Re (2): UPS with earth leakage device.
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From: david on 10 Jan 2010 21:25 On Fri, 08 Jan 2010 20:12:39 -0500, GangGreene rearranged some electrons to say: > Guys/Gals Please > > One question.... > > How many wires from an electical substation to the trasformer on the > pole? > > Answer One. > > There is no neutral. > The power is returned through the earth, through a ground system. Clearly you have no knowledge how an electric disribtion system works. In a delta-connected system, there is no neutral. In a wye-connected system the neutral point is the common point where all three phases are tied together. If the three phases are balanced, there will be no net current and thus no voltage at the neutral point. Since the phases are rarely perfectly balanced, there is usually some voltage at the neutral point. A typical premises distribution transformer in the US will step down one single phase of a three-phase delta (or wye) transformer primary to 240V across two lines. The neutral is a center tap from the secondary winding, and is bonded to earth ground in the service entrance panel, per the US National Electric Code. If your house (or business) has 3-phase power, it is usually a 4-wire (wye) system. The secondary side of the transformer is connected as a wye, which means the neutral is the common point of the three windings. Per US code, the neutral must be bonded to earth ground at the service entrance.
From: GangGreene on 11 Jan 2010 09:32 david wrote: > On Fri, 08 Jan 2010 20:12:39 -0500, GangGreene rearranged some electrons > to say: > > >> Guys/Gals Please >> >> One question.... >> >> How many wires from an electrical substation to the transformer on the >> pole? >> >> Answer One. >> >> There is no neutral. >> The power is returned through the earth, through a ground system. > > Clearly you have no knowledge how an electric distribution system works. Ah yes you are correct, that is why I have been a controls engineer for 25 years at a very large retail company. > > In a delta-connected system, there is no neutral. Not so, you could have a corner grounded delta. One could also have a 4 wire delta system. > In a wye-connected system the neutral point is the common point where all > three phases are tied together. There is a common point but I don't it's required to be connected to ground. I will have to look it up in my NEC book. You also don't need to use the common point wire. It is a common point but really not a neutral. Remember a neutral is only a reference point, which is useally tied to ground. I have seen corner grounded wye installations. Now what? > If the three phases are balanced, there > will be no net > current and thus no voltage at the neutral point. Since the phases are > rarely perfectly balanced, there is usually some voltage at the neutral > point. Both reactively and resistance balanced of course. Power factors being involved. > > A typical premises distribution transformer in the US will step down one > single phase of a three-phase delta (or wye) transformer primary to 240V > across two lines. The neutral is a center tap from the secondary > winding, and is bonded to earth ground in the service entrance panel, per > the US National Electric Code. It is not a neutral at the pole, just a simple center tapped xfmr with both ends out of phase with respect to the center tap point (ie the reference point). It only becomes a neutral at the service panel. > > If your house (or business) has 3-phase power, it is usually a 4-wire > (wye) system. The secondary side of the transformer is connected as a > wye, which means the neutral is the common point of the three windings. Doesn't have to be 4 wire could be 3 wire wye connection. > Per US code, the neutral must be bonded to earth ground at the service > entrance. Now what about 13.2 KV service to a building? Care to comment on that? Do you know what a switch gear is?
From: Moe Trin on 11 Jan 2010 15:01 On Sun, 10 Jan 2010, in the Usenet newsgroup comp.os.linux.hardware, in article <4b4a5884$0$278$14726298(a)news.sunsite.dk>, ArameFarpado wrote: >Bit Twister escreveu: >>ArameFarpado wrote: [Bit Twister wrote:] >>>> Once the current gets high enough in R2's brain/heart death occurs. Well, let's just say that significant problems occur with R2, whether it be a bird, cow, human, or some electronics. >>> for that to work the way you say, the conductor must be highly >>> damage right under the bird/man feet. No. >> Absolutely not. Under normal conditions no conductor is resistance >> free Oh, like you mean the ground between the {bird|cow|person}s legs? Yeah - had a problem like that happen. A lightning strike hit the ground several hundred {feet|meters} away from an aircraft landing guidance transmitter. The transmitter, transmitting antenna, and associated electronics in one building with _three_ 25 foot/7.6 meter long ground rods (two for lightning rods, one for the power/electronics) and the "monitor" antenna on a stub mast 100 foot/30 meters away with two more of those long ground rods (one for the mast, one for the electronics). The distance from the strike to the two sites was not equal, and we had differential ground voltages because of it. The monitor (video) signals were protected by lightning arrestors (spark gap and Surgistors) at BOTH ends of the wire. The protection apparently worked, but the video leads from the monitor exceeded the common mode input voltage limits (~25 Volts?) and toasted the op-amps. May well have been a dV/dT issue. Lightning waveforms usually have a pretty ferocious rise-time. >> The operational factor here is the very high abnormal current flow >> between points of contact creating the voltage. Lightning strikes are often (theoretically) measured in kilo-amperes >even high tension cables have circuit breakers that shuts down lines >in short circuit I haven't seen circuit breakers on the source of lightning bolts. In any case, how fast can they react? Old guy
From: GangGreene on 11 Jan 2010 20:13 Moe Trin wrote: [putolin] > > Oh, like you mean the ground between the {bird|cow|person}s legs? > Yeah - had a problem like that happen. A lightning strike hit the > ground several hundred {feet|meters} away from an aircraft landing > guidance transmitter. The transmitter, transmitting antenna, and > associated electronics in one building with _three_ 25 foot/7.6 meter > long ground rods (two for lightning rods, one for the power/electroni I have seen contractors installing radio antennas/towers hire water well drillers to dig and case wells just for use as ground rod for lightning protection. The well is not meant to produce water only to serve as a huge ground rod, 8 inches in diameter and a hundred feet down.
From: david on 12 Jan 2010 23:26
On Mon, 11 Jan 2010 09:32:02 -0500, GangGreene rearranged some electrons to say: > david wrote: > >> On Fri, 08 Jan 2010 20:12:39 -0500, GangGreene rearranged some >> electrons to say: >> >> >>> Guys/Gals Please >>> >>> One question.... >>> >>> How many wires from an electrical substation to the transformer on the >>> pole? >>> >>> Answer One. >>> >>> There is no neutral. >>> The power is returned through the earth, through a ground system. >> >> Clearly you have no knowledge how an electric distribution system >> works. > > Ah yes you are correct, that is why I have been a controls engineer for > 25 years at a very large retail company. > > >> In a delta-connected system, there is no neutral. > > Not so, you could have a corner grounded delta. One could also have a 4 > wire delta system. A corner grounded delta still does not contain a neutral. > >> In a wye-connected system the neutral point is the common point where >> all three phases are tied together. > > There is a common point but I don't it's required to be connected to > ground. I will have to look it up in my NEC book. You also don't need to > use the common point wire. See section 250. > > It is a common point but really not a neutral. Remember a neutral is > only a reference point, which is useally tied to ground. > > I have seen corner grounded wye installations. Now what? That doesn't make any sense. > > >> If the three phases are balanced, there will be no net >> current and thus no voltage at the neutral point. Since the phases are >> rarely perfectly balanced, there is usually some voltage at the neutral >> point. > > Both reactively and resistance balanced of course. Power factors being > involved. > > >> A typical premises distribution transformer in the US will step down >> one single phase of a three-phase delta (or wye) transformer primary to >> 240V across two lines. The neutral is a center tap from the secondary >> winding, and is bonded to earth ground in the service entrance panel, >> per the US National Electric Code. > > It is not a neutral at the pole, just a simple center tapped xfmr with > both ends out of phase with respect to the center tap point (ie the > reference point). > > It only becomes a neutral at the service panel. No, it only becomes BONDED (a grounded neutral) at the service panel. It's still neutral. > > >> If your house (or business) has 3-phase power, it is usually a 4-wire >> (wye) system. The secondary side of the transformer is connected as a >> wye, which means the neutral is the common point of the three windings. > > Doesn't have to be 4 wire could be 3 wire wye connection. > >> Per US code, the neutral must be bonded to earth ground at the service >> entrance. > > Now what about 13.2 KV service to a building? Care to comment on that? > > Do you know what a switch gear is? 13.2kv service to a building is most likely delta. |