Adaptive Setting LV Circuit Breakers for IBR Microgrids

[JezNZ]

Hi All,

Been a while since I've posted here!

Currently working on the design-build of a microgrid being the first to meet regenerative certification criteria (105% generation of consumption) in the locale I am.

The microgrid will operate both grid-connected and island-mode and is IBR HEAVY (Solar + BESS). So naturally I have the problem of protection (in)sensitivity to low fault currents in island mode.

It looks like I will be headed down the path of zone-based differential protection for MV components, however for LV it is a lot trickier to find a cost justifiable solution.

Sadly the IEEE draft guide on Microgrid Protection doesn't help much other than to suggest running studies (of course??), but there are some good papers floating around. One the most promising options suggests using "adaptive setting circuit breakers" - now I assume in principle this means you have a group of settings for grid-mode and another group for island-mode - easy!

BUT - does such a product actually exist? Commercially? In my mind I am thinking of cost efficient protection like MCCBs or Power Circuit Breakers whose microprocessor trip units can be toggled between two settings groups?

Or is this just implying I need to put in high end relaying and CTs etc and have custom logic etc? Or go old school and CTs and overload relays with shunt trips and selectable relays in different modes - neither of which are paths I would like to go down.

Will take other thoughts on creative solutions people out there have come up with!

 

[proprot]

Hove you considered something like Solkor protection ?

 

[wcaseyharman]

How much selectivity do you need in island mode?
You could use standard overcurrent elements in grid tied scenarios where there is sufficient fault current, then use time coordinated under voltage relaying during islanded situations.
Alternatively, I recently used microprocessor relays to implement voltage controlled overcurrent relays on a recent MV microgrid - I needed selectivity since the generator was installed in the middle of a distribution circuit with feeds in both directions. It worked - had a fault last week and the relaying isolated the fault and kept the rest of the system in service. You could potentially implement a similar scheme with less expensive relaying and LV breaker shunt trips.
Just some ideas, perhaps gets your mind going for other practical solutions.

 

[JezNZ]

How much selectivity do you need in island mode?
You could use standard overcurrent elements in grid tied scenarios where there is sufficient fault current, then use time coordinated under voltage relaying during islanded situations.
Alternatively, I recently used microprocessor relays to implement voltage controlled overcurrent relays on a recent MV microgrid - I needed selectivity since the generator was installed in the middle of a distribution circuit with feeds in both directions. It worked - had a fault last week and the relaying isolated the fault and kept the rest of the system in service. You could potentially implement a similar scheme with less expensive relaying and LV breaker shunt trips.
Just some ideas, perhaps gets your mind going for other practical solutions.

Hi,

Yes, a reduction in selectivity is an option being floated - I'm currently in the midst of writing a memo regarding the challenges, solutions - with next steps being high-level cost analysis, so yes alternative solution are welcome.

The network I'm looking at will be both MV & LV, distributed across a 600-800 subdivision with a BESS as community level and all houses having ~8kWp solar.

One option I've come across recently is looking at using the Eaton Power Defence MCCBs at the transformer LV distribution frames - these have a remote-triggerable maintenance-mode, ostensibly for provided arc-flash but considering using this to lower the instantaneous settings during island mode and sacrificing selectivity downstream.