GE AF-600 FP Design Manual page 38

2.9.4 General Aspects of Harmonics Emission
A frequency converter takes up a non-sinusoidal current from mains, which
increases the input current I . A non-sinusoidal current is transformed by
RMS
means of a Fourier analysis and split up into sine-wave currents with different
frequencies, i.e. different harmonic currents I
quency:
The harmonics do not affect the power consumption directly but increase the
heat losses in the installation (transformer, cables). Consequently, in plants
with a high percentage of rectifier load, maintain harmonic currents at a low
level to avoid overload of the transformer and high temperature in the cables.
NB!
Some of the harmonic currents might disturb communication equipment connected to the same transformer or cause resonance in connection with power-
factor correction batteries.
NB!
To ensure low harmonic currents, the frequency converter is equipped with intermediate circuit coils as standard. This normally reduces the input current I
by 40%.
RMS
The voltage distortion on the mains supply voltage depends on the size of the harmonic currents multiplied by the mains impedance for the frequency in question.
The total voltage distortion THD is calculated on the basis of the individual voltage harmonics using this formula:
2 2
THD % = U + U + ... + U
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2.9.5 Harmonics Emission Requirements
Equipment connected to the public supply network:
2.9.6 Harmonics Test Results (Emission)
Power sizes from 0.75 kW and up to 18.5 kW in 200 V and up to 90 kW in 460 V complies with IEC/EN 61000-3-12, Table 4. Power sizes 110 - 450 kW in 460 V also
complies with IEC/EN 61000-3-12 even though not required because currents are above 75 A.
Provided that the short-circuit power of the supply S
S SC R SCE U mains
= 3 × × ×
at the interface point between the user's supply and the public system (R
It is the responsibility of the installer or user of the equipment to ensure, by consultation with the distribution network operator if necessary, that the equipment
is connected only to a supply with a short-circuit power S
Other power sizes can be connected to the public supply network by consultation with the distribution network operator.
with 50 Hz as the basic fre-
N
2
N
is greater than or equal to:
sc
I equ I equ
= 3 × 120 × 400 ×
).
sce
greater than or equal to specified above.
sc
Harmonic currents I
1
Hz 50 Hz
(U % of U)
N
Options: Definition:
1 IEC/EN 61000-3-2 Class A for 3-phase balanced equip-
ment (for professional equipment only up to 1 kW total
power).
2 IEC/EN 61000-3-12 Equipment 16A-75A and professional
equipment as from 1 kW up to 16A phase current.
AF-600 FP Design Guide
I I
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250 Hz 350 Hz
2
37