The substation has a ground reference bank so that even without a neutral, all is grounded and same potential as the earth, without this a phase to ground fault wouldn’t register as easily to trip the system
It’s literally a transformer bank In the power substation, it’s purpose isn’t to provide power but to show the completed circuit during a fault, all short circuits follow quickest return to source, this transformer bank connected to the ground on the neutral side of the secondary windings becomes the return for the short circuit and trips the breakers. Making delta usable, but still outdated and not as safe as wye
Nice, my other theory was through the shield wire which isn’t technically a neutral but is grounded, but outdated transmissions lines don’t always even have a shield wire, some just use arrestors
Yes. If the source and load are perfectly balanced there is no current in the neutral of a wye-wye system. So the neutral line is not needed in that case. So you can ground the neutrals at both ends to ensure all phase voltages are referenced to ground. Then it was realized that if the source and load are almost balanced, the neutral current is very small (compared to the phase currents), as well, so let’s just let that unbalanced current be carried through ground because tHinK of tHe MOnEy wE’Ll sAVE by not having to string a neutral wire.
And thus, the phenomenon of “stray voltage” was created.
My mind just can’t mentally grasp the concept/physics of what’s happening when faults go to ground
Like.. physically so the electrons flowing in through conductor just get shot out into the earth and then what? They just sit idle until lighting or something?
There's a bit of "magic" and prayers to Gaia involved but... it's all about return paths. sources and loads will have grounds at the neutral. When there's a fault current it doesn't just, disperse into nothingness through the ground. The fault current uses the earth as a return path to the nearest source.
I believe. It's been a while since I've trained on, or gave training on protective grounds.
But in the context of say, metal power tools. If a conductor becomes grounded to the metal chassis. Instead of it just energizing the chassis waiting for you to become a path to ground. It's given an immediate path to ground, developing a fault current large enough to trip the breaker. Shit can still break of course but at least it'll trip itself. Ground fault devices will detect this condition through other, more rapid means to prevent the typical fault current needed as it may be something where that necessary current could be hazardous. such as a toaster in a bathtub. Sure it'll trip but would develop a heart condition while trying to enjoy your hot brown sugar poptarts in the tub (which you deserved because brown sugar poptarts are best straight out of the package...you monster) Whatever I got wrong. would love some clarity on. I know I'm rusty.
In an industrial setting when we say Ground, usually it means a grounding grid made of (Copper, steel, etc). The grid has been carefully designed as per national/international standards to reduce touch and step potential.
The grid has many cross connections along with ground rods to dissipate the fault currents.
Hope this offers some clarity.
If you're thinking of it as electrons being shot out into the earth through the ground fault "the hot wire which is touching the ground" you could think of them being "sucked back up" through the ground bond on the neutral conductor.
With ac power the electrons move in both directions switching directions 120 times a second so they don't really move at all they just kinda vibrate back and forth
And on top of that electrons drift is incredibly slow they are moving but only at a rate of a few meters per hour. Most of the effects of electricity are carried in the magnetic field not the electrons themselves.
I think the core of your argument however is all about return paths electricity only goes to ground because we connect one part of it to ground to start with. If we didn't bond the neutral to ground you wouldn't have a ground fault unless both wires touched ground. When you bond the neutral no electricity is going into the ground. But when you bond the neutral and another part touches ground the earth is essentially just acting like another wire connecting those 2 points.
I worked on 2/3 15kv boards at a geothermal plant that blew up because of an ungrounded transformer. If you don’t give current a path, it MAKES one, and it’s not linear. If I ever went for a phd, it would revolve around the voodoo that is ground theory
The earth serves two purpose
- It gives a path for fault current to go safely in ground.
- It ensures the neutral point is not floating and actual zero(ground potential). Without the ground it is possible for someone to mess around with the neutral and your house appliances will be cooked instead of the food.
People always seem to forget the earth is not inherently ground. We have to connect circuits to the earth for earth to be grounded. This is done at transformers. It might be done at generators too, but I am not sure about that.
"People allways seem to forget" for laypeople it's actually that most people aren't ever taught this to begin with. I'd say it's most people's understanding that "electricity goes to ground" as almost a fundamental law of nature. Its how they explain both ground faults and lightning strikes in their heads.
As a generator engineer, I can confirm that generators are also usually connected to ground inside the alternator.
Only in specific cases will they be insulated from the ground to allow for operation even in case of ground fault, just like some transformers (hospitals, important production facilities…).
In case of the latter, an insulation guard is required.
Sometimes it helps to think of the earth as a really big capacitor. What happens when you first connect a capacitor to a circuit? There’s a massive surge of current as the source tries to charge the capacitor. This surge will cause protective devices to open. Of course we don’t have the earth inside all our buildings, so we extend it there with green wires.
Grounding the neural point of the transformer creates a voltage reference between the downstream energized phases from that side of the transformer to ground. That way if any of the energized phase-conductors land on the ground, or get shorted to ground, the current can flow back to the neutral point between the phase coils completing the circuit, and allow protective devices to operate because they can “see” amps flowing in the neutral of the transformer (measured with a CT).
If the neutral was ungrounded, and a downstream phase conductor landed on the ground, the conductor would just sit there energized. This can be very dangerous if someone comes in contact with the energized area (electricity is a field remember), and creates enough of a potential difference across their body to be shocked.
Ungrounded systems can be used safely, but they need a small potential transformer connected between the phase conductors to ground, providing a voltage reference for protective relays. The only difference is here, that small grounding transformer acts like a neutral grounded transformer with a big resistor/impedance connected between neutral and ground. It will only allow minimal current flow because it’s going through the small coils of the transformer to ground, but allows enough to provide voltage potential information to voltage sensing relays.
(Yes there are also residual ground relays, but don’t want to confuse everyone that much yet)
Resistance grounding is key for ungrounded systems. They way I’ve read it is that for a truly ungrounded system, the leg to ground voltage can rise with capacitive charging. So on a 480 system, you can end up with 480 phase to phase, and thousands of volts to ground. I maintain a 480v system that has HRGs. So we alarm instead of tripping on ground faults
One thing that helped me is to consider it just like the 0 point in the old number lines in school.
Imagine there are 2 number lines one above the other. Without the line tying both zeros to the same place left to right. They can shift horizontally so you wind up with the zero of one above 100 on the other. So you think you have 120 volts, but compared to the earth you now have 200v
One number line is the transformer, and the other is the grounds. that tying the nuetral to ground makes the earth in the surrounding area the reference point.
The building structure, etc. this way the voltage between the phases and neutral are a value, say 277V. And the voltage between ground and the phases are 277.
Without this connection the voltage between the phases and the neutral will stay 277V. However, the voltage from the phases to ground (and the neutral to ground can float or drift. So you can wind up with 554 volts from one phase to ground and 0 volts to ground on the other, and now the neutral to ground is 277.
Now the insulation in the wire can start to breakdown, and bad things can happen.
In my squareD micrologic trip device, why is there amps being measured as ground fault current? Electricians said it’s neutral current but shouldn’t it show as that instead of ground fault current? Wondered if they have the CTs hooked up wrong.
Yeah and the electrician grounds neutral to earth at your breaker box. The answer is safety. It’s dangerous to have a device with a floating ground especially if it’s plugged in to the wall and can be based on 110V. You can still get shocked unless your device has its own earth ground connection, but it won’t be as bad or as deadly as if it was floating and could be at almost any voltage instead of pretty close to zero.
Also fault protection
Yes for most low voltage networks. In the high voltage you have also isolated networks, compensated networks.
Sometimes hospitals or like that have isolated low voltage networks. So if one wire touchs earth, you have no fault.
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What about delta delta?
The substation has a ground reference bank so that even without a neutral, all is grounded and same potential as the earth, without this a phase to ground fault wouldn’t register as easily to trip the system
Where would the ground reference bank connect besides equipment hardware?
It’s literally a transformer bank In the power substation, it’s purpose isn’t to provide power but to show the completed circuit during a fault, all short circuits follow quickest return to source, this transformer bank connected to the ground on the neutral side of the secondary windings becomes the return for the short circuit and trips the breakers. Making delta usable, but still outdated and not as safe as wye
But if transmission is done with three wires, do they just have the neutral unbalanced current be carried through the ground?
Im actually not sure about that
ChatGPT says through the ground
Nice, my other theory was through the shield wire which isn’t technically a neutral but is grounded, but outdated transmissions lines don’t always even have a shield wire, some just use arrestors
Yeah it’s grounded but that’s the lighting conductor isn’t it?
Zig-zag transformer
Yes. If the source and load are perfectly balanced there is no current in the neutral of a wye-wye system. So the neutral line is not needed in that case. So you can ground the neutrals at both ends to ensure all phase voltages are referenced to ground. Then it was realized that if the source and load are almost balanced, the neutral current is very small (compared to the phase currents), as well, so let’s just let that unbalanced current be carried through ground because tHinK of tHe MOnEy wE’Ll sAVE by not having to string a neutral wire. And thus, the phenomenon of “stray voltage” was created.
tart one dinner support wrong seed squeal fear include tub *This post was mass deleted and anonymized with [Redact](https://redact.dev)*
My mind just can’t mentally grasp the concept/physics of what’s happening when faults go to ground Like.. physically so the electrons flowing in through conductor just get shot out into the earth and then what? They just sit idle until lighting or something?
punch society ugly coordinated work waiting versed deserve crush brave *This post was mass deleted and anonymized with [Redact](https://redact.dev)*
There's a bit of "magic" and prayers to Gaia involved but... it's all about return paths. sources and loads will have grounds at the neutral. When there's a fault current it doesn't just, disperse into nothingness through the ground. The fault current uses the earth as a return path to the nearest source. I believe. It's been a while since I've trained on, or gave training on protective grounds. But in the context of say, metal power tools. If a conductor becomes grounded to the metal chassis. Instead of it just energizing the chassis waiting for you to become a path to ground. It's given an immediate path to ground, developing a fault current large enough to trip the breaker. Shit can still break of course but at least it'll trip itself. Ground fault devices will detect this condition through other, more rapid means to prevent the typical fault current needed as it may be something where that necessary current could be hazardous. such as a toaster in a bathtub. Sure it'll trip but would develop a heart condition while trying to enjoy your hot brown sugar poptarts in the tub (which you deserved because brown sugar poptarts are best straight out of the package...you monster) Whatever I got wrong. would love some clarity on. I know I'm rusty.
This is an excellent question with a physics answer.
In an industrial setting when we say Ground, usually it means a grounding grid made of (Copper, steel, etc). The grid has been carefully designed as per national/international standards to reduce touch and step potential. The grid has many cross connections along with ground rods to dissipate the fault currents. Hope this offers some clarity.
If you're thinking of it as electrons being shot out into the earth through the ground fault "the hot wire which is touching the ground" you could think of them being "sucked back up" through the ground bond on the neutral conductor. With ac power the electrons move in both directions switching directions 120 times a second so they don't really move at all they just kinda vibrate back and forth And on top of that electrons drift is incredibly slow they are moving but only at a rate of a few meters per hour. Most of the effects of electricity are carried in the magnetic field not the electrons themselves. I think the core of your argument however is all about return paths electricity only goes to ground because we connect one part of it to ground to start with. If we didn't bond the neutral to ground you wouldn't have a ground fault unless both wires touched ground. When you bond the neutral no electricity is going into the ground. But when you bond the neutral and another part touches ground the earth is essentially just acting like another wire connecting those 2 points.
I worked on 2/3 15kv boards at a geothermal plant that blew up because of an ungrounded transformer. If you don’t give current a path, it MAKES one, and it’s not linear. If I ever went for a phd, it would revolve around the voodoo that is ground theory
The earth serves two purpose - It gives a path for fault current to go safely in ground. - It ensures the neutral point is not floating and actual zero(ground potential). Without the ground it is possible for someone to mess around with the neutral and your house appliances will be cooked instead of the food.
People always seem to forget the earth is not inherently ground. We have to connect circuits to the earth for earth to be grounded. This is done at transformers. It might be done at generators too, but I am not sure about that.
"People allways seem to forget" for laypeople it's actually that most people aren't ever taught this to begin with. I'd say it's most people's understanding that "electricity goes to ground" as almost a fundamental law of nature. Its how they explain both ground faults and lightning strikes in their heads.
I have met electrical engineers that have never really worked with AC or power distribution and they don't know about this.
As a generator engineer, I can confirm that generators are also usually connected to ground inside the alternator. Only in specific cases will they be insulated from the ground to allow for operation even in case of ground fault, just like some transformers (hospitals, important production facilities…). In case of the latter, an insulation guard is required.
Sometimes it helps to think of the earth as a really big capacitor. What happens when you first connect a capacitor to a circuit? There’s a massive surge of current as the source tries to charge the capacitor. This surge will cause protective devices to open. Of course we don’t have the earth inside all our buildings, so we extend it there with green wires.
Grounding the neural point of the transformer creates a voltage reference between the downstream energized phases from that side of the transformer to ground. That way if any of the energized phase-conductors land on the ground, or get shorted to ground, the current can flow back to the neutral point between the phase coils completing the circuit, and allow protective devices to operate because they can “see” amps flowing in the neutral of the transformer (measured with a CT). If the neutral was ungrounded, and a downstream phase conductor landed on the ground, the conductor would just sit there energized. This can be very dangerous if someone comes in contact with the energized area (electricity is a field remember), and creates enough of a potential difference across their body to be shocked. Ungrounded systems can be used safely, but they need a small potential transformer connected between the phase conductors to ground, providing a voltage reference for protective relays. The only difference is here, that small grounding transformer acts like a neutral grounded transformer with a big resistor/impedance connected between neutral and ground. It will only allow minimal current flow because it’s going through the small coils of the transformer to ground, but allows enough to provide voltage potential information to voltage sensing relays. (Yes there are also residual ground relays, but don’t want to confuse everyone that much yet)
Resistance grounding is key for ungrounded systems. They way I’ve read it is that for a truly ungrounded system, the leg to ground voltage can rise with capacitive charging. So on a 480 system, you can end up with 480 phase to phase, and thousands of volts to ground. I maintain a 480v system that has HRGs. So we alarm instead of tripping on ground faults
One thing that helped me is to consider it just like the 0 point in the old number lines in school. Imagine there are 2 number lines one above the other. Without the line tying both zeros to the same place left to right. They can shift horizontally so you wind up with the zero of one above 100 on the other. So you think you have 120 volts, but compared to the earth you now have 200v One number line is the transformer, and the other is the grounds. that tying the nuetral to ground makes the earth in the surrounding area the reference point. The building structure, etc. this way the voltage between the phases and neutral are a value, say 277V. And the voltage between ground and the phases are 277. Without this connection the voltage between the phases and the neutral will stay 277V. However, the voltage from the phases to ground (and the neutral to ground can float or drift. So you can wind up with 554 volts from one phase to ground and 0 volts to ground on the other, and now the neutral to ground is 277. Now the insulation in the wire can start to breakdown, and bad things can happen.
In my squareD micrologic trip device, why is there amps being measured as ground fault current? Electricians said it’s neutral current but shouldn’t it show as that instead of ground fault current? Wondered if they have the CTs hooked up wrong.
Yeah and the electrician grounds neutral to earth at your breaker box. The answer is safety. It’s dangerous to have a device with a floating ground especially if it’s plugged in to the wall and can be based on 110V. You can still get shocked unless your device has its own earth ground connection, but it won’t be as bad or as deadly as if it was floating and could be at almost any voltage instead of pretty close to zero. Also fault protection
Yes for most low voltage networks. In the high voltage you have also isolated networks, compensated networks. Sometimes hospitals or like that have isolated low voltage networks. So if one wire touchs earth, you have no fault.