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2.9.3 General Aspects of Harmonics

Emission

A frequency converter takes up a non-sinusoidal current

from mains, which increases the input current I

RMS

. A non-

sinusoidal current is transformed with a Fourier analysis

and split into sine-wave currents with different frequencies,

that is, different harmonic currents I

with 50 Hz basic

frequency:

Hz 50 250 350

Table 2.20 Harmonic Currents

The harmonics do not affect the power consumption

directly, but increase the heat losses in the installation

(transformer, cables). So, 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.

175HA034.10

Illustration 2.33 Harmonic Currents

NOTICE

Some of the harmonic currents might disturb communi-

cation equipment connected to the same transformer or

cause resonance with power-factor correction batteries.

To ensure low harmonic currents, the frequency converter

is equipped with intermediate circuit coils as standard. This

normally reduces the input current I

RMS

by 40%.

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 based on the

individual voltage harmonics using this formula:

THD

% =

+ ... +

% of U)

2.9.4

Harmonics Emission Requirements

Equipment connected to the public supply network

Options Definition

1 IEC/EN 61000-3-2 Class A for 3-phase balanced

equipment (for professional equipment only up to 1

kW total power).

2 IEC/EN 61000-3-12 Equipment 16 A-75 A and profes-

sional equipment as from 1 kW up to 16 A phase

current.

Table 2.21 Connected Equipment

2.9.5

Harmonics Test Results (Emission)

Power sizes up to PK75 in T2 and T4 comply with IEC/EN

61000-3-2 Class A. Power sizes from P1K1 and up to P18K

in T2 and up to P90K in T4 comply with IEC/EN

61000-3-12, Table 4. Power sizes P110 - P450 in T4 also

comply with IEC/EN 61000-3-12 even though not required

because currents are above 75 A.

Individual harmonic current I

(%)

Actual

(typical)

40 20 10 8

Limit for

sce

≥120

40 25 15 10

Harmonic current distortion factor (%)

THD PWHD

Actual

(typical)

46 45

Limit for

sce

≥120

48 46

Table 2.22 Harmonics Test Results (Emission)

If the short-circuit power of the supply S

is greater than

or equal to:

= 3 ×

SCE

mains

equ

= 3 × 120 × 400 ×

equ

at the interface point between the user’s supply and the

public system (R

sce

It is the responsibility of the installer or user of the

equipment to ensure that the equipment is connected

only to a supply with a short-circuit power S

greater than

or equal to what is specified above. If necessary, consult

the distribution network operator.

Other power sizes can be connected to the public supply

network by consultation with the distribution network

operator.

Compliance with various system level guidelines:

The harmonic current data in Table 2.22 are given in

accordance with IEC/EN61000-3-12 with reference to the

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