Old Generator Excitation Method

https://en.wikipedia.org/wiki/Excitation_(magnetic)

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thanks for replying. I am looking for a particular excitation method, I am already aware of most modern methods but this configuration is old, I would think 1960s.

It would be helpful to others when, once found, the <...Old generator excitation method...> were to be added to the Wikipedia article; anyone can edit Wikipedia.

https://forum.allaboutcircuits.com/threads/3-phase-brushed-generator-avr-problem.100529/

Maybe I wasn't clear enough, I am an electrical engineer and I repair generators, I obviously know generator excitation. please stop sending general information about this.

I encountered an old generator from the 1960s with an odd excitation configuration (like I described in the original post) I researched it and was able to find a document about this configuration with wiring diagrams and a troubleshooting guide and I was able to repair the generator. that was back in 2015.

Now, I lost the document and I have another generator with the same configuration that needs repair, I have looked everywhere in google for that document but I couldn't find it and I don't remember where I got it from or what keywords I used to search. What I am asking is, I need at least a name for this configuration so that I can google it or something.

No need to get huffy........"odd excitation configuration " is not very concise as a description, what is the excitation method? what is the brand name?, pmg ? brushes?

https://www.generatorsource.com/Generator-Excitation-Methods.aspx

..."In Static Excitation System, power for providing field excitation is derived from the Generator output terminals. A transformer know as Excitation Transformer, is connected to the output terminals of Generator to step down the voltage to required voltage level usually 415 V AC. As we need DC supply, therefore Transformer output is connected to a Thyristor Full Bridge Rectifier. Figure below shows simplified block diagram of Static Excitation System."...

https://electricalbaba.com/static-excitation-system-working-principle/

<...obviously know generator excitation. please stop sending general information about this...>

Please don't foreclose on solutions in deference to others who don't know, and to whom these things are not <...obviously...> apparent.

something like this:

the coil marked 11 would be the rotor winding, 27 and 28 would be the brushes.

there is no AVR, only three transformers and a three phase rectifier.

Transformer or bus fed static exciter system...

https://www.reivax.com/us/what-is-an-excitation-system/

I would just call it a "3 phase self-excited synchronous generator".

It starts up using a residual magnetism in the core, and if it hasn't been run for a long time, the field may need to be flashed to restore this residual field.

"the field may need to be flashed"

is this the reason they used to install a capacitor in the system?

G.E. made a system called Static Exciter for their Lynn size units, I think made in Waynesboro. They use a PPT (voltage transformer) to supply initial excitation, and then used Saturable Current Transformers in the stator leads. These SCTs were located in the neutral side of the stator windings, and provided excitation proportional to the armature current. During a short circuit, the support of the SCTs was critical to supporting the power system voltage & stability. The control windings of the SCTs were used to control the rotor current, similar to how on load tap changers are implemented on large power transformers, where the actual load current & voltage is not switched to affect the effective transformer voltage ratio.

This may be enough to find details on the Internet, not sure if I still have the manuals for this equipment...

I’m surprised that this design is not now common, as it seems to solve power system stability rather neatly & economically.

Found this...

http://www.e2powersystems.com/pdf/Retrofitting_SCTPPT.pdf

https://store.gegridsolutions.com/Manuals/Documents/General/GEK-14772A.pdf

https://www.gasturbinecontrols.com/sct-ppt/

Thank you all for your replies.

I managed to get a picture of the alternator connection:

as you can see, on your right there is the transformer. the main winding wires (red, green, white) go through the transformer and then exit to the terminal on the left where they get bridged together as a star point. the other ends of the winding (same colors) go directly to the same terminal. there are also three smaller gauge wires with the same colors as the main winding coming out of the alternator and going through the transformer as a secondary winding, the other ends exit the transformer to the two full bridge rectifiers (bottom left) that act as a three phase rectifier. the DC output from the rectifier goes directly to the brushes to the field winding on the rotor. there is also a varistor connected across the DC output.

the white cube in top left is an EMI filter, it has four wires. three wires are connected to the three phases L1, L2 and L3, and the fourth wire is connected to the alternator body (ground).

Please note that this configuration does not use an AVR, the output voltage regulation is done by the transformer/rectifier combination.

the following wiring diagram is from the manual of the alternator, made by Zanardi Alternatori:

so this pretty much cover it all. however, I am still unable to find the document that I am looking for and it looks like I am about to give up looking. I need that document because it has a detailed wiring diagram and a troubleshooting guide.

This is similar to the SCT excitation method except uses residual magnetism for no load excitation, instead of PPT, and has no control windings on the SCTs with which to fine tune the VAR output. This is a much smaller generator than I was imagining, so control is not as sophisticated.

Very clever design, excitation proportional to load, not too much to go wrong. Shorted or open rectifiers, bad brush rigging, turn to turn or ground fault on one or more of the excitation transformers. An oscilloscope on the field voltage should tell you what’s going on, unless you can’t run the generator...