Re: MOVs and surge suppressors

On Aug 27, 10:13 pm, ehsjr <eh...@xxxxxxxxxxxxxxxx> wrote:
Absorbing surge energy is the only way an MOV can work.
It cannot provide protection without absorbing surge energy.
That does not mean it absorbs the entire surge energy.
Where does the surge energy go? Some is absorbed and
dissipated in the source path, some in the MOV and some
in the return path.

This is a point w_tom has missed in the past when he insists
that point of use MOV's don't absorb surge energy.

w_tom never said "MOVs do not absorb energy". Even wire absorbs
energy - which is what I post everytime in response to ehsjr's
intentional misquotes. What are functions of an MOV and of wire?
Both are shunt mode devices. Both operate by shunting (diverting,
connecting, clamping, conducting) electrical current (and energy)
elsewhere. Both absorb energy when performing their job. But neither
function is to absorb all energy - as ehsjr repeatedly claimed.

If we increase MOV joules, then MOV absorbs more energy? Of course
not. If we increase the gauge of wire, then it absorbs more energy?
No. In both cases: as MOV joules and wire gauge increase, then the
device absorbs less energy - because that is what we want it to do.
The function of wire and MOVs: absorb less energy and shunt more
energy.

If MOVs are grossly undersized, then absorbed surge energy increases
massively. That unacceptable operation causes an MOV to vaporize. A
vaporized MOV exceed manufacturer acceptable ratings. Undersized
protectors - too few joules - can also create these scary pictures:
http://www.hanford.gov/rl/?page=556&parent=554
http://www.westwhitelandfire.com/Articles/Surge%20Protectors.pdf
http://www.ddxg.net/old/surge_protectors.htm
http://www.zerosurge.com/HTML/movs.html
http://tinyurl.com/3x73ol or
http://www.esdjournal.com/techpapr/Pharr/INVESTIGATING%20SURGE%20SUPPRESSOR%20FIRES.doc

When too much current passes through an MOV, then its voltage
increases. That unacceptable voltage increase is when an MOV is
grossly undersized - has too few joules. We increase MOV joules so
that an MOV does not absorb more energy; just as we increase wire
diameter.

From manufacturer data ***: An MOV for 120 volt operation rated
at 25 joules (241KD09 is an 11 mm MOV disk) see voltage climb quickly
past 800 volts during a 2500 amp surge because it is undersized - too
few joules. That peak 2 million watt surge dissipated in that MOV
means its life expectancy is 1 surge (does not vaporize). If we
increase to a 72 joules MOV (241KD18 is a 22 mm disk)). Then a 2500
amp surge creates an MOV voltage of 550; only 1.4 million watts
dissipated in that MOV. Larger MOV means increased life expectancy
and less energy absorbed by the MOV. Better protectors (more joules)
absorb less energy.

What happens if we use five 72 joule MOVs? 110 amps through each
MOV means each MOV voltage is 320 volts - 35,000 watts per MOV or
0.175 million watts total. Increasing from 25 joules to 360 joules
means MOV absorbs 11.5 times less energy. Meanwhile, the 360 joule
protector is now rated for about 3000 surges. Increases joules also
means life expectancy increases exponentially.

Why do some foolishly claim a protector is only for one surge? Why
did a plug-in protector manufacturer charge so much for so few joules?

When joules increase, MOV absorbs less energy AND MOV life
expectancy increases massively. The purpose of an MOV is not to
absorb 'more' surge as ehsjr claimed. More joules means the MOV
absorbs 'less' energy AND lasts longer - just like increasing wire
size.

ehsjr and this poster have argued this for maybe seven years. ehsjr
insisted MOVs provide protection by absorbing the entire surge. MOVs
do not. Is ehsjr finally backing off that claim?

MOVs are shunt mode devices. Like wires, MOVs are not perfect
conductors; absorb a minority of a surge. Whereas that large MOV
might dissipate 1.4 million peak watts, a same surge may also
dissipate 60 or 100 million peak watts into earth. What makes an MOV
effective? Earth ground is the protection. Earth ground is where
maybe 40 or 70 times more energy is dissipated.

A protector without earth ground means no effective protection.
Earth is where the brunt of a surge energy is absorbed; not inside an
MOV as ehsjr once repeatedly claimed.

What makes an MOV effective? MOV resistance drops so that a surge
is shunted to and dissipated by earth ground. Demonstrated above is
how the 72 joule MOV absorbs 30% less energy compared to a 25 joule
MOV. As MOV joules increase, then absorbed MOV energy decreases.

Where is most all surge energy dissipated? Not inside an MOV. Above
numbers make that obvious. Effective protection means most surge
energy is dissipated in earth. But since MOVs are not perfect, then
MOVs (like wires) absorb some of that energy. I was posting this to
ehsjr seven years ago. ehsjr still misrepresents what w_tom has
posted.

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