I've been thinking about this for a while and haven't quite figured it out, and I know y'all can help me understand...
Power goes out so some homeowner sticks his generator in his dryer plug and backfeeds the grid. Aside from all the safety no no's (we'll even say he put it in his indoor laundry room... and the CO detector battery is dead
) why doesn't the generator blow up, stop, or the breaker shut off? I'm assuming this 5000W genset is trying to power his house and the neighborhood amounting to much more than 5000W. Is it simply that the voltage drops so low (say 24V) that the power output hovers around 5000W?
Thanks!!!
Michael
I suspect that if he is actually getting to any significant load up stream he does just trip the overload on his generator. Where this might actually be dangerous is if the utility fault is right there at his transformer and he is only backfeeding his immediate neighbors. Even then I have to think the LRA of several refrigerators and the water heaters would quickly overcome all but the biggest residential generator.
This is more of the philosophical argument than a practical one.
It's also a dangerous situation. But like you, I often think about things and how equipment would react to unorthodox applications.
It's okay to think and wonder, but I would not ever consider doing this. Theoretically, it would work, provided the upstream load was very low, below output FLA of the genset. The genset breaker would protect the genset from overload, but would not survive restoration of utilty power while in operation.
Just curious? Do you know someone who is doing this, or plans to try it? I sure hope not
I don't think anyone plans to backfeed the grid, It just happens when they do something dumb.
The fact remains that generators usually kill more people than the storm, either by electrocution or CO suffocation.
Some poor linesman working up a pole is the usual victim - who else in a power outage will be handling conductors?
BTW: You don't suffocate with CO, you die of acute poisoning, if you're lucky. Survivors may take years to recover, if ever, from tiny doses.
Just curious? Do you know someone who is doing this, or plans to try it? I sure hope not
When I was stationed in Guam in 2000, there was a base wide power outage. Our generators only powered critical buildings while the rest of the base remained out. Our power on base remained off for a total of 11 hours because of emergency repair and then the outcome was someone back fed their (base housing) electrical panel with a generator. They (Ratheon) public works civilians had to check all of housing for a running generator because they backfed the grid. I do not know if the recloser at our station would not close or if they still detected power on the line after it was turned off. All I remember is being pissed off in the tropical heat on a Friday night with no air-conditioning.
Lets see, 24v into sec. of a 7200v to 120v transformer, still 1400v comming out, you hold this wire while I hook up the 24v, tell me if you feel it!Don't worry its low current just 5000 watts.
The linemen I know don't trust their own people enough to handle "dead" conductors without grounding them out first.
Standard practice on HT conductors in New Zealand is to earth the HT wires at both sides of the worksite, after the lines are proven de energised.
I take it that this standard is adapted by most POCO's around the world.
Even if someone with a 5 or 10 kVA generator tries to backfeed the grid, the existing load will absorb this amount and the generator will trip on overload or stall.
As per normal working procedures PPE is mandatory, harness, safety goggles, hardhat, full body cover overalls and insulating gloves rated at the HT voltage on the line during maintenance.
Of course care is always needed in case of backfeeding from an other source during line maintenance.
The practise of grounding HV conductors is not one of trust but one of necessity. Except on distribution radials, there are typically parallel circuits, these parallel circuits can energize a nearby isolated conductor by mutual induction and capacitance. Capacitive coupling will impart a voltage on an isolated conductor. Grounding at one point corrects this. However when you have a conductor grounded at one point, the mutual inductance with parallel current carrying conductors creates an open loop (the ground is the other half of the loop). There will be a large potential at the gap that closes this loop (the gap is between the conductor and your hand if you are in a grounded bucket). This is why a ground is installed at each end of an isolated section of line.
I haven't done or plan to do this and don't know anyone who has or plans to...
I just want to know how things work. I'm one of those that gets a toaster for Christmas and opens it to see how it works inside before I ever plug it in.
I spent a number of years as a maintenance electrician and we would try to think of all the what if's to make a system safer. Some of them were really bizarre, but one came true and because we covered that base no one was hurt. 1600 gallons per min spraying on a NEMA1 MCC 8000A 480VAC in 4+ inches of standing water and a phase to phase arc. The MCC caught fire and the GFP didn't open and only 1 fuse blew... Things like this make me think "what if".
I was thinking that when Mr. Dopey hooks his gene into the grid it would stall or breaker out, but we're still loosing linemen to backfeeds. Just wanting to learn why.
Also, hadn't thought about auto-reclosers sensing voltage downstream... After a few attempts do they stop trying to close? (Can you tell I want to learn more about HV transmission?)
Thanks everyone!!! I never stop learning from y'all!
Does anyone have a documented example of a lineman being injured from a backfed generator?
#1"When he attempted to relocate the damaged line he contacted another phase ..."
That's what killed him. I saw nothing indicating a portable generator was involved.
#2
"Although company procedures required that both ends of the primary wire be grounded, no grounds were installed ..."
There was transfer equipment installed and it was bypassed in some way I still don't totally understand. This still wasn't "energizing the grid" it was on site equipment.
The third one was "backfeeding" from the energized phase on the utility side like #1.
Anyone have one involving a residential generator backfeeding the grid? Next time I see my FPL guy I wlll ask him
Or is it Urban Legend busted?
Let's send it in to those dummies at Mythbusters...whatever they decide to prove it should be a good show.
Although they'll have to go a long way to top the 'will a water heater rocket out the roof of your house' episode.
Read the summary
Wrong kind of generator. My bad.
see note in case note 2. A generator was the possible cause.
---All I remember is being pissed off in the tropical heat on a Friday night with no air-conditioning. --AirForce ayy?
("SeaBEE", nevermind) Thanks for your service (and all others looking)!!!!!!!!!!
On #1 the summary does not seem to match the article. It almost looks like someone with an agenda wrote it without reading the "investigation" report
Power company investigators discovered that the lines had been de-energized at a pole-mounted service transformer. However, incorrect connections at this transformer established a path for current energy from another circuit to travel back (backfeed) through the transformer, energizing the line that the victim had contacted. Tests determined that 2400 volts were present on the line.
In the last one they just guessed there might be a generator involved.
The real common denominator is all of these guys violated safety rules and did not have the conductors they were handling grounded. When you are talking about the fraction of an amp it takes to kill someone that could have been coupled through any utility source, hence the rule