Hello. I'm in Japan, where three phase is mostly open-delta. The short story is that there's no real "problem," but more that I just don't understand what's going on. While testing the current draw on a three phase DC transformer welder, I see that L1 is only about two-thirds of the other two legs, which is "normal" for here. Ditto the three-phase air compressor, etc. However, when I test the current draw on two different inverter welders, it shows no current on L1, and a more or less balanced current on L2 and L3... I'm perplexed as to why this is. I went to a friend's shop and tested his feed using an inverter welder of the same brand I had tested at mine, and L1 shows two-thirds of L2 and L3. I have a much larger service contract than he does; much larger lines from the transformers, etc.
The longer part. I tested multiple machines, and all of the inverter machines show no current on L1 at my place. Transformer welders, as well as multiple pieces of gear like air compressors all show L1 as having two-thirds the current of L2 and L3. This is inherent to open-delta 3p. Everything works fine, and I would have never known. It started as just testing a piece of gear to see what it actually draws, and then turned into a runaway train of testing and trying to figure out why the inverters are doing what they're doing. Swapping phases, swapping what panel and breaker power is taken from. Checking for voltage drop, etc. No current on ground. Nothing changes. I was concerned about the rectifiers in the inverters not sharing load, but when testing one machine, a high-end Panasonic TIG welder, it was showing about 35A while at full power (300A output verified) on L2 and L3, which is what it states for maximum draw, so I doubt it's cooking the diodes. I went as far as messaging Panasoinc, as I'm in the market for a couple of new machines. I explained what's happening, and that I was worried about the bridge rectifier and DC bus capacitor. I was hoping for some detailed info, like maybe components are upsized to deal with open-delta imbalance, but their response was pretty much "you'll be alright" LOL!
In short, I'd like to understand why the power seems fine, but the inverter welders at my shop show no current on L1. My best guess is that the impedance is higher on L1 at my place than my friends place, and that's why his inverters draw current on L1, albeit at 2/3 of L2 and L3.
Thank you for your time.
The longer part. I tested multiple machines, and all of the inverter machines show no current on L1 at my place. Transformer welders, as well as multiple pieces of gear like air compressors all show L1 as having two-thirds the current of L2 and L3. This is inherent to open-delta 3p. Everything works fine, and I would have never known. It started as just testing a piece of gear to see what it actually draws, and then turned into a runaway train of testing and trying to figure out why the inverters are doing what they're doing. Swapping phases, swapping what panel and breaker power is taken from. Checking for voltage drop, etc. No current on ground. Nothing changes. I was concerned about the rectifiers in the inverters not sharing load, but when testing one machine, a high-end Panasonic TIG welder, it was showing about 35A while at full power (300A output verified) on L2 and L3, which is what it states for maximum draw, so I doubt it's cooking the diodes. I went as far as messaging Panasoinc, as I'm in the market for a couple of new machines. I explained what's happening, and that I was worried about the bridge rectifier and DC bus capacitor. I was hoping for some detailed info, like maybe components are upsized to deal with open-delta imbalance, but their response was pretty much "you'll be alright" LOL!
In short, I'd like to understand why the power seems fine, but the inverter welders at my shop show no current on L1. My best guess is that the impedance is higher on L1 at my place than my friends place, and that's why his inverters draw current on L1, albeit at 2/3 of L2 and L3.
Thank you for your time.
