5 Selection of Advanced Harmonic Filter
This chapter helps selecting the right filter size and
contains calculation examples, electrical data, and order
number for the filters.
5.1 Selecting the Correct AHF
For optimal performance, size the VLT
®
Advanced
Harmonic Filter AHF 005/AHF 010 for the mains input
current to the frequency converter. This current is the
input current drawn based on the expected load of the
frequency converter and not on the size of the frequency
converter itself.
5.1.1 How to Calculate the Correct Filter
Size
Calculate the mains input current of the frequency
converter (I
FC,L
). Use the nominal motor current (I
M,N
) and
the displacement factor (Cos
φ
) of the motor for the
calculation. Both values are normally printed on the
nameplate of the motor. If the nominal motor voltage
(U
M,N
) is unequal to the actual mains voltage (U
L
), correct
the calculated current with the ratio between these
voltages, see the following formula:
I
FC . L
= 1 . 1 × I
M, N
× cos φ ×
U
M, N
U
L
The selected VLT
®
Advanced Harmonic Filter AHF 005/AHF
010 must have a nominal current (I
AHF,N
)
≥
the calculated
frequency converter mains input current (I
FC,L
).
NOTICE
Do not oversize the AHF. The best harmonic performance
is obtained at nominal filter load. Using an oversized
filter most likely results in reduced THDi performance.
If connecting several frequency converters to the same
filter, size the AHF according to the sum of the calculated
mains input currents.
NOTICE
If the AHF is sized for a specific load, and the motor is
changed, recalculate the current to avoid overloading
the AHF.
5.1.2 Calculation Example
System mains voltage (U
L
):
380 V
Motor nameplate power (P
M
):
55 kW (75 hp)
Motor efficiency (
ƞ
M
):
0.96
Frequency converter efficiency (
ƞ
FC
):
0.97
AHF efficiency (
ƞ
AHF
)(worst-case estimate):
0.98
Table 5.1 Data for Calculation of Filter Size
Maximum line current (RMS):
P
M
× 1000
U
L
× η
M
× η
FC
× η
AHF
× 3
=
55 × 1000
380 × 0 . 96 × 0 . 97 × 0 . 98 × 3
= 91 . 57 A
In this case, select a 96 A filter.
5.1.3 Voltage Boost
NOTICE
VOLTAGE BOOST
The voltage boost causes the voltage at the frequency
converter terminals to be up to 5% higher than the
voltage at the input of the filter when the capacitors are
not disconnected. Consider this situation when designing
the installation. Take special care in 690 V applications
where the voltage tolerance of the frequency converter
is reduced to +5%, unless a capacitor disconnect is used.
For more information, see
and
.
Selection of Advanced Harmo...
VLT
®
Advanced Harmonic Filter AHF 005/AHF 010
26
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MG80C602
5
5
Summary of Contents for AHF 010
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