Power Generation
- Thread starter jimmie
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physis
Senior Member
Re: Power Generation
I don't know a whole bunch about this. And if I say anything incorrect Charlie E. 'll let me have it.
I'm gonna make some guesses just for fun.
Delta would be the prefered transmission method. You don't need the extra neutral wire for transmission and you can get "Y" whenever you need with a transformer.
There is a transmission method that uses the earth as the neutral conductor. I forget the acronymn. It's only used in rural areas cause it's kind of stupid (just my opinion).
I think.
I don't know a whole bunch about this. And if I say anything incorrect Charlie E. 'll let me have it.
I'm gonna make some guesses just for fun.
Delta would be the prefered transmission method. You don't need the extra neutral wire for transmission and you can get "Y" whenever you need with a transformer.
There is a transmission method that uses the earth as the neutral conductor. I forget the acronymn. It's only used in rural areas cause it's kind of stupid (just my opinion).
I think.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Re: Power Generation
I agree!
bphgravity
Senior Member
- Location
- Florida
Re: Power Generation
Actually, the SWER system is an essential part of reducing poverty in developing nations. Communities without water pumping and purification, refrigeration, or even lighting can benefit greatly from SWER installations. I believe areas like rural Australia and parts of Africa have hundreds of thousands of miles of SWER systems in place which is providing essential power to agricultural and fishing communities.
I have been researching the systems for quite awhile now and find them very intertesting.
Actually, the SWER system is an essential part of reducing poverty in developing nations. Communities without water pumping and purification, refrigeration, or even lighting can benefit greatly from SWER installations. I believe areas like rural Australia and parts of Africa have hundreds of thousands of miles of SWER systems in place which is providing essential power to agricultural and fishing communities.
I have been researching the systems for quite awhile now and find them very intertesting.
rcwilson
Senior Member
- Location
- Redmond, WA
Re: Power Generation
Large generators are usually conencted 3-phase, 3-wire with a high impedance grounded neutral point.
The generators feed 3-phase, 3-wire switchgear conneced to delta-wye tansformers that step up the voltage to transmission line levels. The transformer's delta winding is on the generator voltage side (13.8 kv, 15 kV, 18 kv, or 27 kV), the wye winding is on the transmission voltage side (115 kV, 230 kv, 345 kV, 500 kV, etc.). The step up transformer?s HV neutral is usually solidly grounded to earth. The earth is used as a return current for any unbalanced phase currents in the system. The HV transmission lines are almost always 3-phase 3-wire with no neutral.
Some transmission lines have a fourth grounded conductor run with the phase wires but it is primarily for lightning protection and not for neutral return currents.
In the substations, most step down transformers have wye secondaries with the transformer neutral solidly grounded. Some utilities run a neutral with their distribution circuits that leave the substation, some don't. I am guessing that most do not.
So the answer to your question ?Are utility system's delta or wye?? is yes.
Sometimes delta, sometimes wye, but seldom is it a three-phase, 4-wire wye with an actual neutral, other than the ground return path.
Bob W.
[ July 05, 2005, 07:57 PM: Message edited by: rcwilson ]
Large generators are usually conencted 3-phase, 3-wire with a high impedance grounded neutral point.
The generators feed 3-phase, 3-wire switchgear conneced to delta-wye tansformers that step up the voltage to transmission line levels. The transformer's delta winding is on the generator voltage side (13.8 kv, 15 kV, 18 kv, or 27 kV), the wye winding is on the transmission voltage side (115 kV, 230 kv, 345 kV, 500 kV, etc.). The step up transformer?s HV neutral is usually solidly grounded to earth. The earth is used as a return current for any unbalanced phase currents in the system. The HV transmission lines are almost always 3-phase 3-wire with no neutral.
Some transmission lines have a fourth grounded conductor run with the phase wires but it is primarily for lightning protection and not for neutral return currents.
In the substations, most step down transformers have wye secondaries with the transformer neutral solidly grounded. Some utilities run a neutral with their distribution circuits that leave the substation, some don't. I am guessing that most do not.
So the answer to your question ?Are utility system's delta or wye?? is yes.
Sometimes delta, sometimes wye, but seldom is it a three-phase, 4-wire wye with an actual neutral, other than the ground return path.
Bob W.
[ July 05, 2005, 07:57 PM: Message edited by: rcwilson ]
charlie
Senior Member
- Location
- Indianapolis
Re: Power Generation
Most of the distribution circuits in the U.S. use a wye system (delta/wye in the substation) so that phase to neutral connections can be used for 1? transformers. It doesn't cost as for a 1? transformer if the primary voltage is in the 8.66 kV class.
Actually Bob, if the transmission line is on towers as opposed to mono-pole construction, we will normally have two static conductors above the phase wires. The wire is normally copperweld or alumaweld.
Most of the distribution circuits in the U.S. use a wye system (delta/wye in the substation) so that phase to neutral connections can be used for 1? transformers. It doesn't cost as for a 1? transformer if the primary voltage is in the 8.66 kV class.
Re: Power Generation
Charlie, could you expand upon the static wires? In other words, what exactly is their function? I know that they are insulated from the towers but where do they terminate in the substation? If they were not there what would happen. A lineman buddy of mine once told me they measured over 35KV to ground on the static wire of a 500KV tower. Does this mean they are just picking up the inductive effect of the phase conductors and bleeding it to ground?
Charlie, could you expand upon the static wires? In other words, what exactly is their function? I know that they are insulated from the towers but where do they terminate in the substation? If they were not there what would happen. A lineman buddy of mine once told me they measured over 35KV to ground on the static wire of a 500KV tower. Does this mean they are just picking up the inductive effect of the phase conductors and bleeding it to ground?
charlie
Senior Member
- Location
- Indianapolis
Re: Power Generation
Nick, Bob has already answered part of the function, ". . . primarily for lightning protection and not for neutral return currents." Most of these static wires are not insulated from the towers but are connected to the towers to bleed off any static and lightning. These are continued across the various substations and connected to the substation grounding. In the case of wood monopoles, we use a downground to a ground rod at each pole. The static is supported on single spool insulators and the static is stood off the pole where it passes through the 138 kV phase wires to keep the BIL of the line up.
Assume a transmission line being pulled in and on insulators and hanging on the stringing sheaves for a few miles. While it is resting in the pulleys, it has to be grounded to keep from building up a huge static charge from just the breeze passing over the conductors.
Nick, Bob has already answered part of the function, ". . . primarily for lightning protection and not for neutral return currents." Most of these static wires are not insulated from the towers but are connected to the towers to bleed off any static and lightning. These are continued across the various substations and connected to the substation grounding. In the case of wood monopoles, we use a downground to a ground rod at each pole. The static is supported on single spool insulators and the static is stood off the pole where it passes through the 138 kV phase wires to keep the BIL of the line up.
Assume a transmission line being pulled in and on insulators and hanging on the stringing sheaves for a few miles. While it is resting in the pulleys, it has to be grounded to keep from building up a huge static charge from just the breeze passing over the conductors.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Power Generation
Charlie wouldn't strong solar activity also contribute to static voltage build up? I have heard it can blow up transformers.
Charlie wouldn't strong solar activity also contribute to static voltage build up? I have heard it can blow up transformers.
charlie
Senior Member
- Location
- Indianapolis
Re: Power Generation
It depends on the line construction. Yes, look at the big outage several years ago in the northeast part of the country and Canada.
It depends on the line construction. Yes, look at the big outage several years ago in the northeast part of the country and Canada.
rcwilson
Senior Member
- Location
- Redmond, WA
Re: Power Generation
Wayne - Solar flares do affect transformers but usually only in the Northeast and Eastern Canada where there are long transmission lines with grounded wye connected transformers at each end. The solar flare creates a DC potential difference in the earth between the two substations. (I may have my physics wrong, the flare may induce a DC current in the line, but the results the same.)
A DC current flows up the neutral ground wire, through the windings and the transmission lines and back to earth through the other transformer windings and neutral.
This DC current saturates the transformer iron. If the transformer is loaded, the resulting over fluxing can cause thermal damage quickly and let the smoke out of the transformer. Hydro Quebec now requires transformers to be designed to handle a few 100 extra amps of DC. They also reduce load when they know a solar flare is coming.
What's fascinates me is that there must be just the right conditions of soil and rock over the span of the transmission line, a special orientation of the earth's magnetic field at that location and just the right transmission line and transformer connections. These things usually only come together in Hydro Quebec's system with their long lines from the northern dams and the geology of that part of Canada.
The solar induced currents occur elsewhere in the world, but are not large enough to cause as much damage.
Bob W.
[ July 06, 2005, 07:51 PM: Message edited by: rcwilson ]
Wayne - Solar flares do affect transformers but usually only in the Northeast and Eastern Canada where there are long transmission lines with grounded wye connected transformers at each end. The solar flare creates a DC potential difference in the earth between the two substations. (I may have my physics wrong, the flare may induce a DC current in the line, but the results the same.)
A DC current flows up the neutral ground wire, through the windings and the transmission lines and back to earth through the other transformer windings and neutral.
This DC current saturates the transformer iron. If the transformer is loaded, the resulting over fluxing can cause thermal damage quickly and let the smoke out of the transformer. Hydro Quebec now requires transformers to be designed to handle a few 100 extra amps of DC. They also reduce load when they know a solar flare is coming.
What's fascinates me is that there must be just the right conditions of soil and rock over the span of the transmission line, a special orientation of the earth's magnetic field at that location and just the right transmission line and transformer connections. These things usually only come together in Hydro Quebec's system with their long lines from the northern dams and the geology of that part of Canada.
The solar induced currents occur elsewhere in the world, but are not large enough to cause as much damage.
Bob W.
[ July 06, 2005, 07:51 PM: Message edited by: rcwilson ]
rcwilson
Senior Member
- Location
- Redmond, WA
Re: Power Generation
Sam - As to why we use "static lines" or shield wires. They are mostly for lightning protection so they are always on the top of the poles. We want the lightning strike to hit the static wire first and not the phase conductor. It is like a continuous lightning rod above the transmission line.
I wonder why we call them static wires? My Engineering Handbook only refers to them as overhead ground wires.
Bob W.
Sam - As to why we use "static lines" or shield wires. They are mostly for lightning protection so they are always on the top of the poles. We want the lightning strike to hit the static wire first and not the phase conductor. It is like a continuous lightning rod above the transmission line.
I wonder why we call them static wires? My Engineering Handbook only refers to them as overhead ground wires.
Bob W.
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