Furnace Transformers

[Aquarius]

Could someone help me with the following:

We have two 6 MVA 11kV/78.01V AC/AC Dd0 furnace transformers, feeding two sets of the furnace electrodes.
Our operations want to move the transformer away from the furnac for safety reason (fire etc).

The furnace electrodes are in delta configurations and are supplied from the TX LV side by busbars.
There are 8 basbars per phase and the longest set would be 7 to 8m

The relocation would require the basbars from transformers to the electrodes to be extended aproximately as follow:
Vertical +/- 3m with 2 to 3 bends
Horizontal min 5m with 4 to 5 bends

Qs:
1 is it feaasible ? ( I know furnace TX must be close to the electrodes)

2 would it change the TX parameters like R+jX or any other parameters and consequently affect the power supply to the furnace if yes what and how it would be affected ?

3 if a furnace TX can be so far away from the electrodes can we relocate the existing TX or do we have to design/buy a new one to accomodate the new parameters due to the new distance of the TX from the furnace ?

4 does anyone have a title of a good Furnace TX design book ?

I would much appreciate your help which I need urgently

 

[waross]

I have a little experience with glass furnaces.
You have left out one of the more important parameters.
What are the charicteristics of the bus bars?
You should supply at least one of the following parameters:
Physical size of the bus bars.
Voltage drop on the bus bars.
Impedance of the bus bars.
The voltage drop may be the easiest to work with.
I would suggest that if there are problems, the most serious may be voltage drop on the bus bars. I would add parallel bus bars rather than change transformers.
You may be able to compensate for longer bus bars by going up a tap on the transformer if so equiped.
Do you have any problems with circulating currents in the delta? We had an issue with a transformer overheating as a result of unbalanced primary voltages. We were using four electrodes per phase, so we were able to change to a broken delta connection with two electrodes on each winding. The transformer temperature dropped back to normal.
respectfully

 

[cuky2000]

Probably a larger bus size may be required since the additional length on the secondary bus/cabling system will increase the bus impedance and consequently additional voltage drop, losses and operating efficiency of the furnace is expected to be an issue, particularly at 78.01V AC.
_{SUGGESTION: Check all feasible alternatives such as be building firewalls with fire suppression system and run cost estimate including the production downtime cost.}

 

[Aquarius]

Thank you guys for the replays;

warros:

The basbars are 10"x7/16" HCC, 8 per phase
Do not have the impedance or VD of the busbars.

We have not recorded any problem with circulating currents .
I agree the voltage drop would be an issue and that will create problem with the furnace efficiency=>temperature etc.

In my previus post I only mentioned the vertical & horisontal bends and I forgot to mention that the total horizontal distance of relocation for one TX could be 20-30 m ! The other one would 'only' need 10m.

cuky

Thanks for your comment; I've done some research since my last post and you are spot on, voltage drop, furnace efficiency and temperature would be a big problem specially with the distance I have mentioned above.

Thank you

 

[Skogsgurra]

There is a very valid reason why furnace transformers are put very close to the furnace. Increasing the area of the busbars will not help very much because the inductivity (microhenries/metre) that has the greatest influence when you increase area. And that doesn't decrease much.

Recommend firewall etc as waross and cuky says.

Gunnar Englund

http://www.gke.org

 

[alehman]

If you could find v/m drop of the existing bus, perhaps that could be extrapolated as an approximation of what you would have for the new length. Keeping in mind that the physical arrangement is a significant factor for impedance.

The full load bus current density works out to about 2255 amps / sq. inch, which is fairly high. Is it forced air cooled?

At first glance, this seems rather impractical and very expensive. I agree with Cucky.

 

[alehman]

Make that 1300 amps/sq in. I guess that's not so high. Doesn't change my opinion though.

 

[Aquarius]

The busbars are air cooled but not forced ac, just a natural air circulation. The phase current is 16818 A at 78.01 V, there are 13 taps (78.01 V to 164.18 V)

Yes, the idea is very expensive and impractical if not unfeasible/imposible at all !

Once more I appreciate your comments, as usual this forum is fantastic;
Regards