Re: Input power measurement

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

Original poster: "Crow Leader by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

Hello.

You are confusing watts and VA. The input to your transformer may very well
be 2000VA, but probably not watts which are real work. Because of your
configuration, and the resonance going on, you have high circulating
currents. Part of the time your transformer is pulling way more current than
it "needs" and the other half of the time it's actually supplying power back
into the outlet. This difference between the current times volts you are
measuring vs. the amount of work really being done (watts) is called power
factor. In your case,  it sounds like you may be using twice as much VA as
power, giving you a poor power factor of around 50%.

This is considered bad because it heats up your wiring more than you'd want,
and is pretty wasteful. You can correct this by connecting an amount of
capcitors across the input terminals to your transformer. With the right
value, they will cancel each other out. You may still have 17A circulating
between the cap bank and the transformer, and you will still have a decent
amount of heating in the transformer, but the current between the capacitor
bank/transformer and outlet will drop to approximately the amount of power
you are really using / line voltage.

KEN


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, March 08, 2003 1:52 PM
Subject: Input power measurement


 > Original poster: "Skip Greiner by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <sgreiner-at-wwnet-dot-com>
 >
 > Hi all
 > I am using a 9kv at 120ma NST. In operation I use an iron vane ammeter
 > (known to be within 5% accuracy) to monitor current. My mains voltage is
 > nominally 117V. Interestingly the current into the NST is about 17A when
 > running in resonant mode. It is my understanding that an iron vane meter
 > reads true input current regardless of waveform. Therefore my input power
to
 > the NST is nearly 2000 watts.
 >
 > I would appreciate comments from anyone who can help explain the
discrepancy
 > between the 1080va rating of the "current limited NST and the measured
input
 > in resonant mode operation.
 > Skip
 >
 >
 >