List Of Mandatory Tests For Transformers

The following routine tests specified in IEC726 shall be carried out at the manufacturer’s works on each and every transformer:

a) Measurement of winding resistance

b) Measurement of voltage ratio and check of vector relationship

c) Measurement of impedance voltage (principal tapping), short circuit Impedance and load loss

d) Measurement of no-load loss and current

e) Separate source voltage withstand tests

f) Induced over voltage withstand tests

g) Partial discharge measurement (below 10 pC at measurement as per IEC 726)

Type Tests For Transformers

One transformer of each rating and voltage ratio shall be subject to the following tests as per IEC 726.

a) Lightning impulse test

b) Temperature rise test

c) Measurement of sound level

All costs for conducting the above tests shall be included by the contractor in the price or can be charged separately as agreed.

Test reports for climatic tests and environment tests on cast resin transformers as per HD 464 S1 shall be submitted.

Optional Additional Accessories can be provided with transformers as under:

  • 4 bi-directional rollers
  • 2 lifting lugs
  • 1 earthing terminal
  • 1 aluminum rating plate
  • 1 set of 3 PT 100 sensors
  • 1 digital thermometer
  • HV/LV cable boxes

Testing & commissioning of transformer

Schedule of Transformers Can be prepared as per below example:


1. Continuous rating at site conditions -1500kVA
2 Normal voltage ratio at normal tapping at full load 0.8pf 11kV/415V
3. Normal voltage ratio at no load 11Kv/433V
4. System highest voltage 12kV
5. Vector group Dyn11
6. Material of windings



7. Class of insulation (HV/LV) F
8. Permissible winding temperature rise by resistance at normal loading  under 50 degrees ambient








9. Impedance voltage 6.5
10. Power frequency withstand voltage (kV RMS) 38
11 Impulse withstand voltage 95
12. Maximum partial discharge when measured as per IEC 726 10 pC
13. No load loss at normal voltage and tapping (max)
14 Load loss at normal voltage and tapping (max)
15 Preset level of temperature monitoring system. Alarm trip 150 degrees

160 degrees

16 Enclosure-degree of protection IP31