8 Additional information
BU 0800 en-4521 139
8.2 Reduced output power
The frequency inverters are designed for special overload situations. For example, 1.5x overcurrent
can be used for 60 s. For approx. 3.5 s, 2x overcurrent is possible. A reduction of the overload
capacity or its duration must be considered for the following circumstances:
• Output frequencies < 4.5 Hz and DC voltage (stationary pointer)
• Pulse frequencies greater than the nominal pulse frequency (P504)
• Increased mains voltages > 400 V
• Increased heat sink temperature
The following characteristic curves can be used to obtain the corresponding current/power limit.
8.2.1 Derating depending on the pulse frequency
This illustration shows how the output current must be reduced, depending on the pulse frequency in
order to avoid excessive heat dissipation in the frequency inverter. Reductions starts at 6 kHz.
With the applicable rated current of Figure 3, a differentiation must be made between wall-mounted
and motor-mounted inverters. In case of wall-mounting, the graph below applies and the inverter rated
current may be taken as IN.
For a motor-mounted frequency inverter, the internal temperature of 90 °C is decisive and must not be
exceeded. The graph in Figure 3 only serves as a reference point where IN corresponds to the rated
motor current.
The diagram shows the possible current load capacity for continuous operation.
Figure 3: Heat losses due to pulse frequency
pulse
pulse
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