Transformer Factory Acceptance Test (FAT)

Before a transformer is delivered to site, a Factory Acceptance Test (FAT) is conducted to ensure the transformer is safe, reliable, and complies with international standards such as IEEE and IEC. Transformer testing is commonly divided into three categories:

• Routine Test
• Type Test
• Special Test

Routine Test

Routine tests are performed on every transformer unit during manufacturing to verify its electrical and insulation performance before delivery.

The routine tests normally include:

1. DC Winding Resistance Test
   To verify winding resistance values and detect loose connections or winding abnormalities.
2. Transformer Turns Ratio (TTR) Test
   To confirm the transformer voltage ratio and winding configuration are correct.
3. Insulation Resistance (IR) Test
   To evaluate the condition of transformer insulation between winding and earth.
4. Tan Delta Test
   To assess insulation quality and dielectric losses within the transformer insulation system.
5. Power Frequency Withstand Test
   To ensure the transformer insulation can withstand specified power frequency voltage stress.
6. Induced Voltage Withstand Test
   To verify insulation strength between turns and between windings under overvoltage conditions.
7. No-Load Test
   To measure core loss and no-load current when the transformer is energized without load.
8. Load Test and Short Circuit Impedance Test
   To determine copper loss, impedance value, and transformer performance under loading conditions.

Type Test

Type tests are conducted on a prototype or selected transformer unit to verify the transformer design complies with applicable standards and performance requirements.

The type tests normally include:

1. Temperature Rise Test
   To determine transformer temperature performance under rated loading conditions.
2. Lightning Impulse Test
   To verify insulation strength against lightning surge voltages.
3. Switching Impulse Test (usually for EHV transformers)
   To assess transformer insulation capability against switching surge conditions.
4. Short Circuit Withstand Test
   To confirm the transformer can withstand mechanical and thermal stresses during short circuit conditions.
5. Sound Level Test
   To measure transformer noise level during operation.

Special Test

Special tests are performed based on customer requirements, project specifications, or special operating conditions to provide additional assurance of transformer quality and reliability.

A proper FAT procedure is essential to identify any defects or abnormalities before the transformer is delivered to site, ensuring safe and reliable operation throughout its service life.

The special tests normally include:

1. Magnetic Balance Test
   To evaluate magnetic circuit balance and detect possible winding faults.
2. Capacitance and Tan Delta Measurement
   To assess insulation condition and dielectric quality.
3. Sweep Frequency Response Analysis (SFRA) Test
   To detect winding movement, deformation, or transportation damage.
4. Zero Sequence Impedance Test
   To determine transformer impedance characteristics under zero-sequence conditions.
5. Harmonic Measurement Test
   To evaluate harmonic distortion generated by the transformer.
6. Vacuum and Pressure Leak Test
   To ensure transformer tank integrity and leak-free sealing performance.
7. Oil Quality Test
   To verify insulating oil characteristics such as dielectric strength, moisture content, and acidity.
8. Dissolved Gas Analysis (DGA)
   To identify possible internal faults by analyzing gases dissolved in transformer oil.
9. Partial Discharge (PD) Test
   To detect localized insulation defects within the transformer insulation system.
10. Functional Test of Protection Devices
    To verify proper operation of devices such as Buchholz relay, pressure relief device, oil level indicator, and temperature indicators.