Motor Protection By I 2 T Monitoring - BONFIGLIOLI ACTIVE CUBE 201 Operating Instructions Manual

In the calculation of the triggering time, the output current measured in working points below the
frequency limit will be valued at a factor between 1 and 2.
This factor is determined depending on the stator frequency. In this way, the higher thermal load of
self-ventilated motors in the lower speed range is considered.
The table shows an extract of the factors for a 50 Hz motor.
300%
0 200%
5 188%
10 177%
20 160%
30 147%
50 129%
100 106%
150 100%
19.5.2 Motor protection by I
I2t monitoring is another way to protect the motor against thermal overload. This motor protection
method is mainly used in servo systems.
Wherever synchronous servomotors are used, I2t monitoring is a proven alternative to motor circuit
breakers. By integrating measurable or known motor parameters, heat-up is modeled based on a
mathematical model.
The I2t monitoring feature can be selected via Operation Mode 571.
The settings are data set change-over settings.
I²t monitoring is done, as shown in the illustration, via (Iact/Irated)².
The monitored variable is valued via a PT1 element with the thermal time constant of the stator. If
the PT1 element output exceeds 120%, an error message will be reported and the inverter will shut
down. The 120% threshold ensures the overshooting will not result in immediate shutdown.
Permanent exceeding of the 100% load of the stator winding should be avoided in the application.
242
Frequency Limit 572
200% 150% 100%
200% 200% 200%
182% 177% 168%
168% 160% 147%
147% 137% 122%
132% 122% 109%
114% 106% 100%
100% 100% 100%
100% 100% 100%
2
t monitoring
Operating Instructions ACU
80% 60% 40%
200% 200% 200%
162% 153% 139%
139% 129% 114%
114% 106% 100%
103% 100% 100%
100% 100% 100%
100% 100% 100%
100% 100% 100%
20% 10%
200% 200%
114% 100%
100% 100%
100% 100%
100% 100%
100% 100%
100% 100%
100% 100%
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