600 volt, 3 phase surge protection

[kwired]

Moreover I brought up this possibility to stress the fact that a SPD can be destroyed by the action of current alone without its surge energy any thing to do with it.

Doesn't there need to be energy to make current happen?

 

[T.M.Haja Sahib]

Doesn't there need to be energy to make current happen?

Yes, there need to be energy to make current happen. So what?

 

[Besoeker]

Listen, Bes. You never said any thing about the possibility of the SPD destruction by mechanical force of current until I brought it up. Don't you think it is something constructive?

It's about as constructive as the probability of it happening.
:roll:

 

[T.M.Haja Sahib]

It's about as constructive as the probability of it happening.
:roll:

Your counterargument is not sound, because it is based but on your limited experience. An engineer's way is to demonstrate by means of calculation: taking a SPD model with multiple MOV's in parallel, calculating its minimum surge current limit for its mechanical strength to withstand from design parameters, comparing with available maximum lightning current so far recorded and thus showing the probability of destruction of SPD by mechanical force of a current occurring is vanishingly small or not.

 

[Besoeker]

Yes, there need to be energy to make current happen. So what?

It appears that the opinions I have provided and supported with evidence are not mine alone.

From Wikipedia:

Hazards

While a MOV is designed to conduct significant power for very short durations (about 8 to 20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. Under normal utility voltage conditions, this is not a problem. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Application of sustained over-voltage to a MOV can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue

No mention whatsoever of them being destroyed by physical force.

And another:

Traditional MOVs are highly susceptible to damage from sustained/temporary overvoltage conditions (Fig. 1). During these overvoltage conditions, MOVs enter a partial conductive state where they absorb the associated energy ? eventually generating enough heat to force the component to rupture and initiate a short circuit condition.

http://powerelectronics.com/mag/power_thermally_protected_movs_3/

Again, no mention whatsoever of them being destroyed by physical force.

Seems that you're out on a limb on this one, Maharajah.

 

[Besoeker]

Your counterargument is not sound, because it is based but on your limited experience.

See post #105.

 

[T.M.Haja Sahib]

Anyway, see my post# 104, Bes. Perhaps the study of destruction SPD with parallel mov's is not complete till date. You may have a chance to enhance the knowledge of humanity about this particular mode of failure by following my suggestion in that post. Hope you may mention me somewhere in your report........

 

[Besoeker]

Anyway, see my post# 104, Bes. Perhaps the study of destruction SPD with parallel mov's is not complete till date. You may have a chance to enhance the knowledge of humanity about this particular mode of failure by following my suggestion in that post. Hope you may mention me somewhere in your report........

I've never seen a solid state device fail owing to mechanical force.
Singular. That's where the topic started.
You moved the goalposts to include an array of such devices to try to support your contention.
But, let?s look at a few simple numbers to see if it does.

You are no doubt conversant with the definition of the Amp?re as the constant current that will produce an attractive force of 2 ? 10^7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum.

That gives us a starting point. Let?s assume that the fault current is 10kA. We have something under that from the supply in our test bay so maybe not an unreasonable assumption. How far apart are the MOVs? Say 20mm (about ? of an inch). Chuck those numbers into the Besoeker blender and you come up with a force of 5N. With me so far?

So what is a force of 5N like? One newton gives a mass of one kg an acceleration of one m/s/s. If the MOVs weigh just 0.1 kg then acceleration would be 50m/s/s

For time, let?s take a generous 20us.

We can now apply Newton?s laws of motion. Specifically that for distance.
s = ut + ? at^2.
Initial velocity, u, is zero.
So, we get s = 0.00001mm.

I think the numbers simply don?t support your contention.

 

[T.M.Haja Sahib]

Bes, congrats for your efforts. :thumbsup:

One small problem.

As I stated elsewhere in the forum, the surge energy is very modest and so to prove on the basis of how far the MOV element would move on the expenditure of surge energy is not convincing. It requires working out of mechanical force limit on individual MOV's.

Your workout of force of 5N appears to be very much on the lower side. Care to give more details?

Thanks.

 

[Besoeker]

Bes, congrats for your efforts. :thumbsup:

I'll assume that was intended as a compliment so, thank you.

One small problem.

Two, actually.
I stated that it was fault current instead of surge current.
The force should have been 2 ? 10^-7 newton per metre of length but I did use the correct value in the calculation.

As I stated elsewhere in the forum, the surge energy is very modest and so to prove on the basis of how far the MOV element would move on the expenditure of surge energy is not convincing.

I was responding to your point:

Moreover I brought up this possibility to stress the fact that a SPD can be destroyed by the action of current alone without its surge energy any thing to do with it.

My calculation was based on current alone. The 10kA was taken as a reasonable assumption. In any case, you'd have some difficulty getting up to that level and back to zero within 20us in most circuits unless they were specifically designed for low inductance.

It requires working out of mechanical force limit on individual MOV's.

You introduced multiple units in parallel.

Your workout of force of 5N appears to be very much on the lower side.

Why? Because it doesn't fit with the assertion you have been making?
Actually, it might be too high. It's 5N per metre of length and the device isn't likely to be a metre in length.

Care to give more details?

I provided all the details required to do the calculation.

 

[mivey]

You introduced multiple units in parallel.

I think to hit the target you are going to have to lead him just a bit. Not sure what you are going to do about the wind.

 

[Besoeker]

I think to hit the target you are going to have to lead him just a bit.

I thought I had.
Evidence, calcs, experience.....but the saying involving horses and water comes to mind.....

Not sure what you are going to do about the wind.

Introduce the Beaufort scale maybe?

 

[mivey]

I thought I had.
Evidence, calcs, experience.....but the saying involving horses and water comes to mind.....

A moving target is hard enough to hit. But add in a blowing wind ...

Introduce the Beaufort scale maybe?

Sure, if there is a conversion factor for nautical vs piffle application.

 

[Besoeker]

A moving target is hard enough to hit. But add in a blowing wind ...

Of unpredictable nature....

Sure, if there is a conversion factor for nautical vs piffle application.

Yes. In Excel it's called RAND.

 

[jim dungar]

Enough,

This thread appears to have become nothing but bullying.