Utility upgrade from 4.16kv to 13.8kv.

Status
Not open for further replies.
POCOs step voltage down two ways:

1. Autotranfomer

2. Isolation transformer.


When 500Kv is stepped down to 220kv or 345kv to 115kv an auto transformer is often used. 115 to 13.8kv or 34.5kv to 12.47kv is usually an isolation type (delta wye). When 12.47 has to go to 4.8kv sometimes its isolation sometimes auto.

The reasoning behind auto is that when the voltage being reduced is not a factor of more than 3x there is often a substantial savings in transformer material due to the smaller size. Thank buck boost, where a small unit can pass a huge amount of power while raising or dropping the voltage only slightly.
 
mbrooke said:
POCOs step voltage down two ways:

1. Autotranfomer

2. Isolation transformer.


When 500Kv is stepped down to 220kv or 345kv to 115kv an auto transformer is often used. 115 to 13.8kv or 34.5kv to 12.47kv is usually an isolation type (delta wye). When 12.47 has to go to 4.8kv sometimes its isolation sometimes auto.

The reasoning behind auto is that when the voltage being reduced is not a factor of more than 3x there is often a substantial savings in transformer material due to the smaller size. Thank buck boost, where a small unit can pass a huge amount of power while raising or dropping the voltage only slightly.
Click to expand...

Ok so same theory, similar applications as we do in the lv world. But grounding reference would be maintained - may not be a neutral, but still solidly grounded...
 
Usually we don't "step down " more than 2kv if we can avoid it. There is a case ground on these pots, which gets tied to a low resistance rod at the base of the pole. This is independent of the service neutral/ service ground / mgn or whatever you would like to call it. The only connection this bank has to the service neutral is the normally open 4th cutout. I'll see if I can find a connection diagram for this.

Sent from my VS986 using Tapatalk
 
interesting. I never really considered that a utility delta line might actually be grounded somewhere. Actually I partially take that back: I have entertained the possibility that a "Delta" could actually be from a wye connected secondary and just run without the neutral. I guess that is pretty much the same thing as you were discussing except there is an autotransformer in the mix.

My road is two phases of 4800 delta. Utility has two ground wires down the pole: 1 from the can (picks up secondary neutral), and a second from the arrestors.
 
Ungrounded systems( well without a service ground) are common in some of the more rural areas. At least in the region im in. If one phase has a ground fault the system will operate as normal, the second ground fault will take you out. Although that is dependant on the type of protection on the circuit. I am fairly young but in my 5 years with the poco I have never seen a recloser or sectionalizer on a delta system.

Sent from my VS986 using Tapatalk
 
Status
Not open for further replies.
Top