SIGMA has an excellent structure for the maintenance of power and distribution transformers. The equipments received for repair go through careful evaluation to identify the cause of the failure. Such information is then passed on to the customer for the customer to evaluate and authorize the maintenance.
The equipments get the appropriate treatment so it operates in accordance with the current norm. If necessary, it is redesigned to meet the required specifications.
The transformers tank also goes through a careful evaluation, verifying points of leakage, rust and other malfunctions. All tanks get the appropriate treatment to remove the impurities and rust from its surfaces, for this, a modern blasting process with steel shot is used. Next, the internal and external painting of the tank is performed, according to the client’s specification. If the tank is not in usable conditions, it is replaced by a new tank.
The oil from the transformer passes first by screening.Then, an oil sample is sent for PCB analysis. The approved oil goes through the regenerating process so that it recovers its characteristics of purity and insulation. After this process other analysis are performed to ensure that the oil has the ideal operating conditions.
The active part of the transformer undergoes a temperature controlled drying process in order to remove all the moisture contained in it. A high precision megohmmeter is used to verify and guarantee the necessary insulation. The insertion of the insulating oil is performed in a vacuum chamber, which facilitates that penetration of the oili the active part of the transformer, as it removes air bubbles trapped in the coils, which can cause partial discharges when ionizing during the applied voltage test. The vacuum tends to reduce the air moisture before filling the transformer. All transformers undergo the routine tests listed below. The tests accompany the equipment.
• Winding resistance;
• Insulation resistance;
• Transformation ratio;
• Excitation current and no-load losses;
• Short circuit voltage and load losses;
• AT and BT applied voltage;
• Induced voltage;
• Sealing and pressure resistance;
• Routine tests on the insulating oil, PCB content and corrosive sulfur.