RE: Input power measurement

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John H. Couture by way of Terry Fritz <teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Paul -

I obviously didn't do my homework on this one. The lamp test is a good idea
but as you pointed out it only measures the total current not the active
current. The lamp does work well for measuring the TC secondary current as
shown in the TCC Guide. But for input wattage it appears that coilers will
have to use the standard electrodynamometer type of wattmeter for measuring
the TC power. For most TC wattage measurements this will be the least
expensive method and the accuracy would be within (+/-) 5.0 percent. Thank
you for bringing this error to my attention.

John Couture

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-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, March 15, 2003 2:32 PM
To: tesla-at-pupman-dot-com
Subject: Re: Input power measurement


Original poster: "Paul Nicholson by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

John,

  > The electrical current triangle consists of the Active
  > (Incan Lamp), Total (Std Ammeter), and Reactive (Calcs) currents.

Unfortunately, the lamp power is proportional to the square of the
total current, not the square of the real (aka active) current.

It is registering the 'active' power alright - but the active power
in the lamp, not in the circuit as a whole.  The active power in
the lamp is (total_current)^2 times the lamp resistance.

The lamp is aware of only the line (total) current and its own
voltage drop, and not the line voltage.

As gary says, there's no way to register the effect of the phase
angle between circuit current and load voltage using a lamp.

--
Paul Nicholson
--