lightning rods vs surge suppressor

[hurk27]

I agree, this is true at the point of service, however consider , the protection downstream, for eg., a submersible pump installed 200ft below grade. The casing of the pump would be at a lower grounding impedance than the service ground. Since service grounding impedance cannot change during a fast rising surge due to inductance, the potential difference between the winding, which is reference to the system ground, and the grounded motor frame, would become enough to cause an insulation failure. Thus L-G, L-G-L & N-G connection of SPD is very crucial .

If lightning takes the path to the well casing after striking the house or service, it will to some extent treat the conductors running to this well as a single grounding conductor, while SPDs might give some relief between line and grounded conductor which could limit some damage, I highly doubt that it would protect a cable feeding this well, I have seen a few hits like this and there was nothing left of the UF feeding the well, along with the control box for it, and also only a direct strike will be trying to return to Earth as I have said before, which I don't see a MOV withstanding a direct strike, Its wishful thinking if you do.

Now if the circuit was run in a metallic raceway and this raceway was bonded to this casing, you might have a better chance, around here most well casings are PVC plastic,so very few motors are spared, even with SPD's

 

[LISHAJI]

If there is a surge from the utility, the SPD shorts from line to line and sends it back to the utility, or from line to neutral and sends it back.

I have reservations to accept this statement, because surges are transients classified by IEEE C62.41.2 for testing purposes a wave of 10 kA (8/20 μs). This is a fast rising and subsiding with a front of 8μs and tail of 20 μs. If we consider this wave going back to utility through the neutral, then the voltage of the neutral won't be any different than the hot conductor, with reference to earth, due to the high di/dt and it would be flashing over much worser than the hot conductor!!

The surge does goes back to the where it came from and that is called reflection of the wave and not due to surge arrestor.

 

[LISHAJI]

SPD requires ground to save itself and the equipment, other wise they self distruct to protect the equipment. Thus we find more SPD failures because they were not installed properly.

Here is one manufacture's test Data which makes it self evident

http://www.efinet.com/documents/datasheets/IEEE_Testing_9990-0200B.pdf

or refer to IEEE c62.41.2-2002 Table 5, which compares, neutral not grounded at service and neutral grounded at service, and the resulting SPD effectiveness.

 

[LISHAJI]

Here is one manufacture's test Data which makes it self evident

http://www.efinet.com/documents/datasheets/IEEE_Testing_9990-0200B.pdf

If you look at the test data, the let through voltage in not even tested L-L below 240kA. Protection is required between ungrounded and grounded conductor!!

 

[T.M.Haja Sahib]

The surge does goes back to the where it came from and that is called reflection of the wave and not due to surge arrestor.

The surge arrester causes the reflection.
And what about the transmitted surge wave?

 

[LISHAJI]

The surge arrester causes the reflection.
And what about the transmitted surge wave?

The transmitted surge wave diffuses to ground potential!! And system frequency voltage is restored!!

Think of what happens if you abruptly shut a domestic water tap. Your static water pressure might be a couple of bars, nothing too exciting, but get the water flowing and if you stop it abruptly you get loud water hammering, and sometimes actual damage to plumbing.Such effects have been known to burst piping. So lightning arrestor is a kind of safety valve to equalize the pressure, by shedding it to the ground reference, wrt to which it has risen.

 

[T.M.Haja Sahib]

The transmitted surge wave diffuses to ground potential!! And system frequency voltage is restored!!

Think of what happens if you abruptly shut a domestic water tap. Your static water pressure might be a couple of bars, nothing too exciting, but get the water flowing and if you stop it abruptly you get loud water hammering, and sometimes actual damage to plumbing.Such effects have been known to burst piping. So lightning arrestor is a kind of safety valve to equalize the pressure, by shedding it to the ground reference, wrt to which it has risen.

If you are pleased,why not put some calculations here? For that purpose let me suggest you a problem.A dry type transformer is to be protected against a surge of 10kA.Its surge withstamd capability is say 5kA only.What is the rating of the surge arrester and at what distance should it be placed from the transformer?

 

[LISHAJI]

If you are pleased,why not put some calculations here? For that purpose let me suggest you a problem.A dry type transformer is to be protected against a surge of 10kA.Its surge withstamd capability is say 5kA only.What is the rating of the surge arrester and at what distance should it be placed from the transformer?

If you have to please me you have to send me some Greenbacks!!. Anyway to completely solve your situation, you haven't given complete specification of your transformer. In general I would protect it with a type 1 SPD. The lead distance from transformer terminal should be as short as possible and preferrabley twisted to get a better clamping voltage. Hope that helps!!

 

[LISHAJI]

DISPERSION OF LIGHTNING CURRENT AFTER A DIRECT FLASH TO A BUILDING

DISPERSION OF LIGHTNING CURRENT AFTER A DIRECT FLASH TO A BUILDING

http://www.eeel.nist.gov/817/pubs/spd-anthology/files/Dispersion.pdf

 

[T.M.Haja Sahib]

If you have to please me you have to send me some Greenbacks!!. Anyway to completely solve your situation, you haven't given complete specification of your transformer. In general I would protect it with a type 1 SPD. The lead distance from transformer terminal should be as short as possible and preferrabley twisted to get a better clamping voltage. Hope that helps!!

I have long forgotten the calculations and want to brush up my memory.So I request you again to calculate assuming any parameters you require.Sure,you will be presented Greenbacks,when we meet in person.

 

[LISHAJI]

I have long forgotten the calculations and want to brush up my memory.So I request you again to calculate assuming any parameters you require.

Isn't this against the policy of this forum to educate some DIY!!
Anyway, I would say designing SPD is not simple as that. There are various parameters that goes with its design. Equipment current surge withstand is irrelevant, as most devices can withstand ordinary surges 500%, its the voltage withstand of the devices that is important. Another thing to see what kind of protection is upstream of it and downstream of it, so that you can design an economical SPD. This would give the wattage rating of your SPD. Next step is to calculate VPR(voltage protection rating). The length of the ground connection, for example, a 10 kA impulse, rising in 3 μs, would produce a voltage drop of ~10 kV in a 10 foot grounding wire, which would add to the limiting voltage of the protector. So a protector with a nominal 400V limiting voltage would actually be limiting to (400 V + 10,000 V) = 10.4kV. Is your device rated to with stand 10.4 kV?? what are the flash points?? Hope that would brush it up!!