
Refer to Trip Time Chart for selection of trip class and service factor.
Alarm Level
Alarm level of thermal overload protection is configurable from 80% to 100% of thermal memory. The LTMT main unit generates the alarm signal once the thermal memory goes beyond the alarm level.
Thermal Reset Level
Thermal overload trip can be reset if the thermal memory goes below the thermal reset level.
Start Inhibit Level
Start inhibit level is used to detect the thermal inhibit condition. If the thermal memory goes above the start inhibit level, the thermal inhibit cause is set.
Cool Down Function
Cool down function allows you to reset the thermal memory with configured cool down time.
If the cool down function is enabled and motor is tripped due to thermal overload, thermal memory resets to zero after cool down time has elapsed.
Pause Function
Pause function allows you to reset the thermal memory with the configured pause time, if the motor is not tripped due to thermal overload.
If the pause function is enabled and the motor is not tripped due to thermal overload, thermal memory will reset to zero after the pause time has elapsed.
Block Function
Block function allows you
to block the thermal overload protection for the configured block
time during the motor start. This function blocks the thermal memory
(TM) at the block level. For more information, refer to the below
graphical representation.
| A | Motor stop |
| B | Block time |
| C | Block level |
Auxiliary Fan
If the auxiliary fan is enabled, thermal memory will cool down four times faster. This mode is not suitable with cool down function and pause function.