Grounding/Bonding Isolation XFMR

[Al Pike]

I have a 480v,1 phase service,with a roto-phase making the 3rd leg for a 50hp pump and well house. Money issue. Its believed the POCO had a spike and it blew out the VFD in the pump control panel. Solution was to install a outdoor isolation xfmr to help protect the drive and to regulate the 490/508v incoming power.

Here's the deal,out of a transfer switch I tapped one set of 1ph w/grn 480vfeeders to the building no neutral,which feeds a OCPD. The other tap is a 3phase 480v set w/grn to the isolation xfmr,which feeds a VFD control panel.The OCPD panel bonds the building water and structure.

I grounded the xfmr case with the EG and the 1-line shows the XO going to the VFD control panel ground bar.There's no neutral.

Now I believe I have to bond the XO to the xfmr case,but do I have to run a bond to the 1st service OCPD? or am I wrong all together.

Thanks for any guidance.

 

[gar]

100129-1733 EST

Al:

Someone else will tell you about your grounding.

An ordinary transformer will not regulate voltage. If you want a voltage regulating transformer, then you would be talking about a Sola type transformer and they are not made that large nor would you want to pay for several.

An ordinary transformer will not limit short time large transient normal mode voltages because these won't saturate the core.

A normal transformer with a Faraday shield will greatly reduce common mode transient voltages.

What is a roto-phase? I assume it is a rotary phase converter.

Is the VFD used to drive the main pump motor?

Basically a VFD requires a DC source. Apparently no standard production units in your size are available that connect to a single phase source.

A wild way to solve your problem, maybe not economical, is to provide a full voltage battery for the bus voltage required by the VFD. The VFD diodes could be removed and the capacitors floated across the battery. Obviously using some circuit protection fuses.

Next you build a single phase charger with a large series inductor to smooth out the current load on the single phase line. This should cause much less peak current on the single phase line and tolerate large source voltage transients. Probably also include means to clip large voltage transients.

Basically this system would be designed to keep the bad stuff out of the electronics and provide a stable voltage.

.

 

[erickench]

The system bonding jumper could be located anywhere from the transformer to the disconnect i.e. OCPD. If the SBJ is located at the disconnect then there must be a bonding jumper from the disconnect enclosure to the transformer casing sized using NEC Table 250.66.

 

[Al Pike]

Yes the VFD is controling the pump motor,and I have installed a SOLA HD 93kVA xfmr.I did'nt design this nightmare Im only installing what the engineer designed.I still think they are going to have problems.Thanks for your help.

 

[erickench]

If the system bonding jumper is installed at the transformer then a bonding jumper sized according to NEC Table 250.122 is installed between the disconnect enclosure and the transformer casing.