Trafo Charging with DG Set

How else would one get anything out of the transformer secondary winding <rhetorical question - NNTR>?

Not sure what you are trying to do.

If this is for acceptance voltage level testing of the DG without the TRAFO being loaded, the answer is: Yes.

However, the inrush current will be more than 300% higher than the DG is designed for and most likely the DG protection (unless defeated) will dump/trip the DG output breaker.

It would not be a good idea to bypass/defeat the DG protection as you could suffer significant damage to the DG.

It would be best if you can close into the TRAFO load at minimum DG output voltage then ramp the voltage level up gradually allowing enough time between steps to let the load current to stabilize.

If you are testing the TRAFO, use a high quality DOBLE or other test equipment so that you can observe the reaults and record the "baseline" for future comparison.

Actually this is not a trivial question, the answer to which depends upon knowing the type of excitation system, its operating mode, and the type of generator and transformer protective scheme.

Perhaps the OP will share with us the circumstances that prompted the question.

Do you mean can you back feed the secondary 6.6kV side of a 33kV to 6.6kV transformer and get 33kV out using diesel generator(s). The answer is, it depends on the protection and transformer.

We did something similar down here for powering small islanded sections of the power grid up to 2MVA using diesel generators and a simplified mobile substation, but it required a ground-up design approach to achieve.

Yes it can be done (depending on the transformer) but you need additional equipment and protection to ensure safe operation, even if you intend to power a completely islanded (dead) section of the power grid. You will need to discuss this with an electrical consultancy.

If this is NOT what you meant please provide more information, including whether or not this is a homework or general interest question.

Jack - The electrical project manager for said mobile generator connection unit.

I think ,it is just to built up 33 kV side voltage of 20 MVA //33/6.6 kV Trafo from 6.5 MVA//6.6 kV DG set ( by keeping the DG & Trafo Breakers in close condition while switching on DG exitation slowly after DG full speed and not to take any load from DG throgh Trafo or switching on Trafo after DG builds up full voltage of 6.6 kV( which is not possible at all).To use it as black start DG set, So that main Steam TG can be synchronized at 33 kV bus with Trafo and DG could be taken off later on.

In my opinion this should be o.k ( just like or identical to building-up voltage of unit Trafo of big steamTG ).Whether it si o.k? Comments Please ?

Are you the original poster of the question as you start by making a guess as to what is going on but add quite a lot of extra detail?

First Important issue is discussion/answer to the proble or question.

Pls. post your comments

I already have based on my guess of what the original Anonymous Poster has asked.

Are you the same Anonymous Poster that posted the original question and hence are adding additional information, or like the rest of us just making educated guesses based on what little information is available?

I think you can load the 20MVA, 6.6/33KV Transformer from the 6MVA, 6.6KV DG only that the load will be limited, otherwise the DG will TRIP on OVERLOAD.

This situation will arise if the original source of supply to the 20MVA Transformer is either out on fault or undergoing maitenance. As I said earlier, the 33KV feeders will have to be REDUCED by opening some CIRCUIT BREAKERS so that the DG will not be OVERLOADED.

From explanation of 5 for the solution of problem I feel it should be possible to use 6.5MVA/6.6kV DG set as black start DG to start steam TG auxiliaries (minimum just less than DG capacity) after energizing 20MVA Trafo (initial voltage build-up) and then synchronize TG with 20 MVA Trafo at 33 kV and switch off DG. Hope it means that and my suggestion should be technically ok( However comments are most welcome to improve knowledge).

I had done it to energize 16 MVA/20kV/6.6kV. Trafo at 6.6. KV from 2 MVA DG set( Building up voltage by keeping trafo breaker (6.6 kV side in close position while starting DG).

W do it in our District Cooling Plant(5000tons of refrigeration) in Abu -Dhabi by using Gen set rated at 415volts which supply to Transformer LV to 3.3KV out put to York chillers. you have to make sure your DG has suffecient power to supply your load as it will trip the the safety protection of your load and possibility your Dg.

We uses 10 DG rated at 1500KV for 5000 tons York chiller(3.3KV) with soft starter.