Danfoss VLT AQUA Drive FC 202 Design Manual page 53

System Integration
The voltage distortion on the line power supply voltage
depends on the size of the harmonic currents multiplied
by the line power 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 2
U + U + ... + U
5 7 N
THD =
U1
3.2.7.2 Harmonics Emission Requirements
Equipment connected to the public supply network
Option Definition
1 IEC/EN 61000-3-2 Class A for 3-phase balanced
equipment (for professional equipment only up to 1
kW (1.4 hp) total power).
2 IEC/EN 61000-3-12 Equipment 16 A-75 A and profes-
sional equipment as from 1 kW (1.4 hp) up to 16 A
phase current.
Table 3.12 Harmonics Emission Standards
3.2.7.3 Harmonics Test Results (Emission)
Power sizes up to PK75 in T2 and T4 complies with IEC/EN
61000-3-2 Class A. Power sizes from P1K1 and up to P18K
in T2 and up to P90K in T4 complies with IEC/EN
61000-3-12, Table 4. Power sizes P110–P450 in T4 also
complies with IEC/EN 61000-3-12 even though not required
because currents are above 75 A.
Table 3.13 describes that the short-circuit power of the
supply S at the interface point between the user's supply
sc
and the public system (R ) is greater than or equal to:
sce
S 3 × R × U × I = 3 × 120 × 400 × I
SC =
SCE line power equ
Individual harmonic current I
I
5
Actual (typical) 40
Limit for
40
R ≥120
sce
Harmonic current distortion factor (%)
THD
Actual (typical) 46
Limit for
48
R ≥120
sce
Table 3.13 Harmonics Test Results (Emission)
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
greater than or equal to that specified in the equation.
MG20N622
Design Guide
equ
/I (%)
n 1
I I I
7 11 13
20 10 8
25 15 10
PWHD
45
46
sc
Danfoss A/S © 09/2014 All rights reserved.
Consult the distribution network operator to connect other
power sizes to the public supply network.
Compliance with various system level guidelines:
The harmonic current data in Table 3.13 are provided in
accordance with IEC/EN61000-3-12 with reference to the
power drive systems product standard. They may be used
as the basis for calculation of the influence harmonic
currents have on the power supply system and for the
documentation of compliance with relevant regional
guidelines: IEEE 519 -1992; G5/4.
3.2.7.4 Effect of Harmonics in a Power
Distribution System
In Figure 3.4, a transformer is connected on the primary
side to a point of common coupling PCC1, on the medium
voltage supply. The transformer has an impedance of Z
and feeds a number of loads. The point of common
coupling where all loads are connected together is PCC2.
Each load is connected through cables that have an
impedance of Z , Z , Z .
1 2 3
Figure 3.4 Small Distribution System
Harmonic currents drawn by non-linear loads cause
distortion of the voltage because of the voltage drop in
the impedances of the distribution system. Higher
impedances result in higher levels of voltage distortion.
Current distortion relates to apparatus performance, which
in turn relates to the individual load. Voltage distortion
relates to system performance. It is not possible to
determine the voltage distortion in the PCC knowing only
the load's harmonic performance. To predict the distortion
in the PCC, the configuration of the distribution system
and relevant impedances must be known.
3 3
xfr
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