Outage on distribution circuits due to high humidity 1

[MEG1122]

We recently had few distribution circuits tripped due to very humid weather conditions. Our initial thoughts were air pollutant combined with high humidity, reduced the creepage distance on the insulators which led to line to ground flashovers. However, we found few blown fuses along these lines aswell, which makes me think humid weather conditions may not be the root cause. Please share your thoughts./

 

[RRaghunath]

"air pollutant combined with high humidity, reduced the creepage distance on the insulators which led to line to ground flashovers" - I too think is the reason for trips as well as blown fuses.
Distribution feeders are most susceptible to pollution related as well as vegetation related trips.

 

[MEG1122]

What I am bit confused on how would line to ground flashover cause overcurrent on phase conductors resulting in blown fuses and in some cases blow surge arresters?

 

[cranky108]

In our case, we have this in the Spring, after the highway department has placed MgCl on the highways several times.
Also the same thing along the railroad from coal dust.

 

[davidbeach]

The flashover is a phase-ground fault, all of the current comes from the faulted phase. The fault is only interrupted when the fuse blows or the breaker trips.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[RRaghunath]

Single Line to ground (SLG) fault current is lower if the earth loop impedance happens to be high.
In case of bolted fault close to the source the SLG fault current can actually be more than the three phase fault current. That explains how the SLG flashover can cause fuse blowing or relay operation I suppose.
When it comes to Surge arrester (SA) damage, it is well known that the voltage (to ground) of unfaulted phases goes up during an SLG fault.
This voltage can be a max of 1.4pu in case of Effectively grounded system and can even reach 1.7pu incase of non-effectively grounded system.
Depending on
* how frequent are such faults,
* how slow is the protection in clearing the fault and
* what is the specification of SA
the SA can fail during the SLG fault

 

[Palletjack]

What types of pollutants are in the area?
“Very humid” conditions only shouldn’t blow fuses.
They don’t blow when it rains I’m assuming? The rain washes the pollutants away.

 

[FacEngrPE]

Fog bowl insulators were developed to combat insulator salt contamination near the Atlantic ocean beachfront. They are not a cure all, but did reduce the incidence of poll top fires.
Dry Band Arcing Across Wet Porcelain Fog Bowl Insulator

https://youtu.be/zHxqRPpTZFE

https://youtu.be/cLWo3bgzLL4

 

[cranky108]

Not just with rain, but also with fog, and drizzle. Even seen irrigation sprays on lines.

 

[TugboatEng]

Once a pole top fire occurs the flames are electrically conductive which could cause the short circuit fault that blows the fuses.

We are about to enter pole fire season in my county. We typically get 20-30 during the first rain.

 

[cranky108]

We have that in Spring, after the MgCl quits being sprayed.