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TC Reflected Power - was 130kW Coil -- Oh No!
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From: John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent: Sunday, February 08, 1998 2:40 PM
To: Tesla List
Subject: Re: TC Reflected Power - was 130kW Coil -- Oh No!
Bill, All -
Thank you for your reply on measuring the reflected power for a large
Tesla coil. If I correctly understand the description of your
autotransformer and variable inductor they are setup similar to Fig 4c
shown in the Tesla Coil Design Manual. You have added duplicate metering on
each side of these two controls. The controls are adjusted for maximum
wattage and highest power factor as shown by the meters. This certainly
would give the best input power conditions for a Tesla coil. However, this
is not what I thought you were doing.
The tests I thought you had done were for reflected voltage or VSWR
(voltage standing wave ratio) which are sometimes called reflected power
tests. To radio hams this is better known as SWR tests and is a relatively
simple test that you are no doubt familiar with. This test measures the
foward voltage (power) going from the radio transmitter to the load
(antenna) and the reflected voltage from the load to the transmitter. The
voltages are measured using a bridge circuit and a high impedance voltmeter.
The equation is
VSWR = (Vf+Vr)/(Vf-Vr) Vf = foward voltage Vr = reflected voltage
This test for radio is relatively simple because the system of transmitter,
transmission line, and antenna is well defined. This test for Tesla coils is
not as easy to outline. The Corums have said they have performed this test
on one of their coils but gave no details. I have not been able to find that
anyone else has successfully done this type of testing. I have tried to work
out a test but have not been successful.
The advantage of the SWR test for radio work is that it is an indication
of how well the system is working and if it is properly tuned. This type of
test would also be of great value for Tesla coils as it would show if the
system is in proper tune and working efficiently.
At present the spark test is the only way to find if the Tesla coil is
working correctly and this is not a satisfactory test. The VSWR test would
be a superior method to verify that your TC system is operating properly.
Comments welcomed.
John Couture
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At 01:49 AM 2/7/98 -0600, you wrote:
>
>----------
>From: Wysock, William C. [SMTP:Wysock-at-courier8.aero-dot-org]
>Sent: Friday, February 06, 1998 8:34 AM
>To: Tesla List
>Cc: ttr
>Subject: RE: 130kW Coil -- Oh No!
>
>
>John, All,
>
>The manner and technique I use to measure reflected power
>on large Tesla coil systems is as follows. I measure actual
>wattage, amperage, and voltage at several key points in the
>controller's circuitry. Since a switchboard type kilowatt meter
>requires both a potential transformer and a current transformer,
>its reading is based on the relationship of the current phase
>angle with respect to the voltage phase angle, in that part of
>the circuit to which it is connected. Doing this, at the a.c. mains
>as well as across the primary of the H-V transformer, shows
>the relationship of total "forward" going power, vs. "reflected"
>going power. Since I employ the use of a high current
>continuously variable inductance, while the coil is energized,
>I can adjust load voltage and series inductance, and observe
>the readings on the two separate kilowatt meters. It is possible
>to adjust the autotransformer settings such that the load side
>of the controller shows a considerably lower KW reading, then
>is shown on the a.c. mains meter. Under this condition, the load
>ammeter will read considerably higher then the a.c. mains
>ammeter. This is reflected (out of proper phase relationship
>current.)
>
>In the same manner, when both KW meters read approximately
>equal, (both must be peaked,) then looking at the amp meters
>shows the lowest (and more or less equal) peak value, and the
>Tesla Coil system performance is at its best. An interesting note:
>when the Tesla Coil controller's adjustments have been "peaked",
>the load side voltmeter very clearly shows "resonant rise". This
>may be seen as an increase of over 50 volts in that part of the
>circuit.
>
>Bill Wysock
> -------------------------------------------
>Tesla Technology Research