transformer feeding DC drives.

[reyamkram]

I was told by our electrical contractor for the installation of are machines, you can not bound a GEC to a transformer when the when the machine has DC drives.
the transformer feeds the 480 power to the main disconnect of the machine. does any body have any insight in this matter.

Thank you, for any and all information.

 

[zbang]

Any time someone tells me not to bond something, I get suspicious.....

Please tell us a lot more about the installation. What are the transformer connections? What is the machine? By "DC drives", do you mean AC/DC converters feeding DC motors or variable freq. drives feeding AC motors? Or something else?

just guessing here-
some-voltage goes into a transformer with 480v out (wye connected?)
the transformer itself needs to be bonded as an SDS, so to the case, GES, etc. Could be a wye centerpoint, could be one leg of a delta connection, etc.
What is the drive? I'm sure it needs to be bonded to a EGC from the transformer secondary disconnect.
How is the transformer secondary protected? A breaker (as disconnect) or a fused disconnect? Is that also the machine disconnect?

 

[Jraef]

I was told by our electrical contractor for the installation of are machines, you can not bound a GEC to a transformer when the when the machine has DC drives.
the transformer feeds the 480 power to the main disconnect of the machine. does any body have any insight in this matter.

Thank you, for any and all information.

Sounds almost OPPOSITE of the truth (assuming because it is 480V, we are talking about 3 phase input).

DC drives (depending on the design) cause varying amounts of distortion and more importantly, common mode noise and line notching. Because of this, you usually need an isolation transformer between the line source and the drive rectifier, referred to as a "Drive Isolation Transformer" (DIT). What makes it different is that it is a 1:1 ratio, i.e. 480 primary, 480/277 secondary. One purpose is to ABSOLUTELY connect the GEC to the X0 terminal of the DIT on the secondary (drive) side, keeping the effects of the drive isolated to the secondary of that transformer instead of getting back into your entire distribution system and causing more problems. In addition, many drives are designed EXPECTING no more than a 277Vvoltage reference to ground, hence the Wye secondary. If that floats, you can damage the drive rectifier components (again, depending on the design).

 

[Besoeker3]

Sounds almost OPPOSITE of the truth (assuming because it is 480V, we are talking about 3 phase input).

DC drives (depending on the design) cause varying amounts of distortion and more importantly, common mode noise and line notching. Because of this, you usually need an isolation transformer between the line source and the drive rectifier, referred to as a "Drive Isolation Transformer" (DIT). What makes it different is that it is a 1:1 ratio, i.e. 480 primary, 480/277 secondary. One purpose is to ABSOLUTELY connect the GEC to the X0 terminal of the DIT on the secondary (drive) side, keeping the effects of the drive isolated to the secondary of that transformer instead of getting back into your entire distribution system and causing more problems. In addition, many drives are designed EXPECTING no more than a 277Vvoltage reference to ground, hence the Wye secondary. If that floats, you can damage the drive rectifier components (again, depending on the design).

I disagree, old fellow. I know that it's quite common over there on your part of the woods. Even for your 1:1 ratio. Yes, we do add more complex ratios like 12-pulse or 24-pulse but other than that we don't need isolation transformers.

 

[reyamkram]

Any time someone tells me not to bond something, I get suspicious.....

Please tell us a lot more about the installation. What are the transformer connections? What is the machine? By "DC drives", do you mean AC/DC converters feeding DC motors or variable freq. drives feeding AC motors? Or something else?

just guessing here-
some-voltage goes into a transformer with 480v out (wye connected?)
the transformer itself needs to be bonded as an SDS, so to the case, GES, etc. Could be a wye centerpoint, could be one leg of a delta connection, etc.
What is the drive? I'm sure it needs to be bonded to a EGC from the transformer secondary disconnect.
How is the transformer secondary protected? A breaker (as disconnect) or a fused disconnect? Is that also the machine disconnect?

Laminating/ Extrusion machine, one control cabinet is for the extrude and the other is for the control cabinet is for the laminating machine,
the one I am talking about is the laminating machine.
We have a main feed comming from the bus duct to the main disconnect, and that feeds 6-3 phase fuse blocks, and then the fuse blocks feed
6 transformers, ( OLSUN #3989-AD S-48668 ), ( I do believe they are isolation transformers, ) and then the secondary feeds SECO MENTOR 2
DC drives, each trans transformer feeds a different drive.
I am told if they are bonded to GEC, that will blow the drives.
I hope this is enough information. need more please ask.

Thank you,
reyamkram.

 

[zbang]

(More and specific info is always useful.)

I can't find that transformer on the Olsun web site, but I found a couple of Mentor-2 manuals. One pretty clearly says "Drives with isolated heat sinks require that the heat sink is earthed (grounded) for safety."

OTOH, another, possibly newer, manual-
"When possible, remove the (X0) neutral from earth ground to assure that the secondary is isolated from earth ground. Also, corner ground delta-Y connections are discouraged "
Doesn't say don't, says shouldn't.

So, first thing is to get the actual manual for your drive and look at the manufacturer's instructions on grounding.

 

[reyamkram]

(More and specific info is always useful.)

I can't find that transformer on the Olsun web site, but I found a couple of Mentor-2 manuals. One pretty clearly says "Drives with isolated heat sinks require that the heat sink is earthed (grounded) for safety."

OTOH, another, possibly newer, manual-
"When possible, remove the (X0) neutral from earth ground to assure that the secondary is isolated from earth ground. Also, corner ground delta-Y connections are discouraged "
Doesn't say don't, says shouldn't.

So, first thing is to get the actual manual for your drive and look at the manufacturer's instructions on grounding.

Thank you, Form the information, I did E-mail the company about the transformer, and when my supervisor comes in, I will ask about the manuals,
or E-mail the company. I do work nights so I do not get a reply until I come in the next day, I do thank for your help and information.

 

[JoeStillman]

Make sure you understand the difference between EGC (equipment grounding conductor) and GEC (grounding electrode conductor). EGC needs to be bonded to all the non-conducting metal (like the heat sinks). GEC needs to be omitted for the xfmr secondaries. At first glance, this looks like a violation of 250.20(B)(1), but see 250.21(A)(2). Rectifiers for industrial adjustable-speed drives are allowed to float.