thingstodo
Member
My 2 cents ..
Of course check the grounding of the cables as suggested.
If you check a signal from the pressure sensor (one of them) with a scope (a spectrum analyzer would be better) and determine what your noise frequency is, that is a start.
The noise from the front end of the drives, through the diode bridges, is line frequency * 3, 3 phases. If your noise is at about 180 Hz, the suggested EMI filter on the front end is likely a good solution.
The 350 HP drives likely default to 500 Hz switching frequency. But you should check. Whatever the switching frequency is, if that is where your noise is, changing to 5 KHz or some other available number should make a big difference. The motors will heat up a bit more, and so will the drives. But at the loads you are talking about, the drives won't care. If the sensors are happier with that, you`re done.
The DC Reactors are on the DC bus and need to stay.
If the noise is lower, like 60 Hz, someone could have replaced an instrument power supply with a crappy one and it could be letting 60 Hz noise through. Replacing the instrument power supply is quick and pretty easy. Make sure that the instrument grounds or shields are connected, one side only, to a good bus as suggested already,
If your noise is not either of those, 180 Hz or 500 Hz (or whatever the switching frequency of the drives are), but some other frequency or perhaps a combination of frequencies, it sort of depends on how much money you would like to throw at the problem.
A DV/DT filter (replacing the load reactor) will reduce the spikes and should reduce the 'volume' of the noise. Sized for full load amps fo all 4 motors combined. But it will still be there. And the filter will heat up the VFD cabinet.
A sine wave filter, sized for the full load amps of each motor, installed after the overload for each motor, should get rid of more of the noise. Reducing the `volume`at least, but it should also get rid of some of the higher frequencies entirely. But it is an expensive solution and will heat up the cabinet. Will it be enough? I don't know.
I have no input to give on how much to spend when filtering the VFDs versus filtering the sensors. I don`t have experience with filtering sensors
Of course check the grounding of the cables as suggested.
If you check a signal from the pressure sensor (one of them) with a scope (a spectrum analyzer would be better) and determine what your noise frequency is, that is a start.
The noise from the front end of the drives, through the diode bridges, is line frequency * 3, 3 phases. If your noise is at about 180 Hz, the suggested EMI filter on the front end is likely a good solution.
The 350 HP drives likely default to 500 Hz switching frequency. But you should check. Whatever the switching frequency is, if that is where your noise is, changing to 5 KHz or some other available number should make a big difference. The motors will heat up a bit more, and so will the drives. But at the loads you are talking about, the drives won't care. If the sensors are happier with that, you`re done.
The DC Reactors are on the DC bus and need to stay.
If the noise is lower, like 60 Hz, someone could have replaced an instrument power supply with a crappy one and it could be letting 60 Hz noise through. Replacing the instrument power supply is quick and pretty easy. Make sure that the instrument grounds or shields are connected, one side only, to a good bus as suggested already,
If your noise is not either of those, 180 Hz or 500 Hz (or whatever the switching frequency of the drives are), but some other frequency or perhaps a combination of frequencies, it sort of depends on how much money you would like to throw at the problem.
A DV/DT filter (replacing the load reactor) will reduce the spikes and should reduce the 'volume' of the noise. Sized for full load amps fo all 4 motors combined. But it will still be there. And the filter will heat up the VFD cabinet.
A sine wave filter, sized for the full load amps of each motor, installed after the overload for each motor, should get rid of more of the noise. Reducing the `volume`at least, but it should also get rid of some of the higher frequencies entirely. But it is an expensive solution and will heat up the cabinet. Will it be enough? I don't know.
I have no input to give on how much to spend when filtering the VFDs versus filtering the sensors. I don`t have experience with filtering sensors