Supply to feeder pillar - no incomer?

Jam: 
 

First thought: Not my preferred arrangement, and I've seen this kind of thing end badly.

Sounds like a solar park to me, or similar… What does the G99 relay operate - a main contactor somewhere or each of the generators? Where (and what) are the main and emergency points of isolation (maybe at HV)?

The HV designer should be able to provide comfort that the transfomer feeder protection provides cover for LV faults within sufficient time at least as far as the MCCBs (including earth faults)… Being close-coupled in principle the answer should be similar to having an upfront ACB, but the risk of internal faults is somewhat increased (particularly given the application). Note that even if it does it is likely to be significantly slower than an LV protective device so resulting damage will be considerably greater.

Conversely the MCCBs (and any auxiliary circuit OCPDs) would need to be rated for the full prospective fault of the transformer, since there's no backup/current limiting. so they might be bigger than you'd otherwise need.

Is overload protection needed?

Is it satisfactory that HV operations are required to maintain and inspect the LV switchboard The construction / separation / form of the switchboard will also inform the discussion.

Hi Jam and thank you for your reply. You are spot on - this is a new sub that will be connected to RMU with other nearby subs on HV side and will have a connection to two panelboards, one getting power from PV and second providing power for new EV points.

In terms of what G99 operates - it is connected with outgoing MCCBs and picks up under/overvoltage and overloads detected anywhere in LV side. From limited plans I have (unfortunately this is not my project and I am not directly involved with this) it doesn't actually show how it kills the power that comes from TX into the feeder pillar so I was hoping for a bit of clarification from whoever encountered this solution before.

Feeder pillar is Form 4. Is it satisfactory to do HV operations to maintain and inspect LV switchboard? In my mind no, but unfortunately I am not a designer at this job and I am questioning what has been proposed and is being built.

Jam: 
 

First thought: Not my preferred arrangement, and I've seen this kind of thing end badly.

Sounds like a solar park to me, or similar… What does the G99 relay operate - a main contactor somewhere or each of the generators? Where (and what) are the main and emergency points of isolation (maybe at HV)?

The HV designer should be able to provide comfort that the transfomer feeder protection provides cover for LV faults within sufficient time at least as far as the MCCBs (including earth faults)… Being close-coupled in principle the answer should be similar to having an upfront ACB, but the risk of internal faults is somewhat increased (particularly given the application). Note that even if it does it is likely to be significantly slower than an LV protective device so resulting damage will be considerably greater.

Conversely the MCCBs (and any auxiliary circuit OCPDs) would need to be rated for the full prospective fault of the transformer, since there's no backup/current limiting. so they might be bigger than you'd otherwise need.

Is overload protection needed?

Is it satisfactory that HV operations are required to maintain and inspect the LV switchboard The construction / separation / form of the switchboard will also inform the discussion.

Hi Jam and thank you for your reply. You are spot on - this is a new sub that will be connected to RMU with other nearby subs on HV side and will have a connection to two panelboards, one getting power from PV and second providing power for new EV points.

In terms of what G99 operates - it is connected with outgoing MCCBs and picks up under/overvoltage and overloads detected anywhere in LV side. From limited plans I have (unfortunately this is not my project and I am not directly involved with this) it doesn't actually show how it kills the power that comes from TX into the feeder pillar so I was hoping for a bit of clarification from whoever encountered this solution before.

Feeder pillar is Form 4. Is it satisfactory to do HV operations to maintain and inspect LV switchboard? In my mind no, but unfortunately I am not a designer at this job and I am questioning what has been proposed and is being built.