Harmonic Filters

How does a filter 'trip'?

One might expect a circuit breaker to trip on overcurrent, but a filter?

Methinks we need a more fulsome desription of the problem if any meaningful answers are to be given.

Maybe it's clogged and needs to be changed, or cleaned.

OK, OK.

Just stirring things.

the capacitors of the filter are connected to bus through circuit breaker ,which trips. again my question is ,when the filter is designed ,the worst operation of furnace is kept in mind.if I have 250Hz filter , it should supress all 250Hz frequency , irrespective of the amount/severity of 250Hz harmonic. Is it correct?

An ideal notch filter should cut off a specific frequency (or a specific frequency range in the case of a band-reject filter) completely, no matter how large the input signal's amplitude is. However, in practice, any filter has a specific (large but finite) attenuation (e.g. 50db). So if the input signal is really large a small but significant amount will pass on the filter's output. So, when you design a filter you should take into consideration the larger possible input signal (worst case) and the maximum accepted output signal, in order to find out the (minimum) attenuation that your filter should have.

It depends on the magnitude of the disruptive current created by the harmonic.

If the filter is not sized large enough to handle/dissipate the generated harmonic current by the application it will not operate correctly.

There could also be a failed or inferior component of the filter assembly that is causing the issue.

If this is a factory designed and supplied filter assembly; you would be wise to contact the manufacturer and verify the assembly is the correct one for your application.

If it is the correct unit for your application; I would suggest starting with analyzing the capacitors in the filter for proper microfarad rating/performance and verify all resistors are of the correct impedance.

Take it easy, guys!!

The early transmitters in the 1920s or so, were driven by carbon arc. The arc has an inherently negative portion of its characteristic. It drives the generation of the Radio Frequency for the transmission.

Since it is inherently nonlinear, plenty of harmonics are generated.

SO IS IN A FURNACE. The fellow is correct, so far.

So, the question remains about the design of the filter, before further discussions are sensible.

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50Hz 5th Harmonic 250Hz 7th Harmonic 350Hz Distortion

If a capacitor is faulted, surely this will cause the imbalance on the busbars and cause the trip due to not filtering at the correct frequency.

Well, discuss the matter with the filter manufacturer by telephone, then.

Or is that the 7th harmonic of the bleedin' obvious?

Is it a tuned filter or a de-tuned filter?

There are some filter basics needed to be understood.

1,. They reflect the considerable energy (20-40%) of the harmonics back into the furnace, to better efficiency.

2,. They prevent not permissible high harmonic current on the power grid.

3,. Any filter stage can do only so much dampening / reflection from harmonic to harmonic. Hence multistage filters are normal. A 90% reduction in energy (from the fundamental frequency) to the 3rd per stage is ordinary.

4,. The higher the Q quality of the stage, the higher the filtering. At the same time the voltage or current stresses are multiplied on its components by the same Q multiplier. That sets rather sharp limits on applicable Q.

5,. Components, in particular capacitors need to be protected from excessive currents, hence the OP's mention of the 5th harmonic breaker tripping. That may happen for a reason, all right. But, OP needs to make some measurements with some real test equipment, to know which way to proceed.

Harmonic filters are rather complicated in their construction and behaviour. A breaker on - light on, breaker off - light off approach to troubleshooting is wholly inadequate.

leveles, I made a comment on another question by this poster several days ago, that he should be seeking other help with his issues. Arc furnace control is an art and should be handle by those who know these systems.

Your comments were spot on!