Advice sought - isolation transformer inrush current limiting

[Bill Danielson]

Back to the OP, I am a Maintenance Technician in a large mfg plant, we 
have a LOT of transformers in the plant and when power is turned off an 
back on there is never any issue at all. Sounds kind of strange that 
this is going on. I understand some basics of how an inductor works, 
that there will be an initial surge until the magnetic field builds up, 
but Industrial stuff must be made to just work on power up and not blow 
a properly sized fuse ??

Bill


On 05/23/2018 10:04 AM, Karl W4KRL wrote:
>
> Jerry,
>
> My speculation is that the minuscule motion of the laminations against 
> each other transfer mechanical energy to the coating on the 
> laminations thereby warming them slightly. As they become stickier or 
> softer they do a better job of dampening the emitted sound.
>
> Karl W4KRL
>
> *From:* jerome whelan <whelanjh at gmail.com> *On Behalf Of *Jerome Whelan
> *Sent:* Tuesday, May 22, 2018 10:17 PM
> *To:* W4KRL at arrl.net
> *Cc:* Mark Whittington <markwhi at gmail.com>; Tacos <tacos at amrad.org>
> *Subject:* Re: Advice sought - isolation transformer inrush current 
> limiting
>
> Please pardon my jumping in on this issue, but I think this might be 
> an opportunity to increase my knowledge on magnetostrsiction… I have 
> observed that a large transformer, when initially energized at 
> no-load, generates a loud power-frequency sound which fades out over 
> ten to fifteen seconds…
>
> What causes the time-decaying character of the hum sound ?
>
> Jerry AB3SX
>
>
>
>     On May 22, 2018, at 14:29 PM, Karl W4KRL <W4KRL at arrl.net
>     <mailto:W4KRL at arrl.net>> wrote:
>
>     Mark,
>
>     This is due to remanent flux in the transformer core. If the first
>     half cycle of the line tries to magnetize the core in the same
>     polarity, it will saturate the core and draw high current. One
>     possible approach is to put a resistor in series with the line and
>     cut out the resistor after the transformer core resets. An
>     incandescent bulb, say 75W if you can find one, would be a good
>     resistor.
>
>     That said, try an SL22 10008 NTC.
>
>     https://www.ametherm.com/inrush-current/transformer-inrush-current.html?gclid=CjwKCAjw_47YBRBxEiwAYuKdw6_IzT-R5wYlOv0eMMWHP5owpuxpxYzNUo4YC3SoXzx-6Xj7CdVNiBoCnDsQAvD_BwE
>
>     Karl W4KRL
>
>     *From:*Tacos <tacos-bounces+karl.w4krl=gmail.com at amrad.org
>     <mailto:tacos-bounces+karl.w4krl=gmail.com at amrad.org>>*On Behalf
>     Of*Mark Whittington
>     *Sent:*Tuesday, May 22, 2018 6:57 AM
>     *To:*Tacos <tacos at amrad.org <mailto:tacos at amrad.org>>
>     *Subject:*Advice sought - isolation transformer inrush current
>     limiting
>
>     I've got a 1KW isolation transformer that usually trips the 15A
>     breaker at the breaker box when I turn it on, load or no.  I'm
>     considering installing a pair of NTC thermistors on the input side
>     of the transformer, but I've no idea how to size them or if there
>     might be a better option.
>
>     Any advice would be appreciated.
>
>     Cheers.
>
>     -Mark
>
>     _______________________________________________
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>     Tacos at amrad.org <mailto:Tacos at amrad.org>
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>
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