Re: LF: 33 Hz QRM

[David Hine <evad_hine@yahoo.co.uk>]

Hi, A very interesting article. The London Underground (Metro) uses a low voltage 4 rail DC system. The 2 'live rails are  balanced + and - with regard to the running rails. This system is a 'throw-back' from the days of DC motors and this system reduces corrosion causing currents to flow in the running rails and other track equipment. There is a lot to be said for the self contained diesel units that require no external power supplies with all that infrastructure. Imagine how useless the electric system would be in times of extreme weather or disasters, man made or natural.

 The same applies to modern digital radio communications (with all its necessary infrastructure and thousands of tiny transmitters) when compared to the old Long Wave AM broadcasting, where a single large transmitter covers a whole continent. Nowadays 'progress' always results in over-complicated and 'fragile' systems that fail too easily when 'nasty things happen'.

With very kind regards, Dave.

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From: Johan Bodin <jhbodin@tele2.se>
To: rsgb_lf_group@blacksheep.org
Sent: Tuesday, 29 March 2016, 8:11
Subject: Re: LF: 33 Hz QRM

That problem can be solved by using a return line and booster transformers that minimises current leakage into surrounding earth:

https://library.e.abb.com/public/f1200714de5086c585257d7300287357/1LFI2026%20special%20power%20transformers%20for%20railway%20-%20brochure%20EN.pdf

73 de
Johan SM6LKM

Den 2016-03-17 kl. 15:18, skrev Andy Talbot:

Is that to minimise skin loss in steel track ?

UK Third rail is, of course, DC, and I once spent an idle moment calculating the loss if 50Hz AC were to be used with magnetic iron conductors.  I think I came to the conclusion a 1MW train could probably travel a few hundred metres before it lost its power supply.

andy  G4JNT

On 17 March 2016 at 13:21, Johan Bodin <jhbodin@tele2.se> wrote:

Railway QRG is 16 2/3 Hz in Sweden too.

73 de Johan SM6LKM

John Rabson wrote:

I seem to recall that some railway systems use at about 16 2/3 Hz (one third of 50 Hz) for traction.

...

Can someone say whether my recollections are correct, please?

73 John F5VLF