Re: LF: G4HUP aerial current meter/ hazards

[Andy Talbot <andy.g4jnt@gmail.com>]

Leaving the secondary of a current transformer open-circuit  once caused half a city to be blacked out when the 400kV grid network tripped

http://www.g4jnt.com/Hams_Hall_Investigation_Report.pdf

Quite a long report, but well worth a read.  Paragraph 69 covers the findings that smoke was coming from the control equipment as a current transfomrer hadce been withdrawn from servicwe, but left in place witho O/C secondary.

Andy  G4JNT

On 5 August 2017 at 07:53, Wolfgang Büscher <dl4yhf@freenet.de> wrote:

... and never forget to wind a 'secondary' over the current transformer, always terminated with low resistance. Otherwise you will quickly saturate it, which is something that NO current transformer will tolerate at moderate levels !
Running a current transformer with an "open secondary" (or non-existing secondary) should be avoided.

Cheers,
 Wolf .

Am 05.08.2017 um 07:38 schrieb Dr. Wolf Ostwald:

good morning !
a current transformer with ferrites of unknown origin and virtues is a very risky thing.
As these cores are widely available on swapmeets its a lure to use them.
But they can be tested. I blew a few of them by just putting them on with a single primary turn and with power less than a hundred watts they got hot and broke.
The losses can be extremely high.
It does not help to measure their magnetic constant. As that has not much to do with frequency dependent losses.
a way to find out is to use a 50 ohm load and measure the RF voltage across the terminals. Then u just put the toroid over the "hot" side of the resistor terminals.
If the measured RF voltage drops heavily, the core is useless. You dont want it to block, u want to derive some RF for measuring purposes.
The above core would go into pieces and additionally as it poses a high inductance to ur feedline, the amplifier stage may go south, depending on the safety factor involved with ur construction .

73 de wolf   df2py