What does "Break Frequency" for a VFD mean?
What does "Break Frequency" for a VFD mean?
(OP)
I have an ABB ACS800 vfd and have a question about a parameter in group 30. It is the break point or break frequency. I have seen the same parameters in other drives also. I cannot seem to get a meaningful explanation of what exactly this means. Can anyone break it down in simple terms?
Thanks.
Thanks.





RE: What does "Break Frequency" for a VFD mean?
The -3 dB point (or frequency) is a simplified description of a first order system, usually a low pass system and tells where the Bode diagram is 3 dB down from DC or low frequency gain. Above that frequrncy, the Bode diagram has 'unit slope'. That means that gain decreases 20 dB per decade. Or, in other words, gain is inversely proportional to frequency.
The phase shift is -45 degrees at the break frequency.
It may be a gross simplification to model a servo system as a first order low pass. OTOH, it works quite well as long as there are no other poles or zeros close to (or below) the break frequency.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: What does "Break Frequency" for a VFD mean?
Keith Cress
kcress - http://www.flaminsystems.com
RE: What does "Break Frequency" for a VFD mean?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: What does "Break Frequency" for a VFD mean?
Thanks.
Keith Cress
kcress - http://www.flaminsystems.com
RE: What does "Break Frequency" for a VFD mean?
There is a simple relation between the two, break frequency (f0) = 1/(time constant*two*PI)
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: What does "Break Frequency" for a VFD mean?
Or, in other words, it is part of a set of four parameters that build a custom thermal overload curve for a motor.
Note in the Instruction Manual diagrams about overload curves that Break Frequency is the point where the curve changes from flat (horizontal) to sloping.
It has nothing to do with filters or frequency response in this context.
RE: What does "Break Frequency" for a VFD mean?
I think that the term break frequency should be reserved for its original purpose.
As the OP said, he has seen it in other contexts and I cannot imagine that it is used to describe how thermal protection behaves in other texts.
I think that it is one of the more and more common 'finglish' translation problems that one can find in ABB manuals produced in Finland. I keep a list of some quite funny, but potentially dangerous translations. And it is growing.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: What does "Break Frequency" for a VFD mean?
RE: What does "Break Frequency" for a VFD mean?
RE: What does "Break Frequency" for a VFD mean?
The jury is in... You must read your particular VFD's manual!
Keith Cress
kcress - http://www.flaminsystems.com
RE: What does "Break Frequency" for a VFD mean?
RE: What does "Break Frequency" for a VFD mean?
RE: What does "Break Frequency" for a VFD mean?