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NEW BONG ESCAPE
Auxiliary transformers (3.5)
Oct. 2012
TRAINING MANUAL
Vol. III: BALANCE of PLANT
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Auxiliary transformers
Contents
1.General introduction
2.Major technical data
3.Design
4.Outline and installation
5.Operation
6.Inspection and maintenance
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Auxiliary transformers
General introduction
1.New Bong Escape Hydropower Plant is equipped with two (2) sets of auxiliary transformers
of identical construction
2.The auxiliary transformers are of dry type design installed on mounting rails provided with
steel enclosure of IP20
3.The steel enclosures are painted in colour of RAL7032
4.The insulation class is F
5.The transformers are accessible via lockable swinging doors
6.The transformers are equipped with temperature monitoring and control device mounted on
the front panel of the transformers
7.The transformers are design for natural air cooling during operation
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New Bong Escape Balance of Plant
Auxiliary transformers
Major technical data
Rated voltage ratio: 112x2.5% / 0.4 kV
Rated capacity: 1600 kVA
Rated impedance voltage: 6%
Vector group: Dyn11
Temperature rise: 80 K
Cooling type: AN
Degree of protection: IP20
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Auxiliary transformers
Design
1.Each of the transformers has been dimensioned to carry full plant loads
2.High voltage side is made for connections of single-phase cables of 240mm2
3.Low voltage side is made for connections of copper busbar to 400VAC switchgear directly
4.Neutral point of low voltage windings grounded directly through a ring-type current transformer
for earth fault protection
5.NLTC of 2 x 2.5% on HV side
6.Arranged directly adjacent to the incoming feeder cubicles of 400VAC switchgear to facilitate
busbar connections
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New Bong Escape Balance of Plant
Auxiliary transformers
Design
LV connection to 400VAC switchgear by
copper busbar
HV connection to generator switchgear
by XLPE cable
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Auxiliary transformers
Outline and installation
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New Bong Escape Balance of Plant
Auxiliary transformers
Outline and installation
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New Bong Escape Balance of Plant
Auxiliary transformers
Operation
1.The two auxiliary transformers are energized from the busbars of generator
switchgear
2.Each of the transformers are fed from two feeders via cable in parallel
3.One of the two transformers will be connected to loads for normal operation
4.Design calculation shows that normal loading of the transformer shall be in the
range of 60 80% of rated capacity when all 4 units in operation
5.Over-capacity operation shall be avoided
6.Normal operation does not require attendance of any operational personnel
7.Core and winding temperature can be read at LED display on the transformerenclosure at LV side
8.Alarm signals of over-temperature is receivable at operator station in central
control room
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Auxiliary transformers
Inspection and maintenance
1.Daily visual inspection is required to disclose abnormal temperature, noise,vibration, and cleanness of the ventilation shield
2.Annual maintenance is sufficient if the transformers are operating in a dry and
clean environment, otherwise depending on the actual status the transformers
shall be maintained in an interval of 3 6 months
3.Before maintenance please make sure that the transformer is de-energized from
both HV side and LV side, and manually switch over the loads to the other
transformer.
4.The following work shall be done for maintenance:
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Auxiliary transformers
Inspection and maintenance
Cleaning of transformer enclosure, surface, inside enclosure, and ventilation shield
Visual inspection including surface damage on transformer body and crack of cast-
resin layer of the winding
Check of the electric-conductive elements and other parts free from dust, corrosion,
trace of carbonization and electrical flash-over
Please make sure that all tool and materials are removed from the transformer after
maintenance before putting the transformer back into operation
Please refer to NBE-203-08-201 for detailed instruction for handling, installation,
operation, and maintenance