[SI-LIST] Re: impedance for 10-mile pipe at 120Hz, skin effect
- From: "Ingraham, Andrew" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 12 Dec 2003 17:24:09 -0500
Aballe73 wrote:
> I am trying to use PSPICE to model the behaviour of an electrified
> and buried pipeline (for natural gas or oil). ...
> ... There is a rectifier having one of
> these leads connected to the pipe, and the other lead connected to a
> grounding system: so a 120Hz rectified current is going through the
> ground into different points of the pipe and coming back to the
> rectifier through the pipe.
Yikes! I get scared when someone talks about mixing electrical current with
potentially explosive chemicals. I hope that sufficient safeguards will be
provided, but still, it scares me (even if the scenario I envision of a
spark igniting the gas could "never" happen).
> I understand that I should not considered the system as a
> transmission line because is too short (10 miles or so) compared to
> the current frequency (120Hz).
This is not correct. You can always treat it as a transmission line even
when it is very short.
It's the opposite that you need to watch out for ... using a lumped circuit
approximation when it is electrically long. But there is nothing really
wrong about using transmission line theory when it is electrically short.
The transmission line theory still holds! It's just that transmission line
theory can be mathematically difficult, so people try to find alternatives
(like lumped equivalent circuit models) when the full transmission line
treatment isn't absolutely necessary. Plus, in time-domain simulations,
skin effect resistance has traditionally been easier to do using lumped
models rather than transmission line models.
Regards,
Andy
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