Exciter Stator Failure - Cause ??? 2

[IOC-AUS]

Hello All,
Just trying to get an idea of a cause of failure on an AC Generator ( 125 kVA ).
See photo - this is the Exciter Stator.
The AVR had also blown on this machine.
The Generator Set is a Diesel Driven Unit Powering an Electric Pump Motor 55 kW with VSD / Soft Starter.
I welcome any Technical thoughts to help understand the possible cause of this failure from the attached photo.
Thanks in advance.

 

[TugboatEng]

Looks like a new unit. You're on the left side of the bathtub curve. Probably a manufacturing defect, hopefully covered under warranty.

What is the significance of the hole/slot adjacent to the failure?

 

[edison123]

Inter-turn insulation failure due to poor quality magnet wire.

Muthu

http://www.edison.co.in

 

[electricpete]

I'm not that familiar with what I'm looking at there. Right next to the fault is a plate with (for lack of better words) a cylindrical chamber embedded (tube) into it. I have to wonder if it's just a coincidence that the failure happened right next to the cylindrical chamber, or alternatively did the cylindrical chamber play some role in the failure. Some questions:
[ol 1]
[li]Is that a slot running along the cylindrical chamber on the winding side? (or is it just a black trail of soot).[/li]
[li]If it's a slot, are the edges of that slot rough?[/li]
[li]What function does this mechanical construction (cylindrical chamber and maybe slot) fulfill?[/li]
[/ol]

If it's a slot with rough edges then one obvious scenario is that the wires and the slot edge were vibrating against each other, causing abrasion of the insulation.

=====================================
(2B)+(2B)' ?

 

[Gr8blu]

Fairly classic turn-to-turn fault that (perhaps) ended up going to ground - evidence for ground fault is unclear from image.
Possible cause(s): 1) damage to strand insulation during coil manufacture might not have been enough to fault during factory testing, but certainly might have if the nonlinear (VSD) load is providing enough common-mode voltage or a high enough frequency signal. 2) simple overvoltage from nonlinear (VSD) load resulting from common mode voltage being present. 3) impact from debris damaged the strand insulation in adjacent strands.

Given the provided image, I'd be looking at one of the first two possibilities.

To electricpetes point: that cylinder is (likely) a guide for either a temperature detector lead OR the in/out to the coil itself. The edges appear a bit rough, and yes - that IS a slot in the insulated material of the collar, not a smudge of soot.

Converting energy to motion for more than half a century

 

[wcaseyharman]

I am assuming this is brushless exciter, and the stator of a brushless exciter is DC. You mention the AVR is blown - it seems to me that likely connected. Is the exciter a floating voltage or is the field a hard negative? Does the exciter have any ground detection? I’m guessing the mag wire shorted to ground and the resulting high current blew up the AVR, but that theory depends upon the grounding method of the voltage regulator, unless there’s another ground location.