General question on primary / secondary selective networks 2

[Coll]

Over the weekend, I was asked if I was interested in getting involved in setting up a network that would operate as follows:

- Primary Voltage 10kV / Secondary Voltage 400V.
- 4 substations each approximately 250metres apart.
(four corners of a square).
- Network primary AND secondary selective (fully ringed on both 10kV and 400V sides).
- Each (of 4) substation has a single fan assisted transformer.
- Network can be fed from any combination of:
o Electricity Supply Company incomer
o 2 x 2MVA 10kV Diesel Generators
(so lowest possible fault level is 1x1 MVA Generator in circuit / highest is Supply Network in parallel with both generators).
- Both primary and secondary rings closed all of the time – i.e. all transformers energised and in parallel.

Now, all of my (fairly limited) experience has been on radial networks with redundant transformers operating with open couplers / auto-transfer and primary-only ring networks with an open point and no transformer in parallel.

The type of network that I have outlined above looks horrendously complex to me (and the amount of copper that has to be run to connect a functioning ring between the four substations at the 400V level is mind-boggling).

Has anybody out there set up a network like this in the past ? Am I right in thinking that the different combinations of supply and the multiple parallel paths will make for a relay setting, discrimination nightmare ?

Or is it just that this is a configuration that i am not used to and actually is quite standard and fairly easy to implement ?

Any feedback much appreciated.

Col


Clients pay to be told what you think - not what they think (but THEY don't always think that).

 

[davidbeach]

Sounds like an area network. Look for information about Network Protectors.

 

[magoo2]

Look also for "secondary networks" and also (secondary) "grid networks". Grid networks are found in many older cities in the U.S. All of these grid networks have secondary voltages of 208/120 V.

None of these operate at higher voltage like 400 V. I'd be concerned with arcing ground faults with the amount of secondary exposure involved here.

Note there are also secondary spot networks in which you parallel 2 or more transformers and primary feeders to supply a load. The secondaries are short (less than 50 meters) and they typically operate at 480/277 V or 208/120 V.

Con Edison (New York City) and Commonwealth Edison (Chicago) have extensive secondary network systems, both grid networks and spot networks.