[Amps] Power Supply Turn Off Under Load

[Roger (Sub1)]

On 1/17/2011 11:17 AM, TexasRF at aol.com wrote:
> There have been a couple of recent mentions of the bad effects of turning
> off a hv power supply that is under full load.
>
> A google search didn't turn up useful information so I am wondering if a
> reader here might have some insight as to the problems associated with an
> under  full load shutdown?
>
> This is the scenario where a 240vac primary breaker or fuse lets go during
> a transmission at full carrier level such as AM, RTTY or one of the current
>   Digital modes.

With an inductive load such as a transformer, IF the circuit is broken 
at the peak of the AC cycle (worst case) the Reverse EMF created by the 
collapsing current will induce a tremendous back, or reverse voltage.  
An inductor opposes any change in current and the collapsing field will 
generate that reverse EMF. As the field is changing abruptly the 
resultant voltage will be higher than normal.    This spike not only 
goes back on to anything connected to the primary of the transformer, it 
is "transformed" through the transformer as a series of reducing 
amplitude spikes on the input (ringing). So the initial spike on the 
output of a HV transformer can be considerably higher than the normal 
voltage and exceed the ratings of rectifiers, capacitors, etc...

73

Roger (K8RI)
>
> Thanks/73,
> Gerald K5GW
>
>
>
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