5 reduced output power, 2 reduced overcurrent due to time, Reduced output power – NORD Drivesystems BU0505 User Manual
Page 172: Increased heat dissipation due to pulse frequency, Reduced overcurrent due to time, Fig. 16: heat losses due to pulse frequency
SK 54xE – Users Manual for Frequency Inverters
172
BU 0505 GB-1013
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8.5 Reduced output power
The frequency inverters are designed for certain overload situations. For example, 1.5x overcurrent
can be used for 60 sec. For approx. 3.5 sec a 2x overcurrent is possible. A reduction of the overload
capacity or its time must be taken into account in the following circumstances:
o
Output frequencies < 4.5 Hz and constant voltages (needle stationary)
o
Pulse frequencies greater than the nominal pulse frequency (P504)
o
Increased mains voltage > 400V
o
Increased heat sink temperature
On the basis of the following characteristic curves, the particular current / power limitation can be read
off.
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8.5.1 Increased heat dissipation due to pulse frequency
This illustration shows how the output current must be reduced, depending on the pulse frequency for
230V and 400V devices, in order to avoid excessive heat dissipation in the frequency inverter.
For 400V devices, the reduction begins at a pulse frequency above 6kHz. For 230V devices, the
reduction begins at a pulse frequency above 8kHz.
Even with increased pulse frequencies the frequency inverter is capable of supplying its maximum
peak current, however only for a reduced period of time. The diagram shows the possible current load
capacity for continuous operation.
1.2
0.4
k 400V f puls
k 230V f puls
16
3
f puls
4
6
8
10
12
14
16
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
I / I
N
Pulse frequency [kHz]
Fig. 16: Heat losses due to pulse frequency
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8.5.2 Reduced overcurrent due to time
The possible overload capacity changes depending on the duration of an overload. Several values are
cited in this table. If one of these limiting values is reached, the frequency inverter must have sufficient
time (with low utilisation or without load) in order to regenerate itself.
If operated repeatedly in the overload region at short intervals, the limiting values stated in the tables
are reduced.