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Input Power Measurement



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