Delivered-To: daveyxm@virginmedia.com Received: by 10.50.237.98 with SMTP id vb2csp651871igc; Fri, 27 Dec 2013 18:09:12 -0800 (PST) X-Received: by 10.180.14.231 with SMTP id s7mr23211122wic.1.1388196551290; Fri, 27 Dec 2013 18:09:11 -0800 (PST) Return-Path: Received: from post.thorcom.com (post.thorcom.com. [195.171.43.25]) by mx.google.com with ESMTP id h6si13690018wjr.63.2013.12.27.18.09.10 for ; Fri, 27 Dec 2013 18:09:11 -0800 (PST) Received-SPF: neutral (google.com: 195.171.43.25 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) client-ip=195.171.43.25; Authentication-Results: mx.google.com; spf=neutral (google.com: 195.171.43.25 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) smtp.mail=owner-rsgb_lf_group@blacksheep.org Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Vwj16-0001aW-BC for rs_out_1@blacksheep.org; Sat, 28 Dec 2013 01:48:40 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Vwj15-0001aN-Od for rsgb_lf_group@blacksheep.org; Sat, 28 Dec 2013 01:48:39 +0000 Received: from relay2.uni-heidelberg.de ([129.206.210.211]) by relay1.thorcom.net with esmtps (TLSv1:AES256-SHA:256) (Exim 4.77) (envelope-from ) id 1Vwj12-0004pn-Lz for rsgb_lf_group@blacksheep.org; Sat, 28 Dec 2013 01:48:38 +0000 Received: from freitag.iup.uni-heidelberg.de (freitag.iup.uni-heidelberg.de [129.206.29.204]) by relay2.uni-heidelberg.de (8.13.8/8.13.8) with ESMTP id rBS1mZls011032 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Sat, 28 Dec 2013 02:48:35 +0100 Received: from [129.206.22.206] (pc206.iup.uni-heidelberg.de [129.206.22.206]) by freitag.iup.uni-heidelberg.de (8.12.11.20060308/8.11.2) with ESMTP id rBS1mZZi023338 for ; Sat, 28 Dec 2013 02:48:35 +0100 Message-ID: <52BE2DE8.1060405@iup.uni-heidelberg.de> Date: Sat, 28 Dec 2013 02:48:24 +0100 From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <2f507c1ff91346b2b8adba0518611224@kabelmail.de> <39966C71EF4543899F81399598C190F7@Extensa> <52BBFDC4.3010507@psk31.plus.com>,<52BC272F.7040803@iup.uni-heidelberg.de> <52BC683B.5030107@iup.uni-heidelberg.de> <032001cf02d7$462ca970$d285fc50$@comcast.net> In-Reply-To: <032001cf02d7$462ca970$d285fc50$@comcast.net> X-Spam-Score: -2.9 (--) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Hello Jim, Bob, VLF, I assume such a PD inception detector will not work in this setup because there are permanent audible and visible discharges when running the VLF transmitter. Of course all this can be avoided using E field steering elements like a toroid out of aluminium tube, like that one http://www.grosshandel-knajp.de/images/img/fck/rohr_gl.jpg I've used some of these tubes for 200 kV stuff at work some years ago. Maybe an idea for Bob! They are available with a diameter of say 6 cm? Not expensive and light weight! Hide the end of the antenna wire into the center of such a toroid, maybe having 20 cm diameter and the arcing problems will be gone! Anyway i think that it will be to late if you stop transmitting after detecting PD coming from a beginning insulation breakdown of the enamelled cu wire. Eventual raindrops falling between the turns will deform the E field dramatically and cause high local field strength, that's my fear. [...] Content analysis details: (-2.9 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -2.3 RCVD_IN_DNSWL_MED RBL: Sender listed at http://www.dnswl.org/, medium trust [129.206.210.211 listed in list.dnswl.org] -0.6 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 0.0 HTML_MESSAGE BODY: HTML included in message X-Scan-Signature: 94b4899eb522d3cd83a8c4d63d16b91e Subject: Re: VLF: 8969.99 Content-Type: multipart/alternative; boundary="------------050709070004030600070409" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=HTML_40_50,HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false Status: O X-Status: X-Keywords: X-UID: 3510 This is a multi-part message in MIME format. --------------050709070004030600070409 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by relay2.uni-heidelberg.de id rBS1mZls011032 Hello Jim, Bob, VLF, I assume such a PD inception detector will not work in this setup=20 because there are permanent audible and visible discharges when running=20 the VLF transmitter. Of course all this can be avoided using E field=20 steering elements like a toroid out of aluminium tube, like that one=20 http://www.grosshandel-knajp.de/images/img/fck/rohr_gl.jpg I've used=20 some of these tubes for 200 kV stuff at work some years ago. Maybe an=20 idea for Bob! They are available with a diameter of say 6 cm? Not=20 expensive and light weight! Hide the end of the antenna wire into the=20 center of such a toroid, maybe having 20 cm diameter and the arcing=20 problems will be gone! Anyway i think that it will be to late if you stop transmitting after=20 detecting PD coming from a beginning insulation breakdown of the=20 enamelled cu wire. Eventual raindrops falling between the turns will=20 deform the E field dramatically and cause high local field strength,=20 that's my fear. 73, Stefan/DK7FC Am 27.12.2013 08:42, schrieb hvanesce: > > Stefan, > > If arc-induced breakdown paths between turns is an issue, have you=20 > considered adding a homebrew corona inception detector with feedback=20 > to the modulator or switch driver? I haven't made one for a VLF coil,=20 > but it might be worth a try if repairs are an issue; there is good=20 > precedent at near-VLF frequencies. > > The idea would be to limit voltage or skip cycles before breakdown=20 > occurs; the voltage-limiting method could often be nearly transparent=20 > to real-time operation. > > If repairs are rare then the above might not be worth it, just thought=20 > I'd mention the possibility. > > 73, Jim AA5BW > > *From:* owner-rsgb_lf_group@blacksheep.org=20 > [mailto:owner-rsgb_lf_group@blacksheep.org] *On Behalf Of *Stefan Sch=E4= fer > *Sent:* Thursday, December 26, 2013 10:33 AM > *To:* rsgb_lf_group@blacksheep.org > *Subject:* Re: VLF: 8969.99 > > Hi Bob, > > Of course, if the coil is protected against rain, then it is no=20 > problem. But the coil is quite large and due to the high voltage, the=20 > housing should ideally have a distance of 30cm or more to the coil. So=20 > the housing must be quite large, even more. And that makes it=20 > dangerous because of wind blasts on the to of the building in 35m AGL... > Anyway it would be nice and i also thought about using a simple foil=20 > across the coil, without additional distance. > However on LF, there are partial discharges on the top of the coil=20 > which burns holes into the protecting foil. And the VLF winding is=20 > 2000m long. It is a lot of effort to repair it after a short cut=20 > between some turns due to arcing. So it is a high risk. > I think i will make a test in the near future and see if 9 kHz partial=20 > discharges are as agressive as 137 kHz partial discharges :-) > 73, Stefan/DK7FC > > --------------050709070004030600070409 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Hello Jim, Bob, VLF,

I assume such a PD inception detector will not work in this setup because there are permanent audible and visible discharges when running the VLF transmitter. Of course all this can be avoided using E field steering elements like a toroid out of aluminium tube, like that one http://www.grosshandel-knajp.de/images/img/fck/rohr_gl.jpg I've used some of these tubes for 200 kV stuff at work some years ago. Maybe an idea for Bob! They are available with a diameter of say 6 cm? Not expensive and light weight! Hide the end of the antenna wire into the center of such a toroid, maybe having 20 cm diameter and the arcing problems will be gone!
Anyway i think that it will be to late if you stop transmitting after detecting PD coming from a beginning insulation breakdown of the enamelled cu wire. Eventual raindrops falling between the turns will deform the E field dramatically and cause high local field strength, that's my fear.

73, Stefan/DK7FC


Am 27.12.2013 08:42, schrieb hvanesce:

Stefan,

 

If arc-induced breakdown paths between turns is an issue, have you considered adding a homebrew corona inception detector with feedback to the modulator or switch driver? I haven’t made one for a VLF coil, but it might be worth a try if repairs are an issue; there is good precedent at near-VLF frequencies.

 

The idea would be to limit voltage or skip cycles before breakdown occurs; the voltage-limiting method could often be nearly transparent to real-time operation.

 

If repairs are rare then the above might not be worth it, just thought I’d mention the possibility.

 

73, Jim AA5BW  

 

From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Stefan Schäfer
Sent: Thursday, December 26, 2013 10:33 AM
To: rsgb_lf_group@blacksheep.org
Subject: Re: VLF: 8969.99

 

Hi Bob,

Of course, if the coil is protected against rain, then it is no problem. But the coil is quite large and due to the high voltage, the housing should ideally have a distance of 30cm or more to the coil. So the housing must be quite large, even more. And that makes it dangerous because of wind blasts on the to of the building in 35m AGL...
Anyway it would be nice and i also thought about using a simple foil across the coil, without additional distance.
However on LF, there are partial discharges on the top of the coil which burns holes into the protecting foil. And the VLF winding is 2000m long. It is a lot of effort to repair it after a short cut between some turns due to arcing. So it is a high risk.
I think i will make a test in the near future and see if 9 kHz partial discharges are as agressive as 137 kHz partial discharges :-)
73, Stefan/DK7FC


--------------050709070004030600070409--