EGC at utility xfmr

[winnie]

I'm not a utility engineer; I only know what I've read and what I've seen on the poles that I've looked at.

To be clear, I'm talking about the distribution level voltages on poles, the last 'high voltage' prior to the transformer which feeds the customer.

Most of the transformers that I've seen have a single HV bushing, and the HV coil has to be connected between that terminal and some other low voltage terminal. My understanding is that this is usually the grounded can itself. In this case the 'ground' conductor which usually runs along the poles is being used as the neutral conductor for the distribution system.

-Jon

 

[coulter]

...however it is very common to develop extreme voltages with very little charge (and very little total energy) simply from stuff moving around. ...

Okay, got that. Winter time, dry air - slide out of the car seat, touch the door - zap

... Helicopter blades moving through the air can develop a significant fraction of a milliamp of charging current, for example. ...

Okay, I've seen that. helios dangling loads, will deliver a pretty good shock if one grabs the tag line before it touches the ship deck.

... The energy in these transients may be quite small, but it can damage insulation....

Perhaps you could give a little more explanation or some references. I've never heard of helios damaging MV or HV conductor insulation. (Other than flying into them)

carl

 

[Psychojohn]

Jon,

How do they have the distribution system neutral? Typical their distribution is 3 phased conductors so they don't have a neutral to bond. I am confused.

The utility delivers 3P wye, with a neutral. Which is then seperated into 3 single phase circuits for residential use.

 

[72.5kv]

the neutral serves both the primary and secondary. in its sized to carry from between 50% to 70% of the maximum load current of the primary feeder. ex. 795 phase conductor with 4/0 neutral. those lines are fairly balanced, although it can be a juggling act. this from experience interning at a power company

as far as the single bushing can, on the side of it is a neutral lug. this lug is the would be the equivalent of the H2 bushing. the utility neutral goes there and thus complete the primary circuit.

 

[dereckbc]

Have not read through all the replies, but the reason POCO will not allow the EGC from the service transformer is simple Liability Issues. No POCO or insurance company of them will have anything to do with it.