12kW power supply on the end of 300m cable...what to use for chassis ground?

Hi,
We are making an SMPS which will be at the end of a 300m cable.
The Vin is 700VDC. This is from an isolated 700VDC source.
Pout = 12Kw. (48vout)
It will comprise “units” comprising of a vicor BCM module feeding four vicor DCM modules…..and these “units” paralleled in a whopping group of 10 to give the 48V, 12Kw output.
We need to connect the chassis of the BCM modules to chassis ground or earth………also, the App notes state that under each DCM module there must be a copper plane, which is connected to either chassis ground or earth.
The thing is, we don’t have an separate earth wire going to our product, and cant have this.
We will simply be using 700VDC negative as our chassis ground.
Also, we plan to connect the 700VDC negative to Earth…(so as to avoid this isolated output getting induced up to some high voltage).
Do you think these measures are appropriate?

BCM datasheet

https://www.vicorpower.com/documents/datasheets/ds_BCM4414xG0F4440yzz.pdf

DCM datasheet

https://www.vicorpower.com/documents/datasheets/DCM3623x50M53C2yzz_ds.pdf

Also, what must we connect our Y caps to if we only have a “go” and “return” going to the product?...and the chassis ground is our “return”
…Or is it that we should simply just implement common mode EMC protection with a common mode choke only?
The BCM and DCM modules are transformer isolated………so we believe to a considerable extent we can combat common mode noise by simply connecting primary and secondary with shorts……this will short out the transformer stray capacitances from primary to secondary we believe. Would you agree?

Is this question related to this thread by any chance?

Reminds me of a cartoon which I saw around 1970...

An astronaut in all his finery, standing on the moon, holding a wire in his gloved hand.
The caption read:
"Say Houston, what did you say we should do with this wire labelled "Earth" ?"


On a more practical level, you could connect the Y capacitors to the frame of the drone (?).
There may or may not be any benefit in doing that.

Be aware that a 300 metre long cable connected to earth at one end will make an effective standoff insulator at about 250kHz. (Quarter wavelength line).
Makes for a good transmitting antenna at such frequencies.

Also be aware that in the operation manual for this thing, you must highlight the electric shock hazard when the thing is powered.
Not to mention the mechanical hazard from the twirly twiddly bits.

JimB

I would either creat a local grounding rod and connect that to chassis, or used chiseled cable for your 300m cable run and connect the shield to grounded AC on the source side (proximal) wire and to your chassis on the distal end of the wire. To avoid creating antennas, I suggest the first (creat a local ground) and feed with two wires.

Thanks, i googled "chiseled cable" but drew a blank.....is this "armoured cable"?...cable with an outer metal shield?

This tethered drone looks like it has an armoured cable…and I suspect it is to act as a lightning conductor…just in case one strays into highly charged clouds (even on a sunny day)

Flyback said:

and I suspect it is to act as a lightning conductor…just in case one strays into highly charged clouds (even on a sunny day)

Click to expand...

i would guess that, like a helicopter, the rotating blades pick up a static charge in flight.