High Voltage in Generators

<...any idea what may cause the problem?...>

Would this be an original-equipment-manufacturer-rewound exciter winding or some local knock-off?

Would this equipment have been serviced by a Technician from the original equipment manufacturer under warranty or an after-warranty service purchase order, or is the <...serviceman...> from somewhere else?

<...is this a good practice?...> Ask the original equipment manufacturer!

If the <...original equipment manufacturer...> [OEM] rewound the exciter, why did the OEM not reinstall it and recommission the equipment? Is this a case of wanting to do the work "on the cheap"? And is this thread a thinly-veiled ambition of wanting to sort the problem out for nothing?

Usual defect investigation question ... "What has changed since it was working properly?"

You have answered that by mention of the re-wind.

Probably the magnetic flux (excitation) has been changed due to change to any one (or more) of number of turns, wire diameter, wire resistance per unit length, copper purity, tightness of the rewind (air gaps in coil), exciter out of position and so on.

Maybe even needs to be "tuned" after such an action.

As far as what might happen with the serviceman performing various other seemingly random "adjustments", this could lead to catastrophic failure (Sparks/flames/smoke etc.) or just failure and the eventual contact with the supplier who will be able to rectify the problem with an associated cost.

The <...cause of the burn out...> took place before the equipment was rewound. That cause is a failure of the organisation to correctly install, and maintain the settings of, the protective device(s).

Yes any number of causes are possible....

https://stamford-avk.com/sites/default/files/literature/fault-finding-manuals/TD_FAULT_MAN_GB_JULY_2009_GB.pdf

Blame is in the domain of the legal profession, which makes money out of people's misery, a profession that is two steps up from prostitution as far as disdain is concerned (the one in the middle being the Estate Agent). Blame is not a useful approach in Engineering.

"When you point a finger at someone, look closely at where the other three are pointing" _{- Anonymous poster #0}

1) "... any idea what may cause the problem?...", Yes, a lack of qualified service personnel.

2) '... is this a good practice?...', Never.

3) "...what may (it) lead to (?)...", "...high voltaging (sic) after installation...", destruction/downtime of equipment, death/injury to personnel, etc.

Then blame the individual who decided to adopt that particular approach, and not the <...serviceman...>, who was merely carrying out that individual's chosen course of action.

The problem seems to be some type of electronagnetic interference. Case study will require all of the documentation, so you better talk to someone going to invest all that time.

Reducing voltage switching cables in the terminal box may lead to overheating of equipment. I would check temperatures with a thermal camera just in case.

Thank..!! such a very nice information..