My firm supplied some generators to a customer who connected them to a substation that did not have the capacity to accept the full load. Due to this, the generators are frequently tripped when generated power reaches or exceeds the capacity of the substation transformers. We've advised the customer to get connection to another substation with which they can split the capacity.

However, we are seeing another problem wherein even when the generators are not operating at rated power, the reactive power drawl is very high. Could anyone please enlighten me as to what could be the reason for this? Since the same generators are operating correctly elsewhere, I assume that the increased reactive power drawl must also be related to the incorrect grid connection but I don't know for sure. Please help!

Thanks in advance!!

 

Neo,

I have read and re-read this post several times the past couple of days--mostly hoping someone else would tackle the issues with this post.

Precisely, what is tripping the "generators"? Are you saying the generator prime movers (diesel engines? combustion (gas) turbines?) are overloaded, causing the frequency to drop and the under-frequency relays are tripping the units off-line? If that's not the cause of the tripping, please be specific.

From what you seem to be saying the load (motors; air conditioners; lights; etc.) being applied to the substation the generators and their prime movers are connected to is greater than the capacity of the generator prime movers. If that's the case, then the Customer is definitely at fault for allowing too many motors and air conditioners and lights to be connected to the substation.

You implied multiple generators were connected to this substation. Are the generators connected together before the step-up transformers, or after the step-up transformers?

Do the generator excitation systems have reactive load sharing of some kind? Is reactive load sharing working and tuned correctly? If not, then the generator excitation systems could be exacerbating the problem.

 

Hi Neo,

From what you have described, it sounds like that the generators are tripping due to attempted operation outside their capability curves. Though I am no expert, as far as I know, this could be due to:-

1] Absence of other conventional prime movers like gas/steam turbines, diesel engines, etc in the grid which could be causing a high capacitive load on you generators, causing their tripping. Non-conventional prime-movers like wind turbines usually do not have the ability to supply capacitive loading, though I don't know why.

2] Absence of capacitance banks in you grid which could be used to share the capacitive load of your generators.

Also, if your grid load is less than your supply, try to operate with maximum generators at base load, few in part load & the remaining off as this will increase your prime mover/generator life/efficiency. Also, convince your grid personnel to install some capacitance banks to supply reactive power in the grid.

Do keep us updated & try to involve some electrical experts as well.