training nbe auxiliarytransformer r0

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NEW BONG ESCAPE

Auxiliary transformers (3.5)

Oct. 2012

TRAINING MANUAL

Vol. III: BALANCE of PLANT


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New Bong Escape Balance of Plant

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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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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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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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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Design

LV connection to 400VAC switchgear by

copper busbar

HV connection to generator switchgear

by XLPE cable


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Outline and installation


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Outline and installation


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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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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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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

training nbe auxiliarytransformer r0

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