Lenze DSD Bedienungsanleitung PDF herunterladen (Seite 352)

11 Drive Dimensioning

11.6 Inverters

352

Lenze · Drive Solution Designer · Manual · DMS 4.2 EN · 12/2013 · TD23

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

11.6.1.6 Current derating for inverters

If small field frequencies (3 ... 5 Hz) occur, the max. output current is limited for some inverters. The

torque calculated is no longer reached.

Effects

• Applications with low field frequencies

( 438)

• The current derating has a more serious impact on synchronous machines than on asynchro-

nous machines. Due to the missing slip frequency, in the case of asynchronous machines the 5

Hz threshold is not exceeded so quickly.

• During operation in generator mode the current derating is more distinct than during operation

in motor mode.

• If an output current above the standstill current is required for horizontal drives:

• Acceleration movements: The acceleration distance or time will be slightly longer.

• Braking processes: The braking distance slightly increases.

• DC-injection braking: The braking current is reduced, and thus the braking torque provided

by the inverter is reduced.

• Extruder drives which are accelerated to the target speed during a "cold start" have no notice-

able torque reduction within the first minutes during the acceleration phase and following

constant speed phase. The pinch effect with regard to the current, which might possibly oc-

cur should be taken into consideration during the dimensioning. This applies in particular to

great drive powers, since the slip frequency usually decreases with an increasing rated motor

power.

• Slip frequencies of 4-pole asynchronous machines (example):

 Note!

The specific restrictions due to the current derating can be found in the respective docu-

mentation for the inverter.

Slip speed n

– n

)

Resulting slip frequency f

90 kW 1480 rpm (1500 – 1480) rpm = 20 rpm 0.67 Hz

22 kW 1456 rpm (1500 – 1456) rpm = 44 rpm 1.47 Hz

4 kW 1435 rpm (1500 – 1435) rpm = 65 rpm 2.17 Hz

 Note!

The DSD takes the output currents specified in the documentation of the inverter

> |5 Hz|) as a basis for calculation, and not the standstill currents.

• For passive loads a torque reduction only has a small effect on a greater following er-

ror, and it has no interfering effects on most applications.

1 2 ... 347 348 349 350 351 352 353 354 355 356 357 ... 495 496

Kommentare zu diesen Handbüchern

Keine Kommentare

Lenze DSD Bedienungsanleitung Seite 352

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Software Lenze DSD