Generators and furnaces

[sakaran51]

Hi,
I would like to know whether the induction furnace and ladle furnace loads be connected and operated on a battery of Diesel Generators without any adverse effects.The scenario is this.

2*7MW Induction Furnaces are driven by two nos phase shifting transformers cum converter and inverter combination-24 pulse.The phase shifting transformers are connected to 13.8KV bus.There are two such IF set ups are proposed.
The DGs are of 480V 1MW capacity.The DGs will be connected to a 13.8KV bus through step up transformers.All other loads like ladle furnace and plant loads are fed thro' 13.8kv bus only. The number of DGs will depend upon the connected load.
Nature of loading and operating power factor is very much fluctuating due to the process.Moreover,is the harmonics mitigation ie.,24pulse, reasonably effective?Is the battery of Diesel Generators strong enough a source to handle such kind of loads?What precautions to be taken or system improvements to be done?

Any advice will be helpful.

 

[waross]

For 2 x 7 MW furnaces you may want to consider something larger than 1 MW generators.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sakaran51]

Hi,Bill,
There are totally 48*1MW Diesel Generators planned, out of which 32 DGs will be catering to two sets of 2*7MW Induction furnace,16MW/set.Rest of the DGs will be catering Ladle Furnace and other plant loads.The main concern is inspite of the DG installed capacity whether they can handle the fluctuation in loading,voltage,frequency ,power factor and harmonics,as the entire system is NOT connected to the Grid.

 

[ScottyUK]

I'm not any kind of expert in LV multi-generator installations but I do question if you have enough rotating mass to smooth out the wildly fluctuating load without the frequency wandering too far. In my previous employer we could certainly see the effects of furnaces at a steelworks locally connected to a fairly stiff transmission grid, and that was at a 1.8GW generating station. The furnace loads were considerably larger than yours, and there were other significant loads which we could 'see' in the behaviour of our AVR. For example, the large reversing mill was easy to spot because of the slow rhythmic cycling of the reactive power which caused the AVRs to modulate in sympathy. In your proposed installation I think your AVRs will have a tough time. A a slipring machine with a PMG AVR will likely fare better than a bus-fed AVR and brushless exciter, although you probably won't get much choice on a 1MW set.

I suggest you speak to Cummins or Caterpillar who have experience of large multi-machine generator farms and see what their applications people have to say. Or do you work for one of them...?

 

[waross]

Hi Scotty. In this size range the PMG is piggybacked on the brushless exciter.
I have used a line fed AVR to maintain service while waiting for replacement parts for the PMG.
32 sets trying to run in parallel with a fluctuating load is scary.
I would consider upping the set capacity to 5 MW to 10 MW.
Normal settings for reverse power protection may not be suitable.
I would consider islanding the furnaces.
It may be well to increase the droop settings on the governors to soften the effect of fluctuations on the diesels. This is another reason to island the furnace generators from the other plant loads.
An old style saturable transformer type AVR with current compensation may be beneficial. I have only seen a few and they were dependable and trouble free. Is anyone else familiar with these AVRs?
They may be used with a brushless exciter.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sakaran51]

Hi,Scotty,
I am not working for any DG manufacturers.I had come across a client who had been weighing different options for their proposed steel plant whether to run the plant exclusively with locally operated DG sets or combination of grid and DGs. Whatever be the combination, the possibility of the grid getting separated or grid failure can not be ruled out.Another grid source as a back up,if available,might overcome that problem.

Any var compensation and harmonic filters will help to reduce voltage and frequency excursions?And the grid voltage level?

 

[rhatcher]

I know that var compensators are typically employed for steel smelting operations. With this in mind, it may be difficult regulate this type of load without this. This would be seem to be especially true with 32 small generators. The widely varying kw and kvar requirements on a such a short time base would be very difficult to manage.

Beyond that, it seems very ineffecient and problematic to use 32 small diesel generators instead of a few large generators.

 

[rasevskii]

The OP said induction and ladle furnaces, not arc furnaces. We know that arc furnaces are a very rough load but what about induction furnaces that evidently have a frequency converter system which possibly can regulate the power level in a smooth controllable manner.

But what exactly are the ladle furnaces mentioned? More info needed here.

rasevskii

 

[ScottyUK]

rasevskii,

A ladle furnace is a type of arc furnace - in the UK they are frequently called 'ladle arc furnace'. At least one of the offenders across the fence from our generating station was a ladle arc furnace - they are a really messy load!

 

[itsmoked]

Wouldn't two combined cycle units cost less to purchase and run than 3 dozen diesels?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

I would suggest that the OP would be better connecting his generation to the local distribution / sub-transmission grid, allowing the TSO to deal with the problem loads while using the the GSU transformer impedance to provide a degree of decoupling from the awkward loads. At least. that's the way I would be thinking if I was still in the generation business.