Ground Leakage Current; Mg20N622; Danfoss A/S © 09/2014 All Rights Reserved - Danfoss VLT AQUA Drive FC 202 Design Manual

System Integration
A commonly used term for describing the impedance of a
grid is the short-circuit ratio R
between the short circuit apparent power of the supply at
the PCC (S ) and the rated apparent power of the load
sc
3 3
(S ).
equ
S
ce
R =
sce
S
equ
where
S =
sc
Z
The negative effect of harmonics is two-fold
•
Harmonic currents contribute to system losses (in
cabling, transformer).
•
Harmonic voltage distortion causes disturbance
to other loads and increase losses in other loads.
Non-linear
Current
Contribution to
system losses
Figure 3.5 Negative Effects of Harmonics
3.2.7.5 Harmonic Limitation Standards and
Requirements
The requirements for harmonic limitation can be:
•
Application-specific requirements.
•
Standards that must be observed.
The application-specific requirements are related to a
specific installation where there are technical reasons for
limiting the harmonics.
Example
A 250 kVA transformer with two 110 kW (150 hp) motors
connected is sufficient if one of the motors is connected
directly online and the other is supplied through an
adjustable frequency drive. However, the transformer is
undersized if both motors are supplied by the adjustable
frequency drive. Using additional means of harmonic
reduction within the installation or selecting low harmonic
drive variants makes it possible for both motors to run
with adjustable frequency drives.
There are various harmonic mitigation standards,
regulations, and recommendations. Different standards
apply in different geographical areas and industries. The
following standards are the most common:
52
, defined as the ratio
sce
2
U
and
S = U × I
equ equ
supply
System
Impedance
Danfoss A/S © 09/2014 All rights reserved.
®
VLT AQUA Drive FC 202
•
•
•
•
•
See the AHF 005/010 Design Guide for specific details on
each standard.
In Europe, the maximum THVD is 8% if the plant is
connected via the public grid. If the plant has its own
transformer, the limit is 10% THVD. The VLT
designed to withstand 10% THVD.
3.2.7.6 Harmonic Mitigation
In cases where additional harmonic suppression is
required, Danfoss offers a wide range of mitigation
equipment. These are:
Voltage
•
•
•
Disturbance to
other users
•
The choice of the right solution depends on several
factors:
•
•
•
•
Always consider harmonic mitigation if the transformer
load has a non-linear contribution of 40% or more.
Danfoss offers tools for calculation of harmonics, see
chapter 2.8.2 PC Software.

3.2.8 Ground Leakage Current

Follow national and local codes regarding protective
grounding of equipment where leakage current exceeds
3.5 mA.
Adjustable frequency drive technology implies high
frequency switching at high power. This generates a
leakage current in the ground connection.
IEC61000-3-2
IEC61000-3-12
IEC61000-3-4
IEEE 519
G5/4
12-pulse drives
AHF filters
Low Harmonic Drives
Active Filters
The grid (background distortion, line power
unbalance, resonance and type of supply
(transformer/generator).
Application (load profile, number of loads and
load size).
Local/national requirements/regulations (IEEE519,
IEC, G5/4, etc.).
Total cost of ownership (initial cost, efficiency,
maintenance, etc.).
®
AQUA Drive is

MG20N622