Lenze EDB9300UES - Manual (Page 36)

Technical Data
BA8230 31
2.5.4 Motor filters and output chokes
2.5.4.1 Motor filters The use of the latest semiconductor technology allows extremely short times for
switching the circuit breakers in frequency inverters on or off.
8230 frequency inverter are IGBT pulse inverters whose output voltage has rising or
falling flanks of approx. 2 ... 3 kV/µs.
Output filters for 8230 frequency inverter units are available for unlimited use with the
benefits of IGBT technology when using a wide range of asynchronous 3-phase
motors with different winding insulation voltages. These filters reduce the voltage rate
of rise. An excessive voltage rise at the motor terminal box is determined by the cable
length and the windings on the 3-phase motor used, through capacitive coupling.
8230 frequency inverter motor filters reduce this excessive rise in voltage through
their built-in attenuation circuit. The 8230 frequency inverter motor filter prevents
premature ageing of the insulation and therefore early failure if insulation limits are
exceeded.
In general:
du/dt
→
The shorter the motor cable length, the more critical
the rate of rise
Excessive voltage rise
→
When longer motor cables are used the amplitude of
the voltage rise and fall at the motor terminal box can
increase beyond the critical value for the mains supply
voltage.
Higher cable inductance and capacitance on longer motor cables, however, reduces
the du/dt value. The maximum voltage amplitude is therefore also reduced, so that the
voltage rate of rise is reduced when an inductance due to longer cables applies.
The motor du/dt filters developed for 8230 frequency inverter units reduce the output
voltage rise and fall times to below 500 V/µs (VDE 0503T1 Sheet 2). At the same time
the filter design limits the rise time and the amplitude of the voltages and currents
occurring in comparison to earth potential.
When using screened motor cable a du/dt filter also attenuates the amplitude and rate
of rise of the screen current. This significantly reduces the effects of adjacent
unscreened cables.
The limit for transient overvoltages is maintained when the cable lengths specified for
the filter are observed.
Fig. 11: Permitted limits for motor insulation
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