Sizing of Drop Out Fuse

you are trying to tie the existing 11 kv circuit to the the 20 kw plant thru the 100 kva transformer. The max output of the 20 kw at 11 kv = 1.05 amps and 29 amps a 0.4 kv. The max load at 11 kv on the 100 kva transformer = 5.25 amps. You need to more concerned with protecting the hydro plant as it can only deliver 1 amps to the 11 kv system. Not sure what you are trying to accomplish but 1 amp is not much of an improvement.

Thank you for your answer. But I want to utilize the existing transformer to inject excess power to the grid when the isolated load is less than 20kW.

This seems like an odd match, with the transformer four times as large as necessary.

What provisions ensure that the hydro will be in synch when putting it onto the grid?

Guest quote "Thank you for your answer. But I want to utilize the existing transformer to inject excess power to the grid when the isolated load is less than 20kW."

You want to inject excess power to the grid but the max is only 20 kw. That is a very small amount of power. What kind of load are you trying to help by doing this?

From this transformer other villages are electrified. But I donot know exactly the villages load. I want to connect 20kW to this transformer. This 20kW Plant also supply power to the villages but during night, there is no load and the whole 20kW can be injected into the grid via this transformer. So I want to know about the sizing of drop out fuse.

Think about it like this. The max load that you can supply thru the 100 kva transformer is 20 kw. As previously posted that amounts to 20kw/(0.4x1.73) = 29 amps fed from the hydro plant. So to protect the plant you need to install a 30 amp breaker on the 400 volt side of the transformer. This will allow you a max of 20.7 kw thru to the 11 kv grid. Is this the only source to the grid? You need to try to keep the load balanced as close as possible. Does this answer you question? Where are you located?

Thank you. Then it will be 1.5 Amp breaker for 11kV side right?? Should not I consider power factor 0.8 (however it is a synchronous generator) to calculate capacity of breaker? Or it implies only for asynchronous generator? It is from one of the village of Nepal.

1.5 amp should work. I would not worry about the PF. What kind of load do you have? Is it just lights and small appliances? How many houses are connected?

143 Households with around 100 watt per house, 5 computers only at day time and 1 saw machine only at day time and its capacity is 2.2kW. Load is inductive.

You should be ok. If the length of the 400 volt cable from the power plant is long you need a breaker at the plant to protect in case of a cable fault. That is why I suggested a 30 amp breaker in post 6. What is your background in this type of work? Do you have many of these projects? Just curious? Send your email to me via this forum and I will respond.

Oh! I am the Master of Science in Power Engineering Student in Germany originally from Nepal (Kathmandu). This is my Master Thesis about the Grid connection of 20kW MHP without Interrupting isolated load. Thank you very much for your quick response.

As the purpose of the <...Drop out fuse...MCCB...> circuit protection device is to protect the cabling installation, information on which has been withheld, the question is unanswerable.