reasons behind this transformer current
reasons behind this transformer current
(OP)
i have an outdoor Transformer of 500KVA, 13.9 /.6 KV, The low voltage side Y is grounded by the transformer,and a feeder cable is connected to the main panel inside the building.
when i shut down the main panel, i found that there is a 0.9 amp flowing from the nuetral cable to the ground inside the building (which is the connected to the main water pipe).
can any body tell me the possible reasons behind this current and how to rectify it please
Regards
when i shut down the main panel, i found that there is a 0.9 amp flowing from the nuetral cable to the ground inside the building (which is the connected to the main water pipe).
can any body tell me the possible reasons behind this current and how to rectify it please
Regards






RE: reasons behind this transformer current
The above case does not apply to networks employing PME.
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If we learn from our mistakes I'm getting a great education!
RE: reasons behind this transformer current
Or
Although there is no load on the transformer there will still be capacitive charging currents. An unloaded transformer may have a non-sinusoidal voltage waveform which will develop harmonic components which will return from ground on the neutral. 0.9 is only about 0.19% of full load current.
Bill
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"Why not the best?"
Jimmy Carter
RE: reasons behind this transformer current
however, the transformer is away from the building, and the main building panel is grounded via the armored of the tech cable feeding the panel from the transformer,
do you mean that we have to connect the water pipe (or the grounding rods) of the building to the main transformer ground,
thanks in advance for your reply.
RE: reasons behind this transformer current
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: reasons behind this transformer current
RE: reasons behind this transformer current
To avoid parallel paths and consequent current division, normally you would not want an equipment ground between the transformer and service equipment. The NEC specifically allows a continuous cable sheath to be bonded to the grounded conductor at only one point. If the sheath is connected at both ends and assuming the service equipment is properly grounded, and it is permitted by your codes, you might consider disconnecting the sheath ground at the service equipment.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: reasons behind this transformer current
- Yes it is in Canada.
- Normally the outdoor transformer has its own ground, and the building has its own ground as well, by code how can we eliminate this current by connecting the building ground with the transformer ground?
any other ideas please
Thanks again
RE: reasons behind this transformer current
RE: reasons behind this transformer current
Why are you bothered about this? Stray currents flow around all the time in ground loops if anything is energized around anywhere. I suppose that you are using a digital clamp-on meter to read this. Overkill, too much sophistication in your measurements. Harmonics, as said. If it was tens of amps then it would be worth looking at.
In energized substations, it is usual to find stray amps flowing around: in railings, water pipes, fences, ironwork, grounding wires to metal boxes...Take your clamp-on and do a few readings around the place in the ironwork, always an interesting but useless exercise.
regards, rasevskii
RE: reasons behind this transformer current
Thank you for your response,
According to CEC yes two grounds are connected to neutral, one at the outdoor transformer side (four 10feet rods bonded together), and the other ground is inside the building connected to the main panel, (ground rod bonded to the water pipe0.
My concern is can I connect the Tr and building grounds together in order to eliminate this 0.9 amp, and is there a code that I can lean on?
Thanks
RE: reasons behind this transformer current
Regards,
PowerfullStuff
RE: reasons behind this transformer current
RE: reasons behind this transformer current
600/(root 3) * .9A is not a lot of power and could be real load.
GL
RE: reasons behind this transformer current
0.9A isn't much. There are a very few scenarios where this might not be tolerated. Services to diaries come to mind as one. Cows don't much like being part of the neutral return path through grounded milking machines. The solution here is to disconnect the secondary neutral bonding to the transformer case and primary neutral and depend only on the service entrance ground (your water pipe may need to be enhanced by a well engineered multi electrode premises ground system). Utilities don't like to do this (if they own the transformer). Ours insisted on warning labels at the transformer in the event the service neutral was to be disconnected. If something (like a cow) isn't being bothered by 0.9A, leave well enough alone.