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Tuned Filter for Specific Mains Voltage Frequency

Tuned Filter for Specific Mains Voltage Frequency

Tuned Filter for Specific Mains Voltage Frequency

(OP)
Help, We are trying to filter out a switching frequency (used to switch street lighting and control domestic hot water), we have some electronic lighting dimmers (echelon network based) that are being affected by the previously mentioned "ripple" frequency (the lights they control are flickering enough to make it look like a sub standard installation). The "ripple" frequency is meant to be 1050Hz I understand, and it is superimposed on the mains frequency of 50Hz. the problem is that the method of generation in this locality is via an old motor generator, which we understands slips and is inconsistent in it's generated frequency (it works fine for switching frequency relays). the end result is the flickering light. is it possible to fit some sort of filter to prevent this stray band of frequencies effecting our dimmer circuit. Please Help ASAP. Thanks Mike. PS we have tried a capactor but still not right.

RE: Tuned Filter for Specific Mains Voltage Frequency

Suggestions:
1. Motor generator may need a governor or some suitable speed control.
2. Filters can remove harmonics, spikes, etc. but will not correct the frequency changes in the power distribution.
3. An AC-DC-AC converter might be considered. There are plenty of them on the market. AC-DC-AC uninterruptible power supply might also be considered.

RE: Tuned Filter for Specific Mains Voltage Frequency

A 1:1 transformer would probably filter out the ripple voltage because it will appear as a high impedance to the higher frequencies.  It would be expensive for a large service and add losses.  A series reactor would serve the same purpose.

If the utility's method of controlling street lights and load management water heater switches is causing you power quality problems, you should complain to them.  It should be the utility's responsibility to fix the problem, not yours.  If you don't get any satisfaction, contact the regulatory authority.

A capacitor or parallel filter would interfere with the switching function for the whole circuit.  The transformer or a reactor would only block the ripple frequency on your service and would not affect the function on the rest of the circuit.

RE: Tuned Filter for Specific Mains Voltage Frequency

At first some comments to jbartos suggestions:

1. This action alone will not change much
2. This action alone will not change much
3. Will work, but at high cost and the risk of new problems

At first some general comments:

Usually ripple control frequency is choosen to be an non-integral multiple of the supply frequency. 3phasemike, check if the the frequency mentioned in you post are really used (..is meant to be 1050 Hz I understand..).

If your assumption is true, you might get a beat-frequency effect by mixing 50 Hz with slight variations with a fixed 1050 Hz frequency resulting in subharmonics of a few Hz.

There are several ways to avoid the problem:

-Change ripple control frequency slightly to e.g. 1025 Hz. Might be difficult, but thats the common way to operate ripple control systems. Beat frequencies will fall outside the flicker range from 0,1..10Hz

-Synchronise the ripple control frequency to be exactly 21 times the actual mains frequency.

-Combine jbartos suggestions 1 and 2.

All approaches need to make changes two the whole system, but since your problem is a system related problem a viable solution has to go a system approach.

If thats not possible your only chance is to use a series filter that blocks the 1050Hz. This approach will work as long as the 1050 Hz are quite constant. But with this approach similar problems at other loads can be expected for the future.

RE: Tuned Filter for Specific Mains Voltage Frequency

(OP)
Thanks all for you suggestions, since posting this I have further information. The local authorities method of generation is via an 3 phase induction motor, this has, by its nature an a mount of slippage, resulting in a generated frequency of "about 1042Hz", the resultant beat frequency causes our dimmers to flicker when this frequency is being injected onto the lines. We have spoken to several local companies and the first "cheep" option is to look at installing a capacitive circuit prior to the dimmers, the required capacitance is around 160 microF, this will draw approx. 11A from the mains (apparently it won't show up in the power bill due to the nature of the power) it will require the capacitors to be installed in a metal box for fire protection and a circuit breaker to minimise overload faults. the effect on the dimmer circuits can not be commented on though without R+D. the local authority aren’t so keen on this as it acts as a "sinking" circuit muffling the frequencies close to the dimmer and causing them to have to generate a more. they prefer us to use a "blocking" circuit this a tuned inductive and capactive circuit to filter out only the ripple frequency causing the problem, it will require. it will require more cost and R+D, again there is no way to predict if it will work or it's effect on the dimmers. I await your feedback, Thanks Mike

RE: Tuned Filter for Specific Mains Voltage Frequency

If you are pursuing the filter option, consider constructing the filter as a resonant L-C circuit ('tank circuit') connected in series with your supply. This will have low impedance to your supply frequency and will reject the troublesome frequency, rather than attempt to sink it into a parallel filter.
This option may prove expensive as power levels escalate, as the filter must carry your full load current. Economics probably depend on relative power levels of your load and the source of the interfering signal - a powerful source may be able to sink a lot of current into a parallel filter which then also becomes expensive.

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