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Illustration 4.34 Summation CTs on generator backup
applications (PCC-side). Filter compensates full current of
transformer and generator.
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Illustration 4.35 Summation CTs example for individual harmonic
compensation (load side).
Summation current transformers are available with
multiple (2-5) inputs and common output. For application
where summations CTs are used to add current from
several sources make sure that all CTs connected to the
summation are from the same manufacturer and that the
CT have:
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same polarity
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same primary rate
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same RMS value
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same accuracy (class 0.5)
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same location (PCC or load-side)
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same phase sequence
NOTE
Use summation CT with great caution and always insure
correct phase sequence, current direction, primary and
secondary rate. If installation is incorrect the filter will not
work according to expectations.
The current transformers burden calculation has to include
all wires in the installation and must be conducted for the
longest total wire string when using summation CTs.
4.5.10 Active Filter Operating with
Capacitor Banks
The VLT Active Filter is able to run in conjunction with
capacitor banks as long as the resonance frequency of the
capacitor bank is not in the operation range of the Active
Filter.
NOTE
Always use detuned capacitor banks in installation with
frequency converter and active filters to avoid resonance
phenomena, unintended tripping or even component
brake down.
For the case of detuned capacitors, the resonance
frequency capacitors should be tuned for an inter-
harmonic number lower than the 3rd harmonic. The VLT
Active Filter has to operate in selective compensation
mode if filter is installed in conjunction with capacitor
banks of any kind.
Capacitor bank should ideally be installed upstream of the
filter / towards the transformer. If not possible the current
transformers should be installed in a way that they do not
measure both needed current compensation and the
capacitor corrected current.
How to Install
VLT Active Filter AAF 00x
32
MG.90.V2.02 - VLT® is a registered Danfoss trademark
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