Open Neutral
Senior Member
- Location
- Inside the Beltway
- Occupation
- Engineer
When you were a kid, did you play the "Who spotted the VW Bug first" game....? Another EE and I do an adult version.
As we drive various places, we follow the 33 and 69KV PEPCO feeders (and some BG&E) from switchyard to subs, then compare notes trying to reverse-engineer their grid. (Our interest started on the NE Corridor 25Hz system, but I digress.) You can play at home as well, thanks to Google Earth and Bing Birds-Eye imagery...
We've found some ...interesting... designs, such as the 69 KV feeder that crosses Rt 29 underground, emerges, runs exactly one pole & then goes underground again into the sub. Why didn't they just.....?
So I have some dumb questions....
We're guessing that originally the substations were fed with 33, but upgraded to 69 later. On [1] there is a 69->33KV sub by White Oak, and right across the street, a 33->13.8 one. So we wondered if anyone used a triple voltage transformer, saving the 2nd step.
On #3, we have not found anything commercial above 13.8, even going to large shopping malls, but there's a big water treatment plant in Laurel that appears to be fed with 33KV from two directions. In Nowhere, MD there is some ilk of aluminum smelter which he says is fed at 132 KV. {"Guess they have the phone number to PJM taped on the wall" he noted.]
We have followed several feeders with 33KV insulators but one running between subs has 4-5 poles in the middle with ordinary 13KV insulators....and then we noticed neither end went anywhere. They did put it all back up following the derecho... My guess was it was still being included in the rate base but then I have a suspicious mind.
The 69KV sub feeds always seem to be below ground. But in one case, 4 blocks away it descends, and 3 blocks away it emerges again. It would make sense if they bracketed the substation but nope, both are south of it....and the overhead continues north almost past the sub..
Anyone want to enlighten us with their informed speculation?
As we drive various places, we follow the 33 and 69KV PEPCO feeders (and some BG&E) from switchyard to subs, then compare notes trying to reverse-engineer their grid. (Our interest started on the NE Corridor 25Hz system, but I digress.) You can play at home as well, thanks to Google Earth and Bing Birds-Eye imagery...
We've found some ...interesting... designs, such as the 69 KV feeder that crosses Rt 29 underground, emerges, runs exactly one pole & then goes underground again into the sub. Why didn't they just.....?
So I have some dumb questions....
- Are there any tri-voltage transformers used at subs?
- What is the typical capacity available on 33 & 69 KV feeders?
- When do utilities feed customers at anything above the usual? {13.8 here..}
- Why maintain dead feeders?
- Why are subs fed underground?
We're guessing that originally the substations were fed with 33, but upgraded to 69 later. On [1] there is a 69->33KV sub by White Oak, and right across the street, a 33->13.8 one. So we wondered if anyone used a triple voltage transformer, saving the 2nd step.
On #3, we have not found anything commercial above 13.8, even going to large shopping malls, but there's a big water treatment plant in Laurel that appears to be fed with 33KV from two directions. In Nowhere, MD there is some ilk of aluminum smelter which he says is fed at 132 KV. {"Guess they have the phone number to PJM taped on the wall" he noted.]
We have followed several feeders with 33KV insulators but one running between subs has 4-5 poles in the middle with ordinary 13KV insulators....and then we noticed neither end went anywhere. They did put it all back up following the derecho... My guess was it was still being included in the rate base but then I have a suspicious mind.
The 69KV sub feeds always seem to be below ground. But in one case, 4 blocks away it descends, and 3 blocks away it emerges again. It would make sense if they bracketed the substation but nope, both are south of it....and the overhead continues north almost past the sub..
Anyone want to enlighten us with their informed speculation?