From: Richard Prosser <rhprosser@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 21 Oct 2021 00:15:17 -0700
Subject: Re: [EE]: Calculating phase shift in high voltage A/C distribution
	cable
Thread-Topic: [EE]: Calculating phase shift in high voltage A/C distribution
	cable
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For a polyethylene cable,  Vp is likely to be around 0.67,(crosslinked poly
may be slightly lower  ~0.65?) If it's PVC the Vp will be still lower,
maybe 0.5 but varies with frequency - not an issue in your case. Otherwise
your calculation looks about right. (0.9 degrees if Vp =3D 0.67).
But this is for the difference between the 2 feeds - ie one feed is 10km
longer than the other, assuming the same source supply and there are no
phase inversions  (eg at transformers) etc.

RP

On Thu, 21 Oct 2021 at 14:05, Justin Richards <justin.richards@gmail.com>
wrote:

> I think for RF there are coax cable constants for Vp or Vf which I am
> guessing is Velocity of Propagation or Velocity Factor.
>
> However, with High Voltage A/C @  50Hz does the question of phase shift
> make sense.
>
> And if so, what would be a typical value for Vp or Vf.
>
> I ask as it appears that there was a situation where there were two ring
> mains fed from each end with no "opens" and thus the way I see it is the
> output of each HV step up transformer would be connected to each other vi=
a
> a long length of cable.
>
> Assuming two identical transformers (which will not be the case), I would
> guess that if the outputs were directly connected at the transformers the=
n
> hypothetically no big deal.  No sparks, no increase in load etc. (again
> assuming the connections were around the right way)
>
> However, if the interconnecting cable was extended then I am guessing as
> the length increased the phase shift would increase and the two
> transformers would be fighting each other.
>
> Does that sound reasonable.  And if so, how do I calculate phase shift ov=
er
> the cable at 50Hz.  Can I assume a Vp of 1, or Velocity of propagation as
> the speed of light.
>
> So 33uS over 10kms ~
> @50Hz, T is 20mS (360 degrees)
> Phase shift =3D (33uS/20mS)*360
> ~ 0.6 deg phase over 10kms.
>
> Am I way off.
>
> Welcome any insights anyone may have.
>
> Regards Justin
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