Electricity + Control January 2017

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DRIVES, MOTORS + SWITCHGEAR
take note
harmonics and will, in fact, help reduce them
when they are present
• If there is a mixture of 6 pulse and AFE drives
on the same switchboard, the ripple in voltage
from the AFE drive can raise the dc bus voltage
in the 6 pulse VFDs creating overvoltage condi-
tions
• Although an active solution, AFEs still require input pas-
sive filters (LCL and EMI/RFI filters) to control switching frequency
harmonics and to attenuate ripple in the mains side voltage and
current
• LCL and EMI/RFI filters are more likely to resonate with the power
system at rectifier harmonic frequencies (ie. 5th, 7th, 11th, etc.) than
the Lineator AUHF. Also under lightly loaded conditions, the
reactive power of the LCL capacitors can cause over-excitation
of generators
• AFEs generate significant levels of ground leakage current which
can cause inadvertent ground fault trips and failure of sensitive
equipment
• AFE losses are significantly higher and efficiencies much lower
than a 6 pulse VFD with Lineator AUHF
Figure 5: Efficiency comparison – AFE vs 6-P VSD with lineator.
Conclusion
In conclusion, the criteria for each application need to be taken on
its own merit, in conjunction with the VSD manufacturer, in order to
ensure the correct product supply for your requirements.
Bibliography
[1] Hoevenaars A. Advantages of 6-Pulse VFD with Lineator AUHF
vs Active Front End (AFE) Drives. Mirus International Inc.
Reference
[1] IEEE 519: 1992. Recommended practice and requirements for
harmonic control in electric power systems.
(ANSI/IEEE Standard 519 − Guide for harmonic control and reac-
tive compensation of static power converters − first published in
1981).
Glen Ward was born in South Africa in 1972. Glen has
more than 20 years’ experience with VSDs and associated
products. He completed an N6 diploma and T4 between
1993 and 1995. Thereafter he worked for various contract
electronics companies that operated in the industrial mo-
tion control sector (Variable speed drives). In 2004 Glen
joined Zest Electric Motors as a sales engineer to support the WEG range
of automation products. In 2009 he was promoted to Drives and Automation
manager in the KZN region where he has remained until present. His main
area of interest has been to investigate and highlight areas of efficiency
improvement. Enquiries: Kirsten Larkan. Tel. +27 (0) 11 723 6000 or email
• IEEE 519 was published in 1981.
• IEEE 519 is not a mandatory standard but rather a reference
to specify harmonic distortion limits.
• IEEE 519 was revised in 1992 to provide recommendations
on maximum allowable levels of harmonic current distortion.
Type VSD Rat-
ing (KW)
VSD Losses
(KW)
AUHF Losses
(KW)
Total Losses
(KW)
Efficiency Difference
AFE Drive 6-P
with Lineator
75 4,4 4,1 94,80%
1,9 0..8 2,7 96,50% 1,70%
AFE Drive 6-P
with Lineator
20 < 50
400 20 20 95,20%
9,1 3,6 12,7 96,90% 1,70%
Electricity+Control January ‘17 14