How is a 3-phase power grid grounded?

Question

Obviously a 3-phase (or other mult-phase) power system needs to be grounded, but I am curious as to how this is done? Where are the ground wire(s) attached and where do they end up? Does a ground wire go to the ground actually or somewhere else? It seems like if it went to the ground it could be dangerous... I don't know much about electrical power or high voltage, but I think it is interesting. So, if you can answer this please do! -Thanks!

Answer 1

Ultimately the ground is literally the ground. The earth is a good conductor and is so absolutely massive that there is no problem with grounding this way - it's not dangerous.

Of course, if a power line with 60000 volts is laying on the ground it's dangerous, because the ground near it will be live to some extent.

But, as an example, here in Australia where the mains voltage in homes is 240V, 3-phase power is 430V. It is a lot, but not when it comes to being put into the ground.

For power grid explanations, see the article.

Answer 2

If you live in a rural area you can look at the power pole by your house and typically find a ground wire coming down the pole and tied off onto a rod that is driven into the ground. The rod's potential is typically 0 volts. This ground rod is attached to the incoming neutral service wire on the power pole, the one that returns power back to the power plant. You can actually take a voltmeter and place the positive lead on the metal surface of your service panel and the neutral lead into the earth ground. You should get approximately 0 volts ac. I just finished consulting on a pool job that had a grounding leakage problem. I was getting 2 volts ac between a railing going into the pool, and the pool water. I traced it back to a major series of panel boxes in the main hotel.
It's typically old equipment and something is leaking. It is an interesting problem. Now the three phase problem is typically a Delta or Y connection and the ground actually floats. The power is used up with the system. Of course motors and such need to be grounded, but a 3 phase system floats when operating correctly.

Answer 3

There is nothing particularly complicated about the ground for 3-phase power. In the case of household current, you have a 110-volt lead (hot) and a ground lead (neutral). You need both leads to make an electrical appliance work. And you don't want the two of them (the hot and the neutral) to touch.

In the case of 3-phase, you have three different hot wires and one ground (a total of four leads). And you don't want the ground to touch any of the three hot wires.

In fact, you don't want any two of the hot wires to touch each other.
Reason: Each one is at a different voltage.
(The AVERAGE voltage for each line is the same, but because they are out of phase with each other, at any given moment they will not be at the same voltage, so connecting them will cause a short circuit.)

I think it turns out that 3-phase power is used mainly for motors in industrial applications, and that the power for the motor uses all three hot leads and does not cause any current to flow through the neutral lead. So in that case, the answer to your original question is that the system does not have a NEUTRAL lead (to carry current). However, the motor housing would be grounded (to a ground lead, not to the neutral lead; the difference is that the ground lead is not intended to carry a current, whereas the neutral lead does carry current).

Hope that helps.

Answer 4

There are primarily two systems used in 3 phase commercial/industrial applications.

Delta and Wye are terms used when wiring the primary (H1,H2,H3) and secondary (L1,L2,L3) sides of a transformer which is grounded (on the secondary side only). This is the way we can achieve higher or lower voltages (transversely currents).

Delta is a set of windings in the shape of a triangle (hence Delta) with one corner on the secondary side grounded, ex. 480v to 120/240v.

Wye, windings in the shape of Y, have a center tapped ground on the secondary side and most commonly used, ex. 480v to 120/208v.

Answer 5

buy a copper stake in a hardware store. drive it into the ground and attach the ground wire to it