Electricians or people that understand wiring, test me

[NightShade]

I actually saw a guy run 3 phase on 220 and then he said he was actually able to run it on 110. Basically applied the 220 and then pull started it. Once it was up to speed it would stay running on 220 without issue. Later on when he had multiple 3 phase motor's running he used the 3rd leg to start others and then when multiple 3 phase motors were running each one could be dropped to just running on 110. Don't know how long ago this was but I guess the electric company was having issues because his electric bill would sometimes show negative and rarely was as much as they expected. Anyway the story goes that because of the way he was doing things there was some sort of a ripple being introduced to the meter and it was not reading correctly. They actually pulled his meter at one point thinking he was tapped in somehow and stealing power. He said he would start the system up and then leave it running for days on end.

 

[NightShade]

By controlling generator speed. A 2 pole generator requires 3600 rpm to generate 60 hz. A 4 pole generator requires half that speed.
When your bringing a power plant generator online, the phases are matched through the control system and a synchroscope that tells the generator where the grid phase is. When they match, there are two options. The operator can manually sync the generator by throwing a switch at the right time that is critical, or allow the later model electronic control systems to do it electronically.
When I say critical, it's a breathtaking moment when syncing a 550 megawatt steam driven generator to the grid. If your 1/10 of a cycle off, some bad stuff is fixing to happen. Huge 200' long generators have screamed to a halt and actually spun backwards. Never saw that, but had industry reports with details.

Very cool, I knew they had to stay in phase or it would cause some sort of problem but always wondered how it was done so there were not ripples in the waveform. I know that the grid tie power inverters will watch the grid for a bit when everything first is connected and then match it's waveform to the grid and then feed a slightly higher voltage.

 

[dennishoddy]

Did you ever work with any of the PLC controls (or like controls) that they use to set something like this up?

I've worked with every Allen Bradley PLC from the PLC-2 to the 5 I think it was until they went to the latest system using the data highway systems in the early 2000's including CNC. Programming and repair. Several other PLC systems as well. Those old ladder diagram systems are just about obsolete now. Systems have become too complex and they are too slow to respond.
Now they operate of a data highway system similar to the cloud. Heck I've been out of it for over 5 years now since retiring. I'm betting there is some more amazing stuff out there now that wasn't thought of 5 years ago the way technology is advancing.

 

[dennishoddy]

Very cool, I knew they had to stay in phase or it would cause some sort of problem but always wondered how it was done so there were not ripples in the waveform. I know that the grid tie power inverters will watch the grid for a bit when everything first is connected and then match it's waveform to the grid and then feed a slightly higher voltage.

When an out of phase upset occurs, the generator becomes a motor and that's when the bad stuff starts happening. You lose total control of the control system, and the generator/motor can hunt for higher speed until it comes apart. The armature shaft on a 550 megawatt steam generator is 3' thick with all the turbine rotors attached in three stages. I don't remember how many tons it weighs but it's in the hundreds of tons.
A plant in England motored a generator and it came out of its housing, spun into the control room and killed everyone inside. Dozen or so folks, many years ago. Now all power plant generators are designed to spin away from the control room if they motor and come out of their housing as a safety issue.

 

[NightShade]

When an out of phase upset occurs, the generator becomes a motor and that's when the bad stuff starts happening. You lose total control of the control system, and the generator/motor can hunt for higher speed until it comes apart. The armature shaft on a 550 megawatt steam generator is 3' thick with all the turbine rotors attached in three stages. I don't remember how many tons it weighs but it's in the hundreds of tons.
A plant in England motored a generator and it came out of its housing, spun into the control room and killed everyone inside. Dozen or so folks, many years ago. Now all power plant generators are designed to spin away from the control room if they motor and come out of their housing as a safety issue.

Yikes. I don't think I would want to be in the same county as one of those things acting up. Too much weight spinning around to get loose like that. It is amazing how much mass is spinning around just to keep the lights on.

Makes me wonder something else though, do the wind turbines create ac that is fed to the grid directly or is there some sort of inverter in use. Since wind speed is variable and they are direct drive it's not likely they would spin at just the right speed all the time.

Also when one of the generators has an issue that causes them to slow down and drop out of phase can the same thing happen where it motor's?

 

[dennishoddy]

Yikes. I don't think I would want to be in the same county as one of those things acting up. Too much weight spinning around to get loose like that. It is amazing how much mass is spinning around just to keep the lights on.

Makes me wonder something else though, do the wind turbines create ac that is fed to the grid directly or is there some sort of inverter in use. Since wind speed is variable and they are direct drive it's not likely they would spin at just the right speed all the time.

Also when one of the generators has an issue that causes them to slow down and drop out of phase can the same thing happen where it motor's?

I'm not versed on the wind turbines. I know they can change the pitch of the blades to maintain some sort of steady speed, but I've seen them spinning so slow, that I wonder if they are actually working or not. I know each wind farm has a substation to interface to the grid, but what I don't know is how they sync and maintain voltage.
Just spitballing, but I'd think it would have to be an alternator and not a generator similar to what is on a vehicle. Back in the day when autos sported generators, the accessories would vary up and down in speed with the speed of the generators, while the newer alternators maintain constant voltage and amperage through their design.

 

[NightShade]

Right, I have wondered if they do some sort of trickery to make it all work. I would not be surprised if a type of inverter is used to take the power generated on the wind farms and turn it into what is needed for the grid. Kinda how a lot of the smaller systems work. Take 3 phase ac at whatever voltage, amperage, and frequency then convert to DC then take that and convert back to AC at the right voltage and frequency. I know the conversions are all creating a loss but they have to convert the DC on the solar farms to AC as well so whats an extra step.

 

[dennishoddy]

Right, I have wondered if they do some sort of trickery to make it all work. I would not be surprised if a type of inverter is used to take the power generated on the wind farms and turn it into what is needed for the grid. Kinda how a lot of the smaller systems work. Take 3 phase ac at whatever voltage, amperage, and frequency then convert to DC then take that and convert back to AC at the right voltage and frequency. I know the conversions are all creating a loss but they have to convert the DC on the solar farms to AC as well so whats an extra step.

Very possible. I just don't know to be honest.

 

[travisstorma]

Correct. There are several ways turbines get the power out, but one of the most common is to change the rotational generator AC to DC then back to AC again using some sort of inverter while syncing up the AC phase.

 

[dennishoddy]

Correct. There are several ways turbines get the power out, but one of the most common is to change the rotational generator AC to DC then back to AC again using some sort of inverter while syncing up the AC phase.

Figured there was someone on here that would know.