Fault in a home transferred to the grid

[jim dungar]

If the first house experienced a sufficiently large fault, L-L or L-G, it is theoretically possible that the output voltage of a shared transformer could be pulled down to a voltage low enough to cause a generator to start. Failures in the backup systems are not uncommon and are often only found during actual utility failures rather than simple generator start tests.

 

[Andpie]

Yes, absolutely, This was a Generac and a common failure with them is the oil pressure switch. I have seen that before. Often, the scheduled exercise mode is not enough to cause the failure, but once it gets cranking for a while then it fails. Yes I agree. So that's a good theory, and something else happened breakers failed and power supply may have failed - too bad it puts me back to square one. Maybe I'll find out more tomorrow. Thank you. I will re-post

 

[jim dungar]

Yes, absolutely, This was a Generac and a common failure with them is the oil pressure switch. I have seen that before. Often, the scheduled exercise mode is not enough to cause the failure, but once it gets cranking for a while then it fails. Yes I agree. So that's a good theory, and something else happened breakers failed and power supply may have failed - too bad it puts me back to square one. Maybe I'll find out more tomorrow. Thank you. I will re-post

If the transfer to generator occurred, could the problems have been caused by the backup power and its failure?

The original fire may have caused an arcing type fault which, again theoretically, could have caused voltage fluctuations experienced by the other house because the transformer has a shared secondary.

Good luck.

 

[Andpie]

I don't understand how a voltage output, back fed onto the service from the "fire house" can be higher than what it's being fed from the transformer. I feel like its a fire hose pushing against a garden hose. Fault current on the other hand could be quite high, but then I have an issue understanding why there is no evidence like a tripped breaker or arcing somewhere. Hope to find out more soon. Thanks again its great to bounce this around.

 

[jim dungar]

I don't understand how a voltage output, back fed onto the service from the "fire house" can be higher than what it's being fed from the transformer. I feel like its a fire hose pushing against a garden hose. Fault current on the other hand could be quite high, but then I have an issue understanding why there is no evidence like a tripped breaker or arcing somewhere. Hope to find out more soon. Thanks again its great to bounce this around.

Both houses, on a shared transformer, create a parallel circuit. This means they will see a different amount of current but the same L-L voltage at their common point. Each house will also have some voltage drop due to its own service conductors impedance.

A low impedance fault at one house may cause its voltage to drop to zero, which could cause the shared transformer output voltage to also drop to zero. Likewise an arcing fault could cause an increase in voltage, as it sputters, raising its voltage and thus that of the other house.

The secondary side voltage issues are not often seen by the primary side because of the size of the utility and the impedance of the transformer.

 

[Ravenvalor]

We call this the "ripple effect". When you cause disturbances within your home, the rest of the power grid will feel it. Usually this shows up as unstable voltage, or a disturbance in harmonics (harmonic distortion). Imagine a pond of water that is perfectly calm. You throw a rock about the size of a tennis ball in the center of the pond, creating waves. This represents fundamental current, fundamental waveform. Now throw another rock 1/3 the size in the pond off to the right of center, creating another set of waves. Now you have created harmonic distortion, away from the original fundamental waveform. If you could measure the difference between the first waveform, and the second, you would be calculating THD, or "total harmonic distortion".

I know this is off topic but it does remind me of something that I heard on the news a few weeks ago.

Electric power grid signatures may aid in image and video verification

The new forensic technique could help determine where and when digital still images were captured.

isr.umd.edu

 

[Andpie]

OK, well for those following this thread I was able to pull up the history from the Generac whole house generator from the house across from the fire house. It showed that the gen set was running due to utility power lost within an hour of the recorded time of the fire. What I my not have explained is that the two services are routed from a common pole. The pole is on the outskirts of the fire house customer's property. Two sets of three conductors are routed down opposite sides of the pole and create individual service laterals -one to each house. When PO CO is summoned to the scene by the FD the one house is on fire and they are tasked with cutting the service to the fire house. No time to figure out which set at the top of the pole goes to which house, they cut all six causing the generator across the street to kick on. Electronic failures inside the generator house can be attributed to the disconnect / re connection of power under load by PO CO.
Fire origin was found to be started by the careless discard of smoking materials. That's what I call full circle.
Thank you everyone for your professional advise.

 

[ptonsparky]

Hopefully they pulled the transformer fuse first, vs cutting conductors willy nilly.