SINGLE POINT GROUNDING - Starts at the Sub Stations

[mtnelect]

My purpose was to "Shake Up" our understanding of the principles of grounding ...

 

[retirede]

My purpose was to "Shake Up" our understanding of the principles of grounding ...

It’s not working for me.

 

[CoolWill]

I don't know much about distribution in general, but I read in a really old book from 1922 that the long distance lines were grounded because otherwise huge charges were building up in the system to the point of large arcs being thrown off generator terminals, even some mechanics at central stations being zapped. Insulation was failing prematurely due to the huge voltages. Apparently there is a lot of field potential spread across the planet that you only notice over long distances. The brand new transmission lines of the time were long enough to stretch across areas of varying potential and charge could build up. The solution was to ground the system periodically along its route. If that is indeed true, we may not have much choice if we are to have an electrified world

 

[kwired]

I'll guarantee that most utilities are more concerned with MAKING MONEY and keeping just inside the reg's than anything else, including "stray currents". (Investor-owned will act differently than publicly or customer owned.)

Where's the business case for a massive renovation of the transmission and distribution systems? And I don't see this sort of change as a reliability enhancement, if it is, how?

Have we heard the engineers who design and maintain these systems chime in about what such a massive change would entail and improve (other than making a lot of work and enriching the copper companies)?

Heck, I'd just like to hear about where and how often the use of MGN causes actual, not perceived, problems. As mentioned above, dairy farms, around some bodies of water, inc pools, but how does that compare to the rest of the service area? Does it make sense to move away from MGN in specific areas or everywhere? (If a county has one lake with one dock and no livestock farms, how much sense does it make to re-engineer the entire distribution system for that county?)

You are correct about differences between investor owned and public owned utilities. We are all public owned throughout this state, and most are very good about focusing on performance of the system and do perform a lot of preventative maintenance instead of just waiting for some things to fail before fixing them. They also do project future needs as best as possible and try to have infrastructure to handle those needs when needed vs scrambling to be able to handle those needs after the need has arrived.

As far as the occasional livestock farm that may encounter stray voltage issues that are deemed to be coming from the utility side on the MGN, there is things like Ronk Blocker that can be installed to help with those problems as well. It goes between primary and secondary neutral to block stray voltage coming from primary. I'm not really certain exactly how it works but it says in the link I provided "The device operates directly on the principle of magnetic saturation and does not depend on external controls or internal logic signals; therefore, it reacts instantaneously, providing immediate, continuous protection at all times".

 

[kwired]

I think we should transition to all loads being line to line. Over time the neutral load fades away.

That helps with on site issues but won't stop rise in voltage on grounded conductor because of voltage drop on primary neutral.

IMO in places like dairy farms it is better to only use line to line voltages as much as possible which does reduce any stray voltages from on site loading. Things have changed on the typical dairy farm over the past 30 years though. Long gone is majority of small herd operators, those that maybe only milk 50 to 100 head of cows max. Now it is 500 to 1000 at a minimum and the place is more of an industrial site when it comes to electric and mechanical installation. You don't have some 50 to 100 square foot room with the 100 amp single phase service in it and a 7.5 or 10 HP vacuum pump being the major electric/mechanical items in that room. You have a over 1000 square feet of electric / mechanical room with who knows how many amps (probably 400-600 minimum though) @ 480/277 volts for incoming service, at least two vacuum pumps though only one may run at a time you need at least one other as a backup, multiple air compressors again at least one for a backup, service may even be switchboard with MCC incorporated in there as well.

 

[kwired]

I don't know much about distribution in general, but I read in a really old book from 1922 that the long distance lines were grounded because otherwise huge charges were building up in the system to the point of large arcs being thrown off generator terminals, even some mechanics at central stations being zapped. Insulation was failing prematurely due to the huge voltages. Apparently there is a lot of field potential spread across the planet that you only notice over long distances. The brand new transmission lines of the time were long enough to stretch across areas of varying potential and charge could build up. The solution was to ground the system periodically along its route. If that is indeed true, we may not have much choice if we are to have an electrified world

Capacitance is a thing.

Still causes problems particularly with higher voltage transmission lines and is reason you seldom see a lower voltage distribution line running parallel in closer proximity to those higher voltage transmission lines. Under ~100kV transmission lines often have lower volt distribution running at lower levels on same poles but for over 100kV those lines have nothing else on the pole and local distribution lines are a certain distance away when running parallel to them. I still ran into issues though when the local distribution was on one side of a road and a 230 kV line was on opposite side of the road. I had like 8 or 9 volts from recollection between service neutral and earth, no load on the service at that time. It was a new service and even newly reconstructed distribution line as originally there wasn't three phase to where this site was. Asked POCO to make sure everything was ok with their line. After checking things out they said everything was good and that it was coming from that transmission line. Been over a year and no complaints yet. I'm thinking about going back and seeing if it can drive any load or if that will drop the voltage as soon as you put load on it. There was no shocking when touching equipment. I only noticed this because when I connected the grounded service conductor it sparked when making contact with the lug - the grounding electrode was already in place.

 

[electrofelon]

Anyway, lots of people, maybe even the vast majority, never have problems with/from the utility MGN system and don't have to deal with "all of this 'Stray Current' floating around everywhere"...

Yeah. I grew up on it, and I'm kinda used to it. Plus, I have never encountered a problem with it.

Yeah, I know this issue seems to really keep the OP up at night, but how many people have actually had a problem resulting from a MGM distribution system???

 

[LarryFine]

Yeah, I know this issue seems to really keep the OP up at night, but how many people have actually had a problem resulting from a MGM distribution system???

Technically speaking, it's "none of our business" what the POCO does before the power hits the service.

We are presented with a grounded circuit conductor that establishes the zero-volts-to-ground point.

 

[topgone]

unless everyone used ground fault protective devices on pretty much everything you would still have current on the grounding conductors any time someone didn't "follow the rules" or had unintended current on the grounding conductor.

You would still have bonding at every separately derived system and chances of stray currents should something go wrong.

I still think things like swimming pools should require equipotential bonding even if such distribution were utilized, problems won't be as bad but still is possible to have voltage gradients within the pool.

NEC has been there for an eternity. Other countries developed their own and also think their system works. We have been following NEC and we think we're covered. What's new?

 

[ramsy]

I only noticed this because when I connected the grounded service conductor it sparked when making contact with the lug - the grounding electrode was already in place.

Can that be transformed for a free, electric fence?

Or un-balanced loads, if grounded conductor is not first make first break.

 

[Sunny_92]

I spent a summer working as a distribution reliability engineering intern and did a number of stray voltage investigations during that time. I really only saw issues with stray voltage on long single phase lines. Almost all of the stray voltage issues I encountered were due to issues on the customer's system. I believe only one of my investigations resulted in the recommendation to install a neutral isolator at the service transformer.

 

[kwired]

Technically speaking, it's "none of our business" what the POCO does before the power hits the service.

We are presented with a grounded circuit conductor that establishes the zero-volts-to-ground point.

Except there is almost always a small amount of voltage to ground because of voltage drop on the grounded conductor.

I've had service calls because of it for stray voltages in bathtubs/showers. Two times it was water pipes were bonded to electric service but metallic drain piping wasn't bonded and at earth potential. Another time was a shower in a basement, I think drain piping was new enough it likely was plastic but the floor drain embedded in concrete floor was metallic and providing enough conductivity to earth to cause problems. I think we ended up isolating that shower with a section of non metallic water piping to solve that issue.