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Re: Input Power Measurement



Subject:       Re: Input Power Measurement
       Date:   Tue, 27 May 1997 06:20:51 -0700
       From:   Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization:  Stoneridge Engineering
         To:   Tesla List <tesla-at-pupman-dot-com>
 References:   1


Tesla List wrote:
> 
> Subject:     Input Power Measurement
>        Date: Mon, 26 May 1997 23:42:39 -0700
>        From: Skip Greiner <sgreiner-at-wwnet-dot-com>
> Organization: Greiner, Ltd.
>          To:  tesla list <tesla-at-pupman-dot-com>
> 
> Hi All
> 
> It is obvious to all that any given transformer can be run in excess of
> its rating. Thus, a 1kva transformer may be run with 2kva input and
> live. This does not mean that the TC is being run at 1kva since the
> transformer is rated at 1kva.
> 
> How can the actual input power to the TC be measured????????
> 
> We can know the input voltage, I think, since most of us run from the
> mains (except those that insert a variac and transform the mains voltage
> up to 130v or 140v). We can still measure the output voltage of the
> variac, I think, and therefore know the input voltage.
> 
> BUT....how can the input current be measured. I seriously doubt that it
> is sinusoidal. There are ac ammeters, several different types which give
> an indication. Is there one type of ammeter, the reading of which could
> be multiplied by the voltage as obtained above, which would give an
> input power which all of us could use for comparison purposes?
> 
> I have a commercial instantaneous reading wattmeter. Does it provide any
> usable information? For instance....if I compare the input power to two
> different systems which use different types of input
> transformers....will I indeed be able to say that one system is more
> efficient than the other?
> 
> Any suggestions would be appreciated.
> 
> Skip

Skip,

While precise measurement of input wattage is quite difficult due to the
non-sinusoidal input currents, the wattmeter should provide a useful
relative comparison when the systems are run at similar break rates. 

-- Bert --