Ever thought about ... ?

Part of the test is a fine wire connecting a metal enclosure to the 'suitable point' of the source (e.g. neutral) - this wire mustn't melt. 

How funny it is that the world joins up round the back.

This reminds me of a problem I was involved with at one time.

Large transmitter valves ( really big like 10kV of HT and 5 amps of anode current, with DI water cooling holding off the anode voltage accross the hoses) occasionally flash short and this is blamed on passing cosmic radiation, or  some other ill-explained effect. If the supply has too much decoupling capacitance, then the high surge currents mean chunks are blasted out of the cathode when this happens, and the device is quickly destroyed. So various fast shutdown crowbar circuits with thyratrons and later SCRs have been developed combined with the option of a series 1kW fire element, as a permanent kilowatt to sweat, but a to act as a known limit to what we would recognise as PSSC.

So how do we know the protection circuit functions as expected.

How to test it without risking that device worth more than my car ?

In an Eimac application note written in the era of pipe smoke and slide rules when such transmitting valves were new, came a suggestion for those of of sufficient MF not to be afraid to run the kit with the lid open.


An insulated rod may be used to introduce a length of earthed 5A fuse wire to form a short circuit between the energised anode and the casing. If the protection circuit successfully limits the discharge to a safe level, the fuse wire will remain intact, and the supply will shut off gracefully and be ready for a restart.

Well mugger be, that's not one for those who are not fully confident in their design is it? if the trip does not operate you get blasted with ex fusewire ....!!

We dragged this technique into the late 20th century with an HV relay and a better defined fuse rather than holding an insulated prodding stick by hand, as even with gloves and goggles it just felt wrong. In effect the test  measures the let through or I2t of the shutdown mechanism as being less than the fusing energy of the test fuse, though it did not say so.

I now wonder if the folk who wrote it knew of each other's use of the method.

regards

Mike.

Part of the test is a fine wire connecting a metal enclosure to the 'suitable point' of the source (e.g. neutral) - this wire mustn't melt. 

How funny it is that the world joins up round the back.

This reminds me of a problem I was involved with at one time.

Large transmitter valves ( really big like 10kV of HT and 5 amps of anode current, with DI water cooling holding off the anode voltage accross the hoses) occasionally flash short and this is blamed on passing cosmic radiation, or  some other ill-explained effect. If the supply has too much decoupling capacitance, then the high surge currents mean chunks are blasted out of the cathode when this happens, and the device is quickly destroyed. So various fast shutdown crowbar circuits with thyratrons and later SCRs have been developed combined with the option of a series 1kW fire element, as a permanent kilowatt to sweat, but a to act as a known limit to what we would recognise as PSSC.

So how do we know the protection circuit functions as expected.

How to test it without risking that device worth more than my car ?

In an Eimac application note written in the era of pipe smoke and slide rules when such transmitting valves were new, came a suggestion for those of of sufficient MF not to be afraid to run the kit with the lid open.


An insulated rod may be used to introduce a length of earthed 5A fuse wire to form a short circuit between the energised anode and the casing. If the protection circuit successfully limits the discharge to a safe level, the fuse wire will remain intact, and the supply will shut off gracefully and be ready for a restart.

Well mugger be, that's not one for those who are not fully confident in their design is it? if the trip does not operate you get blasted with ex fusewire ....!!

We dragged this technique into the late 20th century with an HV relay and a better defined fuse rather than holding an insulated prodding stick by hand, as even with gloves and goggles it just felt wrong. In effect the test  measures the let through or I2t of the shutdown mechanism as being less than the fusing energy of the test fuse, though it did not say so.

I now wonder if the folk who wrote it knew of each other's use of the method.

regards

Mike.