[TowerTalk] Lightning Protection for Orion Rotor

[Grant Saviers]

If the ball bearings in the rotator and "thrust" bearing are operating 
as intended then an oil film is insulating the races from each other and 
from the balls.  Every rotator I've disassembled has no electrical path 
around the bearings.

I've watched the arcing across a motor ball bearing oil film on a scope, 
and seen it in disk drive read signals.  If a polymer "thrust" bearing 
is used on a tower then even higher voltage isolation is present at that 
point.  The charge comes from air friction against the antenna or disk.  
The oil film breakdown is on the order of 10's of volts.  VFD powered 
motors are known to have potentially serious bearing problems from the 
high frequencies the VFD's put into the windings, coupled to the shaft 
and the potential is created to the frame across the bearing. 
http://est-aegis.com/TechPaper.pdf

The consequence of not grounding around the rotator bearing is pitting 
of the balls and races by the arcs and also RF noise generated near the 
antenna.  Also, having a heavy gauge wire from mast to tower top is 
likely to be helpful in a strike. The tower probably also acts somewhat 
as a Faraday cage to shunt currents to the outside of the structure and 
away from the rotator.

MOVs provide overvoltage protection but have a downside as they degrade 
with every snubbing shunt and eventually fail.  On an AC power strip, a 
failed to short MOV burned up a nearby ham's shack here when the plastic 
power strip case ignited.     If on antenna control lines, sufficient 
degradation can be experienced over time to prevent normal operation.  
As one antenna manufacturer discovered before they switched to TVS  
diodes.  Of course any transient suppression device can be vaporized 
with sufficient power surges, but some pretty hefty capacities are 
available.
http://www.littelfuse.com/products/tvs-diodes.aspx

Grant KZ1W

On 12/24/2016 16:18 PM, john at kk9a.com wrote:
> Unless you enjoy repairing rotators, I would. I have either MOVs or GDTs on
> all of my motors and indicating sensors. I have not made any additional
> effort to ground the mast, it seems like the bearing and rotator housing
> would both already have that covered.
>
> John KK9A
>
> To:	towertalk at contesting.com
> Subject:	[TowerTalk] Lightning Protection for Orion Rotor
> From:	William Saulnier <caseydogmusic at gmail.com>
> Date:	Fri, 23 Dec 2016 11:16:44 -0600
>
> At the risk of starting yet another discussion of lightning protection in
> general I do have the following specific question.
>
> In addition to an overall sound design for grounding, etc. is there a
> significant advantage to having rotor control line surge suppressors at the
> top of the tower? I have read that its a good idea to ground the mast to
> the tower to bypass the rotor and I was already planning to have
> suppressors on the control lines at the bottom of the tower and at the
> entry to the radio room. The intent would be to have better protection for
> the rotor itself especially its apparently sensitive reed switch.
>
> Thanks.
> Bill N5VR
> ___________
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>