[Amps] 3 Phase Transformer Expertise Needed

[Jeffrey Madore]

Dave,

Any other info on the nameplate?
Where did the transformer come from?
What does it look like?
What is the primary voltage?

>From the secondary resistance and the current rating, my first hunch is that
may be an industrial metering / relaying transformer. If so, this type of
transformer is usually located at a point (switchgear) where high voltage
needs to be monitored. The high voltage is transformed to something
reasonable (often 120v) and then fed to protective relays and or meters,
some of which may be remotely located. The two windings may serve different
functions such as: voltage / watt / VAR metering, under / over voltage
protection, phase loss, phase rotation, synchronization, frequency metering,
etc.  As part of these transformers there is sometimes a metering fuse
(special current limiting type) mounted on top.

As far as paralleling the secondaries, if the resistance of both windings is
the same, power it up with a 3 phase source and measure the voltage between
A and A1. If it is zero you can parallel them. If there is a voltage, you
will get circulating current; the value determined by the voltage and Z of
the windings. It's also nice if you can load the paralleled windings and
measure any circulating current. I've VERY carefully used a glass bowl of
water for a 1500 V load - very lightly salted to raise current as I
monitored. This has it's obvious risks and dangers.

Starting at a lower voltage and working up is always nice, but 3 phase
variacs aren't too common in the ham shack.

If I had my choice, I would rather use two 3 phase bridges and parallel the
DC out. Or series them for higher voltage.

Hope this is of some help,

Jeff - K1LE - CT ><>


----- Original Message -----
From: "David Smith" <vk3hz at wia.org.au>
To: <amps at contesting.com>
Sent: Monday, June 02, 2003 10:20 AM
Subject: [Amps] 3 Phase Transformer Expertise Needed


> I recently obtained a big 3-phase transformer that could be useful if the
> lights flicker too much with my single phase PSU!  However, I need some
help
> in working out what DC voltage and current the transformer will produce.
>
> The transformer has a primary with three separate windings coming out to
> binding posts and so I assume that it can be linked either as a star or
> delta configuration.  Currently it's wired as delta.
>
> There appear to be two separate secondaries.  Each secondary has 4
> connections - one winding marked A, B, C & N and the other A1, B1, C1 &
N1.
> Resistance measurements indicate that these are probably star
configuration
> (i.e. A-B = B-C = A-C = 200 ohms, A-N = B-N = C-N = 100 ohms).  The
> transformer is marked "1550 V RMS per phase, 0.35A RMS per phase".
>
> Can anyone advise what sort of voltage and current I'd get out of this
> transformer if I put a 3-phase bridge on the output of one of the
windings?
> What about combining the two windings?  Does anyone know anything about an
> Interphase Inductor or Interphase Transformer configuration for two
3-phase
> windings?
>
> Also, is there another place I should be asking these questions?
>
> Regards,
> David Smith
> VK3HZ
>
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> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>


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