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amits
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Charging 750MVA 300/400KV Transformer

06/08/2011 1:16 AM

We are operating a grid of around 11,000MW. Recently we have commissioned a 400KV substation which will evacuate 2000MW from a generating Station. This 400KV substation has 4 transformers of 750MVA each. In case of total collapse of the grid, can we back charge these transformers with 6*42 MW gas turbine having black start capability or we have to build up the grid and then charge the transformer after having sufficient number of units available to handle the inrush current of the transformer. The transformer is around 120 Km away from the Gas Turbine Power Plant. Is there any thumb rule for calculating the amount of equivalent generation available on the grid for charging such a large capacity transformer.
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Tornado
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#1

Re: Charging 750MVA 300/400KV transformer

06/08/2011 1:18 AM

Duplicate thread alert!

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nikolay
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#2

Re: Charging 750MVA 300/400KV Transformer

06/09/2011 1:33 AM

There is no rule of thumb for this .

Just do the math as it is usually done. For your generators the charging of a transformer represents a disturbance. This means that you have to check the dynamic stability for your gas turbines and generators. Good luck in finding a good engineer to get you out of the trouble.

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raghunath7
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#3

Re: Charging 750MVA 300/400KV Transformer

06/11/2011 6:42 PM

The charging current needs to be limited. [Inrush current]

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amits
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#4
In reply to #3

Re: Charging 750MVA 300/400KV Transformer

06/12/2011 1:02 AM

Thanks. You are right. But how it can be limited. I have suggested that we may charge the transmission line ( 120KM long) along with the primary of the transformer to limit the inrush current. But some one else is suggesting that the transmission line ( which is also 120Km long) will make enough difference and I differ with that opinion. Unless we have enough number of generating units, we should not charge the transformer as stand alone. Is there any thumb-rule that may help in this regard.
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raghunath7
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#5
In reply to #4

Re: Charging 750MVA 300/400KV Transformer

06/12/2011 1:13 AM

Since the orignial question says "In case of total collapse of the grid, ", I would suggest that this can be charged along with generating units, where the , generator excitation is slowly increased to rated value.

i.e. Transformer will be in the circuit being charged. The generator excitation is kept low and slowly increased to rated value.

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amits
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#6
In reply to #5

Re: Charging 750MVA 300/400KV Transformer

06/12/2011 1:20 AM

Dear Sir,

Thanks. That was possible when this was the generator transformer but this transformer is a bit away and voltage levels are 11.5/132/275/400KV. Also that is not possible as generators are under different Company and we manage the operation on grid. What is your opinion on charging with transmission line on primary side.
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raghunath7
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#7
In reply to #6

Re: Charging 750MVA 300/400KV Transformer

06/12/2011 1:32 AM

The transmission line impedances are generally lower than the transformer series impedance [or % impedance].

I doubt whether charging through transmission line will limit the inrush currents.

Since you have already mentioned the possibility of charging the transformer usine 6*42 MW gas turbines, the whole network may be started as in generating station, with "0" voltage , and gradually increasing the generator voltage.

You can perform EMTP studies of the corresponding network conditions and assess the impact of charging by various means.

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amits
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#8
In reply to #7

Re: Charging 750MVA 300/400KV Transformer

06/12/2011 2:00 AM

Thanks a lot. Including transmission line was like something is better than nothing.
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