Before to energize the transformer a visual check to make sure that not any external object has got inside the transformer, especially in correspondence with LV connection and in cooling ducts. If the transformer has been stored for a long time it’s necessary to control the absence of condensation or dust. Please use dry compressed air jets and dry cloth just in case.


After the transformer positioning into transformer room please perform the following mechanical checks:

  • Proper transformer grounding check torque
  • Proper Insulating and safety distances check
  • Proper tightening of transformer and HV and LV terminals and the tap changer.

Here follows the table of the suggested tightening torque parameters:


Commissioning TAB 1


Commissioning TAB 2

kg/m = (N/m) / 9,81.


Before HV and LV connection to HV and LV transformer’s terminal the following electrical checks have to be performed:

  • Check of tap changer links, all the links have to be in the same position
  • If the transformer have more than one primary voltage it’s necessary to control that it has be connected on the same available in the network. If not the tapping links have to be adjusted accordingly.
  • It is necessary to control that all the protections are properly installed and adjusted with correct parameters for a prompt action of system protection.
  • Accessories operative verification.
  • We recommend to control the windings isolation between them and against ground through a megaohmmeter performing the measurements at a voltage of 2.500V. The correct values to be obtained are the following: a) Measurement between HV windings against LV windings and ground > 20 MΩ; b) Measurement between LV windings and ground > 10 MΩ

If the measured values are lower than what above mentioned the transformer have to be cleaned and dried in accordance with the suggestions provided before and repeat the test. Please do not hesitate to contact our technical department if the problem cannot be solved.

After transformer energization, but before LV load connection, the output voltage has to be verified to make sure that the value 
is in line with the expected rating output voltage. If the values are different from what expected please de-energize the transformer and, after all the safety check are performed, adjust the tapping links in the proper way to obtain the expected voltage level in accordance with the following diagram.

Messa in servizio Img 1

The following formula can be used to understand the proper link to be selected:

(Vmis / Vnom – 1) x 100 = Tap changer stage to be selected (%)

Vmis is the measured voltage on LV side and Vnom is the transformer rated voltage.

The transformer majority is provided with ± 2 X 2,5 % tap changers but other configurations are available.

In case of double primary voltage transformer (for example 10.000-20.000V) two tap changers are available and both of them must be located in the same link position!

In case the tap changer is different from what above described or in case of unexpected measured voltage level, please contact our technical department.