Lenze i700 - Manual (Page 236)

8 Monitoring functions
8.2 Monitoring of the power section and device utilisation (Ixt)
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Lenze · i700 servo inverter · Reference manual · DMS 1.5 EN · 03/2014 · TD05
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8.2 Monitoring of the power section and device utilisation (Ixt)
The monitoring of the device utilisation primarily protects the power section. Indirectly, also other
components such as conductors and terminals are protected. The monitoring system is designed as
simply as possible, in order to facilitate the determination of the reserves until disconnection, and
to carry out the drive dimensioning accordingly. Only cycles the arithmetic mean (AV) of which does
not exceed the continuous device current are permissible.
The motor current is evaluated depending on the continuously permissible rated current at the
effective switching frequency and mains voltage and is provided to two PT1 timing elements:
• The PT1 timing element with a time constant of t = 3.3 s simulates the thermal response of the
power section (power semiconductor).
• The PT1 timing element with a time constant of t = 60 s serves to monitor the cycle with
maximum current in order to protect the device from thermal overload (heatsink temperature).
[8-1] Ixt monitoring signal flow
The outputs of the two PT1 timing elements show the current utilization of power section and the
entire device.
Gain factors and filter time constants are defined such that within a certain cycle time a specific
overload current can be active for a certain period with subsequent recovery phase (75 % rated
current).
The following load change cycles are defined for the i700 servo inverter:
• 15-second cycle:
200 % rated current for 3 s, recovery phase 12 s with 75 % rated current
• 24-second cycle:
175 % rated current for 6 s, recovery phase 18 s with 75 % rated current
• 3-minute cycle:
150 % rated current for 60 s, recovery phase 120 s with 75 % rated current
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"i700 servo inverter" hardware manual
In order to determine the reserves until Ixt disconnection, the rated data depending on
the switching frequency and mains operation such as the rated device current and
maximum current for the respective i700 design can be gathered from the hardware
manual. (See chapter 4.2.4 "Axis modules" and chapter 4.3 "Overcurrent operation".)
0x2D40:1 | 0x3540:1
0x2D40:4 | 0x3540:4
t = 3.3 s
t = 60 s
I
mot
Powerstage utilisation (Ixt): Act. value
Device utilisation (Ixt): Act. value
Gain = 66 %
Gain = 80 %