Re: Z-Machine Sparkage - Substation Fault

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <teslalist-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Hi Godfrey,

Jim and Dave have already provided some excellent information on the 
internal structure and operation of expulsion fuses.

The loud humming sound is most likely coming from 120 Hz vibrations of the 
windings as tremendous repulsion forces act between the primary and 
secondary under fault conditions (Lenz's Law). To combat these forces, 
power transformer manufacturers use special interleaved winding techniques 
that partially cancel the forces (at least for inner winding sections). A 
sustained low impedance short between 2 or more phases (called a "bolted 
fault") can easily bend heavy bus bars and windings like pretzels. Under 
fault conditions a low impedance power transformer driven from a low 
impedance source can create forces which can literally tear it apart. 
Inductive reactance is purposely added to help protect the transformer and 
upstream equipment from this case.

BTW, the cooking transformer in this substation actually held together 
pretty well... at least for a while.  :^)

Best regards,

-- Bert --
-- 
--------------------------------------------------
Out-of-Print Physics and Engineering Books and
coins shrunk by ultrastrong electromagnetic fields!
Stoneridge Engineering: http://www.teslamania-dot-com
--------------------------------------------------

Tesla list wrote:
>Original poster: "Godfrey Loudner by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <ggreen-at-gwtc-dot-net>
>
>Do these expulsion fuses have high explosive charges inside to blow out
>arcs? Was that loud humming sound made by bussing transformer laminations?
>Godfrey Loudner
>  >I'm going to show at an electrical
>  > safety training class at work, just to illustrate how bad a >high power
>fault
>
>.