12,470 ground fault.

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JdoubleU

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In a grond fault on a 12,470 volt 3 phase system would this cause a voltage spike on the line causing damage on some office equipment.
 
Yes to a voltage spike? I must be missing something. I would say the faulted phase would see a voltage dip while fault current was flowing. And I would say if the 12,470 V system was a wye, the unfaulted phases would see a voltage swell normally around 1.25 p.u. while the fault current was flowing. When and how does a voltage spike of up to 5 p.u. happen?
 
Striking Ground Phenomenom

Striking Ground Phenomenom

wirenut1980 said:
Yes to a voltage spike? I must be missing something. I would say the faulted phase would see a voltage dip while fault current was flowing. And I would say if the 12,470 V system was a wye, the unfaulted phases would see a voltage swell normally around 1.25 p.u. while the fault current was flowing. When and how does a voltage spike of up to 5 p.u. happen?
Click to expand...

Quite the contrary, the other gentlemen are correct. It is called the Striking Ground Phenomenon in three phase systems (don't Google Stricking Ground---they refer to lightning strikes!)
Many papers have been written on the subject, I recall one long ago by FPE. I have experienced 2 in my line of work.
One was the case of a train traction motor for a people mover system(600V) The motor brush of the DC motor had dislogged from the holder and was dangling and hitting ground as the car moved. This stricking ground effect burnt up control transformers of the ground detection system of the 5 unit substations feeding the train system, symultaneously. The smoke detectors in the substations allerted Central
Control who dispached the FD. The supply (power)transformers were resistance grounded to limit the GF current and signal an alarm. Trouble was the voltage surge on the other 2 phases punctured the insulation on the ground detection control transformer primary windings and caused them to short and burn. Very amazing incedent that was a real head scratcher to isolate and find considering there were around 50 train cars total in the system. I can attached the incident report if anyone is interested in more detail.

The other one was a delta system feeding 480V pump motors for a golf course sprinkler system.
They were burning out pump motors on a regular basis. We meggered the cables to the pump MCC at 1000V but could not find anything. After using a hipot, we found the faulted cable (immersed in water filled conduit!) that was the culprit.
The intermittent striking ground punctured the motor winding insulation and caused the motor failures.
After the cable was replaced, we ended up recommending and installing a GF detection system to warn of future problems.

I like to think of an electrical system as a big tub of water with an inlet and outlet. Normally water flows in and out on a steady state basis with small surges here and there. If the tub is tipped (ground fault) the water becomes unstable and moves around the tub (voltage spike/ surge) until the water (current) becomes stable again. Ungrounded systems seem to be more unstable than grounded or resistance grounded systems but the effect appears in both.
Unless there is sophisticated line voltage disturbance equipment (Dranetz, BMI etc) installed, there is no telling what levels the other phase voltages rise to.
I guess that's what makes this stuff so fun and exciting and very lucrative :D
TT
 
tonytonon said:
Quite the contrary, the other gentlemen are correct. It is called the Striking Ground Phenomenon in three phase systems (don't Google Stricking Ground---they refer to lightning strikes!)
Many papers have been written on the subject, I recall one long ago by FPE. I have experienced 2 in my line of work.
One was the case of a train traction motor for a people mover system(600V) The motor brush of the DC motor had dislogged from the holder and was dangling and hitting ground as the car moved. This stricking ground effect burnt up control transformers of the ground detection system of the 5 unit substations feeding the train system, symultaneously. The smoke detectors in the substations allerted Central
Control who dispached the FD. The supply (power)transformers were resistance grounded to limit the GF current and signal an alarm. Trouble was the voltage surge on the other 2 phases punctured the insulation on the ground detection control transformer primary windings and caused them to short and burn. Very amazing incedent that was a real head scratcher to isolate and find considering there were around 50 train cars total in the system. I can attached the incident report if anyone is interested in more detail.
/QUOTE]

Wirenut's doubt is justified.For a resistance grounded system,the value of resistance can be chosen suitably that over voltage does not occur in other healthy phases.Only in ungrounded systems such high over voltages are liable to occur.
Click to expand...
 
The other one was a delta system feeding 480V pump motors for a golf course sprinkler system.
They were burning out pump motors on a regular basis. We meggered the cables to the pump MCC at 1000V but could not find anything. After using a hipot, we found the faulted cable (immersed in water filled conduit!) that was the culprit.
The intermittent striking ground punctured the motor winding insulation and caused the motor failures.
After the cable was replaced, we ended up recommending and installing a GF detection system to warn of future problems.
Click to expand...

PVC conduit?

Unless there is sophisticated line voltage disturbance equipment (Dranetz, BMI etc) installed, there is no telling what levels the other phase voltages rise to.
I guess that's what makes this stuff so fun and exciting and very lucrative.
Click to expand...

BMI! Man you have been around a while, I still have 3 of their units collecting dust. I bought one of the first 4800?s
 
brian john said:
PVC conduit?

No, steel.

BMI! Man you have been around a while, I still have 3 of their units collecting dust. I bought one of the first 4800?s
Click to expand...

Yeah, just an old fart!:D
Remember the Dranetz 606? It was a V disturbance meter that printed out
text on a roll of paper! I think it was the first line disturbance meter on the market.
I hate the new Fluke version.RPM makes a decent unit. I think the best one made was the Dranetz 658,
which we have 2 and still use today.
TT
 
I worked for a firm that had a 606, The new Fluke 1750 could improve immensely just by copying some of the RPM reporting software. Fluke bought RPM, I do not see why the 1750 is not a better meter.
 
There's a 606 in my garage :D. Last time I plugged it in, it worked pretty well once it cooked for a day. The sample&hold dumps would get out of whack and register almost continuous impulse events until then. (A 4066 cmos switch, IIRC. Why do I remember things like this?)

I'm working on and off on a disturbance logger based on a PC audio card. Maybe some year I'll do the software....
 
tonytonon said:
Quite the contrary, the other gentlemen are correct. It is called the Striking Ground Phenomenon in three phase systems (don't Google Stricking Ground---they refer to lightning strikes!)
Many papers have been written on the subject, I recall one long ago by FPE. I have experienced 2 in my line of work.
One was the case of a train traction motor for a people mover system(600V) The motor brush of the DC motor had dislogged from the holder and was dangling and hitting ground as the car moved. This stricking ground effect burnt up control transformers of the ground detection system of the 5 unit substations feeding the train system, symultaneously. The smoke detectors in the substations allerted Central
Control who dispached the FD. The supply (power)transformers were resistance grounded to limit the GF current and signal an alarm. Trouble was the voltage surge on the other 2 phases punctured the insulation on the ground detection control transformer primary windings and caused them to short and burn. Very amazing incedent that was a real head scratcher to isolate and find considering there were around 50 train cars total in the system. I can attached the incident report if anyone is interested in more detail.

The other one was a delta system feeding 480V pump motors for a golf course sprinkler system.
They were burning out pump motors on a regular basis. We meggered the cables to the pump MCC at 1000V but could not find anything. After using a hipot, we found the faulted cable (immersed in water filled conduit!) that was the culprit.
The intermittent striking ground punctured the motor winding insulation and caused the motor failures.
After the cable was replaced, we ended up recommending and installing a GF detection system to warn of future problems.

I like to think of an electrical system as a big tub of water with an inlet and outlet. Normally water flows in and out on a steady state basis with small surges here and there. If the tub is tipped (ground fault) the water becomes unstable and moves around the tub (voltage spike/ surge) until the water (current) becomes stable again. Ungrounded systems seem to be more unstable than grounded or resistance grounded systems but the effect appears in both.
Unless there is sophisticated line voltage disturbance equipment (Dranetz, BMI etc) installed, there is no telling what levels the other phase voltages rise to.
I guess that's what makes this stuff so fun and exciting and very lucrative :D
TT
Click to expand...

Happy Friday! These examples are cases of a re-striking ground fault and I can see that causing damage. The original question was about a ground fault on a 12,470 V system causing damage to 120 V office equipment. I don't see how that could happen. Anybody have any literature on the subject? I would be interested to see it from those that responded yes. :)
 
wirenut1980 said:
Happy Friday! These examples are cases of a re-striking ground fault and I can see that causing damage. The original question was about a ground fault on a 12,470 V system causing damage to 120 V office equipment. I don't see how that could happen. Anybody have any literature on the subject? I would be interested to see it from those that responded yes. :)
Click to expand...

Sorry for getting off of the subject. Ground fault damage does not cross over to different system voltages (thru transformers)
based on case studies, do not have an answer for you.
:(
tony
 
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