Transformers

We built a large 400 hertz power supply for subs back in 1960.
It had to have a certain form factor to get it down through the hatch.

Hi Bushbadee,

Yes, that was one of the requirements of many pieces of submarine
machinery!!! (even the main feed pumps I worked on several different
400 hz sets, perhaps the oldest was 400HZ, 120V 3phase 42kW motor-generator
sets used on the old Permit class (renamed after the Thresher accident in
'63). IIRC, these were all mag-amp units. The only 'electronic' thing in
them was the silicon rectifiers.

daestrom

 

OUr converters were to replace motor generators.
Lots of 2N174's
the output was 120 volts, 3 phase.
I wonder if there was any relationship.

 

I did also work on some smaller power 60hz to 400hz converters. IIRC, they
had two 400hz inverters feeding a Scott-T for the 3 phase output. One
'master' that fed main leg, and the 'slave' feeding the tee-leg. Phase A-B
voltage controlled by master, phase B-C and C-A controlled by not only
magnitude of 'slave' inverter, but phase shift delay from 'master'. But
these were smaller units, only a couple of kW.

daestrom

 

--
Don Kelly

remove the urine to answer

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In this case there was probably a voltage regulator which acted to hold
output voltage constant. In the case of a change in load, there would be a
signal to raise the field current. With a high gain regulator and high field
time constant, the use of a time derivative signal in addition to a
proportional signal would be a benefit.
In the original case the machine was a series machine so field current would
be the same as the load current.
-------------------

------------
Mag amps were hot items before SCR's came into use. They essentially served
the same purpose and, at the time (1950's) were very useful for field
control of generators -with faster response than previously available
techniques for such purposes as excitation systems for alternators. In
addition to a speed advantage there was also a saving in cost, physical
size, complexity and maintenance. Another use was for dimming of theater
lights. Simply a case where a technology came in that was better than
what was there before and, in its turn, became obsolete for most
applications when solid state devices became capable of handling the same
currents and voltages.

 

(shudder!!!) I just had a flashback of re-brushing Amplidynes used for some
old excitation systems ;-) Twice as many brushes as similar sized DC
machinery. Considering the occasional failures I say of SCR systems, always
thought mag-amps were the best.

daestrom

 

At least the amplidyne had a reasonable response in comparison to the pilot
exciter-exciter-field set up and used less space -with only one commutator.

 

We built them also.
Did you by chance work for ElectroSolids or a competitor.?

I worked on an interesting one.
It was a pulse width modulated inverter. ac amplifier.
An Input ac signal was amplified and rectified.
That signal then acted as the reference for a pulse width modulated
converter which chopped at double 40 Kc.
The amplified half wave rectified signal was then fed to the center tap of a
transformer which the then derectified the imput wave by haveing a pair of
transistors which were tied to the input and detected 0 crossing of the
input wave and kept the out put transistors in sync with the input.

The thing was pretty flat to 4KC and down to about 20 cycles.

The output had about 5% distortion.
One of my ideas was to feedd the amplified signal to a class B or even a
Class A amplifier as the DC input so the dc on the amplifer would track
the output and achieve higher efficiencies than the theoretical efficiencies
of class A and B amplifiers.

I think Sony took out patents on the idea, but their patents were useless
after I had presented papers on the theory and device we had built to the
IEEE about 20 years before their patent.

DR Middle brook also used the same idea to come up with a similer amplifer,
but he used a bridge output and not a transformer which has quite a few
advantages.
I do not know if David ever built t he device, but we built, demonstrated
and packaged our device and tried to market it as a high efficiency shake
table driver.