•
Class 3 relates to compatibility levels greater than the public supply network. This class applies only to IPCs in
industrial environments. Use this class where the following equipment is found:
-
Large converters.
-
Welding machines.
-
Large motors starting frequently.
-
Loads that change quickly.
Typically, a class cannot be defined ahead of time without taking into account the intended equipment and processes to be
used in the environment. VLT
®
AutomationDrive FC 302 Low Harmonic Drive observes the limits of Class 3 under typical
supply system conditions (R
SC
>10 or
Vk Line
<10%).
Harmonic order (h)
Class 1 (V
h
%)
Class 2 (V
h
%)
Class 3 (V
h
%)
5
3
6
8
7
3
5
7
11
3
3.5
5
13
3
3
4.5
17
2
2
4
17
˂
h≤49
2.27 x (17/h) – 0.27
2.27 x (17/h) – 0.27
4.5 x (17/h) – 0.5
Table 1.7 Compatibility Levels for Harmonics
Class 1
Class 2
Class 3
THD(V)
5%
8%
10%
Table 1.8 Compatibility Levels for the Total Harmonic Voltage Distortion THD(V)
1.6.5 IEEE Harmonic Standards
The IEEE 519 standard (Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems)
provides specific limits for harmonic voltages and currents for individual components within the supply network. The
standard also provides limits for the sum of all loads at the point of common coupling (PCC).
To determine permissible harmonic voltage levels, IEEE 519 uses a ratio between the supply short-circuit current and the
maximum current of the individual load. For permissible harmonic voltage levels for individual loads, see
. For
permissible levels for all loads connected to the PCC, see
.
I
SC
/I
L
(R
SCE
)
Permissible individual harmonic voltages
Typical areas
10
2.5–3%
Weak grid
20
2.0–2.5%
1–2 large loads
50
1.0–1.5%
A few high-output loads
100
0.5–1%
5–20 medium-output loads
1000
0.05–0.1%
Strong grid
Table 1.9 Permissible Voltage THD at the PCC for Each Individual Load
Voltage at the PCC
Permissible individual harmonic voltages
Permissible THD(V)
V
Line
≤69 kV
3%
5%
Table 1.10 Permissible Voltage THD at the PCC for all Loads
Limit harmonic currents to specified levels, as shown in
. IEEE 519 utilises a ratio between the supply short-circuit
current and the maximum current consumption at the PCC, averaged over 15 minutes or 30 minutes. In certain instances
Introduction
VLT
®
AutomationDrive FC 302 Low Harmonic Drive
132–630 kW
18
Danfoss A/S © Rev. 04/2015 All rights reserved.
MG37A322
1
1
