Eaton MMX11 Series - Idle Power Compensation Devices; Mains Reactors

04/10 MN04020001Z-EN
Electrical power network
25
Total harmonic distortion (THD)
The THD (Total Harmonic Distortion) is a measurement for the
occurring harmonic distortion of the sinusoidal oscillation (mains
power side) input variables with the frequency inverter. It is given
in percent of the total value.
With the frequency inverters of the M-Max
TM
series, the permitted
value for the total harmonic distortion THD >120 %.
Idle power compensation devices
Compensation on the power supply side is not required for the
frequency inverters of the M-MAX
TM
series. From the AC power
supply network they only take on very little reactive power of the
fundamental harmonics (cos
v ~ 0.98).
Mains reactors
A mains reactor (also called commutation inductors) increases the
inductance of the power supply line. This extends the current flow
period and dampens mains deviations.
On frequency inverters, a mains reactor limits the mains feedback
to permissible values. The harmonic current emissions that are fed
back into the mains network ("mains feedback") are reduced. This
reduces the mains-side apparent current to about 30 %.
Towards the frequency inverter, the mains reactors dampen the
interference from the supply network. This increases the withstand
voltage of the frequency inverter and lengthens the lifespan
(diodes of the mains power rectifier, intermediate circuit
capacitors).
Mains reactors are designed based on the mains-side input current
(I
LN
) of the frequency inverter. Mains chokes and the assignment
to M-MAX
TM
frequency inverters are explained in the appendix.
U
1
= fundamental component
THD k = 0.1 l K = 10 % ~ -20 dB (THD suppression)
THD (Total Harmonic Distortion)
h
In the AC power networks with non-choked idle current
compensation devices, current deviations can enable
parallel resonance and undefinable circumstances.
In the project planning for the connection of frequency
inverters to AC power networks with undefined
circumstances, consider using main chokes.
K
U
2
2
U+
3
2
U
4
2
 U
n
++
2
+
U
1
2
U+
2
2
U
3
2
U
4
2
 U
n
++
2
++
-------------------------------------------------------------------------------------------
100%=
THD
U
2
2
U+
3
2
U
4
2
 U
n
++
2
+
U
1
------------------------------------------------------------------------------=
h
For the operation of the M-MAX
TM
frequency inverter, the
application of main chokes is not necessary.
We do recommend however that an upstream main choke
is used since the network quality is not known in most
cases.
While planning the project, consider that a mains reactor
is only assigned to a single frequency inverter for
isolation. Using a large mains reactor for multiple small
frequency inverters should therefore be avoided if at all
possible.
When using an adapting transformer (assigned to a single
frequency inverter), a main choke is not necessary.