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Transformer Condition Assessment


Enhancing the life expectancy of a transformer is paramount to the cost effective running of any plant. Transformers are rated amongst the more expensive assets in their specific networks. Outages always cost the owner huge sums of money and should be avoided at all times. The transformer conditioning assessment offers a clear understanding of the conditions of the transformer fleet and accurate information on possible risks associated with every unit.

   Transformer remaining life analysis
   Fault and failure investigation
   Dielectric frequency response
   Conditioning assessment training
   Oil sampling training and oil flow measurement
   Transformer fleet screening
   Transformer advance analysis
   Temperature measurement
   Transformer assessment reports
   Transformer manufacturing training

It provides substance for asset management scenarios based on the company’s strategy and the condition of the fleet. It can define actions to be taken for each specific asset, considering technical and economic aspects.
It can implement defined actions by using efficient maintenance and repair technologies. Two stages for the risk analysis are proposed: Fleet Screening and Advanced Analysis (typically 10 - 20 % of fleet)

Fleet screening

Analysis of dissolved gases in transformer oil is being recognised worldwide as being an essential diagnostic tool for the early detection of incipient faults in transformers. It is an extremely cost effective method to monitor the condition of power transformers. The fleet screening steps give an initial good idea regarding the general condition of each transformer and possible needed maintenance actions such as drying, oil reclaiming, oil degassing and additional cooling. It also allows selecting a subset of the fleet that needs more advanced analysis.
Details of the Fleet Screening services rendered include:

1. Detailed visual inspections
   Status of gaskets, accessories and protection devices
   Reporting on findings and repair of defects

2. Oil sampling, analysis and reporting
   Chemical and physical status of the oil
   Dissolved Gas Analysis
   Furanic Analysis
   Predicted Degree of Polymerisation of the solid insulation

3. Thermal status of the transformer
   Cooling system inspection and verification by means of direct temperature recording of all fibre optic point measurements for a period to be mutually agreed upon (where applicable).
   Oil flow rate measurements can be taken and compared against design values (Oil Forced Air Forced (OFAF) Cooling only)

4. Thermal imaging of transformer
   Bushing connections
   Marshalling kiosk
   Tap changer motor drive cubicle
   Busbar connections

Advance analysis

The advanced analysis entails an evaluation of the main properties of the transformers using advanced diagnostic tests. The process also starts with the four steps of the fleet screening and then continues with:

5. Accessories verification and testing
   Buchholz
   Temperature indicators (OTI & WTI)
   Oil Level indicators
   PRV’s (Pressure Relief Valves)

6. Electrical tests
   Insulation resistance
   Turn to Turn Ratio (TTR)
   Winding DC resistance
   Capacitance and power factor/dielectric losses for bushings
   Dielectric dissipation factory (tan-delta) and capacitance measurement for windings

7. DFR (Dielectric Frequency Response) Analysis
   Status of the insulation system (oil-paper)

8. SFRA (Sweep Frequency Response Analysis)
   Mechanical status of the active part

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