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k.dhana
Associate

Join Date: Aug 2008
Location: TN, India.
Posts: 35
Good Answers: 2

Generator Bus Duct

07/11/2010 11:20 AM

.........

In generator winding the conductors has much needed forced cooling by Water and/or Hydrogen. The current flow in Generator bus bar in bus duct is also same as in Generator winding but the not that much of cooling is required. In case of 500 MW / 0.8 pf generator the full load current is in the range of 16 Kilo Amp, even though the bus duct doesn't has any forced cooling.

( it is arguable that, inside the casing the other losses causes much heat and winding heat is to be extracted by external medium)

In bus duct the surrounding is heat free but a sealed one hence there will not be no any heat removal. Needs clarification.

Thanks always.

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mountk2
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Join Date: Jun 2010
Posts: 348
Good Answers: 10
#1

Re: Generator Bus Duct

07/11/2010 1:53 PM

Why do you assume that crossectional area of alternator winding and bus duct conductors is same and why don't you take into consideration that winding is embeded in slots with wires bundled together in insulation with minimum air circulation as against the case in bus duct.

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msamad
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Join Date: Feb 2009
Location: Houston, USA
Posts: 946
Good Answers: 244
#2
In reply to #1

Re: Generator Bus Duct

07/11/2010 6:31 PM

Mountk2's question already answers your question. Here it is with more explanation.

The primary reasons are:

(1) The heat loss in generator is much more than the heat loss in bus duct. This heat loss in generator is due to core loss and copper loss in both stator and rotor including the windage and frictional loss.

(2) The total length of current carrying part is much more within the generator than within the bus duct in comparison to the heat dissipation area.

(3) Due to space limitation, generator winding bar cross sectional area is less than the busbar cross sectional area used in the bus duct for the same amount of current. The bus bar size of the bus duct is designed so that the heat loss within the bus duct keeps the inside temperature within tolerable the range.

Hope it is understood.

- MS

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pcchatur
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Join Date: Mar 2010
Location: BHOPAL, INDIA
Posts: 201
Good Answers: 20
#3

Re: Generator Bus Duct

07/11/2010 11:32 PM

The stator winding cross-section has a limitation of stator slot dimension. Further, it is insulated by insulation tape for the rated voltage of the generator. This insulation is bad conductor of heat and therefore heat transfer through is poor (unless you use direct cooled winding. Most of the windings in the range of 500MW rating are direct water cooled or direct gas cooled). For bus duct conductor there is no limitation of its size and it has lot of surface area for heat transfer. It is supported in insulators and therefore there is no insulation covering on its surface preventing heat transfer.
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