Danfoss VLT AHF005, Design Manual

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direct on-line motor should also be supplied through a
frequency converter the transformer will, in this case, be
undersized. In order to retrofit, without changing the
transformer, the harmonic distortion from the two frequency
converterhas to be mitigated using AHF filters.
There are various harmonic mitigation standards, regulations
and recommendations. Different standards apply in different
geographical areas and industries. The following
encountered standards will be presented:
•
IEC/EN 61000-3-2
•
IEC/EN 61000-3-12
•
IEC/EN 61000-3-4
•
IEC 61000-2-2
•
IEC61000-2-4
•
IEEE 519
•
G5/4
IEC 61000-3-2, Limits for harmonic current emissions
(equipment input current
≤
16A per phase)
The scope of IEC 61000-3-2 is equipment connected to the
public low-voltage distribution system having an input
current up to and including 16 A per phase. Four emission
classes are defined: Class A through D. The Danfoss
frequency converters are in Class A. However, there are no
limits for professional equipment with a total rated power
greater than 1kW.
IEC 61000-3-12, Limits for harmonic currents produced by
equipment connected to public low-voltage systems with
input current >16A and
≤
75A
The scope of IEC 61000-3-12 is equipment connected to the
public low-voltage distribution system having an input
current between 16A and 75A. The emission limits are
currently only for 230/400V 50Hz systems and limits for other
systems will be added in the future. The emission limits that
apply for drives are given in Table 4 in the standard. There
are requirements for individual harmonics (5th, 7th, 11th,
and 13th) and for THD and PWHD. Frequency converters
from the Automation Drive series (FC 102 HVAC, FC 202
Aqua and FC 302 Industry) comply with these limits without
additional filtering.
IEC 61000-3-4, Limits, Limitation of emission of harmonic
currents in low-voltage power supply systems for equipment
with rated current greater than 16A
IEC 61000-3-12 supersedes IEC 61000-3-4 for currents up to
75A. Therefore the scope of IEC 61000-3-4 is equipment with
rated current greater than 75A connected to the public low-
voltage distribution system. It has the status of
Technical
report and should not be seen as an international standard. A
three-stage assessment procedure is described for the
connection of equipment to the public supply and
equipment above 75A is limited to stage 3
connection based
on the load's agreed power . The supply authority may accept
the connection of the equipment on the basis of the agreed
active power of the load's installation and local requirements
of the power supply authority apply. The manufacturer shall
provide individual harmonics and the values for THD and
PWHD.
IEC 61000-2-2 and IEC 61000-2-4 Compatibility levels for low-
frequency conducted disturbances
IEC 61000-2-2 and IEC 61000-2-4 are standards that stipulate
compatibility levels for low-frequency conducted distur-
bances in public low-voltage supply systems (IEC 61000-2-2)
and industrial plants (IEC 61000-2-4). These low-frequency
disturbances include but are not limited to harmonics. The
values prescribed in these standards shall be taken into
consideration when planning installations. In some
situations the harmonic compatibility levels can not be
observed in installations with frequency converters and
harmonic mitigation is needed.
IEEE519, IEEE recommended practices and requirements for
harmonic control in electrical power systems
IEEE519 establishes goals for the design of electrical systems
that include both linear and nonlinear loads. Waveform
distortion goals are established and the interface between
sources and loads is described as point of common coupling
(PCC).
IEEE519 is a system standard that aims the control of the
voltage distortion at the PCC to a THD of 5% and limits the
maximum individual frequency voltage harmonic to 3%. The
development of harmonic current limits aims the limitation
of harmonic injection from individual customers so they will
not cause unacceptable voltage distortion levels and the
limitation of the overall harmonic distortion of the system
voltage supplied by the utility.
The current distortion limits are given in Table 10.3 in the
standard and depend on the ratio I
SC
/I
L
where I
SC
is the short
circuit current at the utility PCC and I
L
is the maximum
demand load current. The limits are given for individual
harmonics up to the 35th and total demand distortion (TDD).
Please note that these limits apply at the PCC to the utility.
While requiring individual loads to comply with these limits
also ensures the compliance at the PCC, this is rarely the
most economic solution, being unnecessarily expensive. The
most effective way to meet the harmonic distortion
requirements is to mitigate at the individual loads and
measure at the PCC.
However, if in a specific application it is required that the
individual drive should comply with the IEEE519 current
distortion limits, an AHF can be employed to meet these
limits.
G5/4, Engineering recommendation, planning levels for
harmonic voltage distortion and the connection of non-
linear equipment to transmission systems and distribution
networks in the United Kingdom
G5/4 sets planning levels for harmonic voltage distortion to
be used in the process of connecting non-linear equipment.
A process for establishing individual customer emission
Introduction to Harmonics a... AHF005/010 Design Guide
10 MG.80.C4.02 - VLT
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