Undergrounded distribution

[Mbrooke]

Evaluating the under-grounding of miles of distribution circuits in some new/old builds. Is a higher voltage like 34.5kv better or a lower voltage like 2.4-13.8kv better? My understanding is that reactive currents are greater as voltage increases. Also the odds of resonance and ferroresonance go up.

 

[cuky2000]

To achieve an optimal distribution design, harmonization of several conflicting factors needs to be evaluated such as system cost, losses, voltage regulation, reliability, maintainability, etc.

Yes, UG systems with sub-transmission voltage such as 34.5 kV are more prone to develop ferroresonance than 15 kV class voltage level due to the interaction between the large cable capacitance and reactance of light loaded transformers.
Examples of this phenomenon have been documented in the power distribution industry. Here is a reference article indicating the type of ferroresonance problems commonly encountered on distribution systems at 34.5 kV.

 

[Mbrooke]

Thank you- this is what I was looking for.

Few questions:

1) is ferroresonance a medium or high risk phenomenon when all the 15kv circuits are underground? To the point 15kv vs 34.5kv no longer matters?

2) What are the reactive power requirements across a 15kv system vs a 34.5kv system?

3) Would you design a system with single core cables or multi core cables?


To clarify I don't have an industrial or institutional power system in mind but entire towns and cities where 120-250MWs of overhead capacity is buried underground. Suburban setting, not rural.