A question has come up about the manufacturing machines that we use. Please forgive me if I get some terminology wrong here.
We have many different sizes of machine that are all configured similarly, just with transformers of different sizes. The machine that I have available for testing of the issue has a transformer whose nameplate shows 20 kVA, 230/460 delta primary, 230Y/133 secondary. Those specs are letter for letter taken from the nameplate. The transformer does have a secondary neutral lug, XO. Most of our machines have a transformer that has a delta primary but also a delta secondary. Not sure why this particular one is different.
The machines are fed three phase 480 volt power, which is transformed to 240 via the above mentioned transformer. The resultant 240 is used to power VFDs on some of the motors. Other motors are operating at 480 through motor starters.
The electrical schematic does not show that the transformers neutral lug should be bonded to ground, at best I would call that part of the schematic ambiguous. I called the manufacturer, asking what their intent was and they could not answer me, at least not yet.
Most of the machines if this type that I have seen do not have the neutral bond. I would call this a floating or isolated neutral configuration. Would this configuration not lead lead to the OCPD tripping only when a second secondary conductor is shorted to ground but not the first? Basically an unintentional grounded delta would be created when the first conductor is grounded, correct?
I feel that this is an unsafe situation but I'm not sure how to go about explaining myself. If I am correct, does this configuration present a danger? And if so, could someone point me to resources that explain that danger? My Google skills seem to be letting me down in this one.
We have many different sizes of machine that are all configured similarly, just with transformers of different sizes. The machine that I have available for testing of the issue has a transformer whose nameplate shows 20 kVA, 230/460 delta primary, 230Y/133 secondary. Those specs are letter for letter taken from the nameplate. The transformer does have a secondary neutral lug, XO. Most of our machines have a transformer that has a delta primary but also a delta secondary. Not sure why this particular one is different.
The machines are fed three phase 480 volt power, which is transformed to 240 via the above mentioned transformer. The resultant 240 is used to power VFDs on some of the motors. Other motors are operating at 480 through motor starters.
The electrical schematic does not show that the transformers neutral lug should be bonded to ground, at best I would call that part of the schematic ambiguous. I called the manufacturer, asking what their intent was and they could not answer me, at least not yet.
Most of the machines if this type that I have seen do not have the neutral bond. I would call this a floating or isolated neutral configuration. Would this configuration not lead lead to the OCPD tripping only when a second secondary conductor is shorted to ground but not the first? Basically an unintentional grounded delta would be created when the first conductor is grounded, correct?
I feel that this is an unsafe situation but I'm not sure how to go about explaining myself. If I am correct, does this configuration present a danger? And if so, could someone point me to resources that explain that danger? My Google skills seem to be letting me down in this one.
