I have a question regarding harmonics mitigation, probably for the engineers in the forum. Sorry about the long story below, question is at the end.
I have been peripherally involved with problem that has occurred at a wastewater treatment plant that has a large UV disinfecting system installed. The system uses banks of UV lamps (basically mercury vapor lamps) with electronic ballasts.
The plant main power is 480V, 3PH, 3W. The UV system requires 277V. A 150KVA UPS with a 480V, 3W input - 480/277V, 4W output feeds the system. There is a by-pass feed with a 225KVA (was 150KVA), 480V - 480/277V xfmr.
The system was up and running for a couple of years, seemly operating OK. Then it recently started having problems. The UPS began tripping off and the system would go into by-pass. This happened often enough that they ended up leaving it in by-pass for some time. Then, the by-pass xfmr (the original 150KVA) started getting very hot (per operations). At some point, operations decided to replace the xfmr with a bigger 225KVA, thinking this would solve the problem. It did reduce the heat, but they still could not seem to get it back on the UPS full time. They contacted my company to have an engineer study the problem.
We had them contract a testing company to monitor the power at the point of connection to the UV system for a month. Most everything was normal, except for the harmonics levels. The phase levels were fairly low, but the neutral harmonics were off the charts. This makes sense as all the load is 277V. This explained the original 150KVA xfmr getting very hot. The original xfmr was not 'K' rated to handle the non-linear load of the ballasts, so the neutral was probably smoking. Although we would have rather they replaced with a 'K' rated xfmr, the new 225KVA seems to be handling it for now.
We still don't know why the UPS system just stopped working, could be something wrong with it. We have had a little trouble getting info from the plant about any changes, upgrades etc to the UV system, due to changes in plant personnel, so there may be something they aren't telling us... who knows.
Now my question: The UV system in question is fed 277V and has huge neutral harmonics. Obviously it comes from the ballasts. Maybe that's the way it is, maybe they are "low quality" ballasts, who knows why.
I recently saw a system that had 240V ballasts fed from a 480V - 240/120V xfmr. There was a neutral, but it only fed aux loads, not the lamps. That means that any harmonics are on the phases.
Seem like this would be a better way to go when dealing with a high non-linear load? Wouldn't that lower the harmonics levels and or make them easier to handle? I'm not sure what the UPS config would be, considering most of these plants have 480V, 3PH, 3W systems.
I have been peripherally involved with problem that has occurred at a wastewater treatment plant that has a large UV disinfecting system installed. The system uses banks of UV lamps (basically mercury vapor lamps) with electronic ballasts.
The plant main power is 480V, 3PH, 3W. The UV system requires 277V. A 150KVA UPS with a 480V, 3W input - 480/277V, 4W output feeds the system. There is a by-pass feed with a 225KVA (was 150KVA), 480V - 480/277V xfmr.
The system was up and running for a couple of years, seemly operating OK. Then it recently started having problems. The UPS began tripping off and the system would go into by-pass. This happened often enough that they ended up leaving it in by-pass for some time. Then, the by-pass xfmr (the original 150KVA) started getting very hot (per operations). At some point, operations decided to replace the xfmr with a bigger 225KVA, thinking this would solve the problem. It did reduce the heat, but they still could not seem to get it back on the UPS full time. They contacted my company to have an engineer study the problem.
We had them contract a testing company to monitor the power at the point of connection to the UV system for a month. Most everything was normal, except for the harmonics levels. The phase levels were fairly low, but the neutral harmonics were off the charts. This makes sense as all the load is 277V. This explained the original 150KVA xfmr getting very hot. The original xfmr was not 'K' rated to handle the non-linear load of the ballasts, so the neutral was probably smoking. Although we would have rather they replaced with a 'K' rated xfmr, the new 225KVA seems to be handling it for now.
We still don't know why the UPS system just stopped working, could be something wrong with it. We have had a little trouble getting info from the plant about any changes, upgrades etc to the UV system, due to changes in plant personnel, so there may be something they aren't telling us... who knows.
Now my question: The UV system in question is fed 277V and has huge neutral harmonics. Obviously it comes from the ballasts. Maybe that's the way it is, maybe they are "low quality" ballasts, who knows why.
I recently saw a system that had 240V ballasts fed from a 480V - 240/120V xfmr. There was a neutral, but it only fed aux loads, not the lamps. That means that any harmonics are on the phases.
Seem like this would be a better way to go when dealing with a high non-linear load? Wouldn't that lower the harmonics levels and or make them easier to handle? I'm not sure what the UPS config would be, considering most of these plants have 480V, 3PH, 3W systems.
