Danfoss VLT Refrigeration Drive FC 103 Design Manual page 48

System Integration
total voltage distortion (THD) is calculated based on the
individual voltage harmonics using this formula:
2
U + U
5
THD =
3 3
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 total power).
2 IEC/EN 61000-3-12 Equipment 16–75 A and profes-
sional equipment as from 1 kW 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 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
compy 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
S 3 × R × U
SC =
SCE
Actual (typical)
Limit for
R ≥120
sce
Actual (typical)
Limit for
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.
To connect other power sizes to the public supply network,
consult the distribution network operator.
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
46
VLT
2 2
+ ... + U
7 N
U1
) is greater than or equal to:
sce
× I = 3 × 120 × 400 × I
mains equ equ
Individual harmonic current I
I I I
5 7 11
40 20 10
40 25 15
Harmonic current distortion factor (%)
THD
46
48
Danfoss A/S © 08/2015 All rights reserved.
®
Refrigeration Drive FC 103
currents have on the supply system and for the documen-
tation of compliance with relevant regional guidelines: IEEE
519 -1992; G5/4.
3.2.7.4 Effect of Harmonics in a Power
In Illustration 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
Z and feeds a number of loads. The point of common
xfr
coupling where all loads are connected together is PCC2.
Each load is connected through cables that have an
impedance Z
Illustration 3.4 Small Distribution System
/I (%)
n 1
I
13
Harmonic currents drawn by non-linear loads cause
8
distortion of the voltage because of the voltage drop on
10
the impedances of the distribution system. Higher
impedances result in higher levels of voltage distortion.
PWHD
Current distortion relates to apparatus performance and it
45 relates to the individual load. Voltage distortion relates to
system performance. It is not possible to determine the
46
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.
A commonly used term for describing the impedance of a
grid is the short-circuit ratio R
the ratio between the short circuit apparent power of the
sc
supply at the PCC (S
the load (S
S
ce
R =
sce
S
equ
where
S =
sc
Distribution System
, Z , Z .
1 2 3
. This ratio is defined as
sce
) and the rated apparent power of
sc
).
equ
2
U
and
S = U × I
equ equ
Z
supply
MG16G202