The 330kV-220kV Power Transformer

1. Low loss, low noise

The core laminations are composed of imported high quality grain-oriented cold-rolled silicon steel sheets with chamfered joints and the joints are step-lapped with 5 steps, thus ensuring low loss and low noise. The inside of the tank is lined with magnetic and copper shields, measures have been take for metallic structural pares located in high magnetic field, to deduce stray loss and thereby the total load loss, and to relieve local overhearing. Performance standard of 330kV class transformers which designed and manufactured by our company, can reach GB 10-type or GB11-type, and the noise is much lower than GB.

2. Safe and reliable service

Reliability is the everlasting objective of our company, partial discharge of finished products are constantly kept below 100pC, ensuring that the transformers can be operated under long service voltage and occasional over-voltage without trouble. Low current density in winding conductor and appropriate cooling arrangement ensure that the winding temperature rise and top oil temperature rise are lower than that specified in the national standard by more than 5K and that the mechanical stress in winding conductor during short circuit does not exceed certain safe limit. Together with technological procedures during manufacture and other means to elevate mechanical strength, transformers can withstand server short circuit in all case during service.

3. Easy erection and maintenance

To minimize erection work at sit, transformers are so fabricated that lifting the active part out of the tank for inspection after arrival at sit is not mandatory. Beside, all components to be mounted on the transformer at site have been preassembled before dispatch, and all secondary wirings have been laid down into conduits on the transformer and connected to the terminals in the control cabinet or terminal box. Natural oil circulation and forced air cooling (ONAF) are generally adapted in our 180kV class transformers below 240MVA. 70% nameplate rating can still be achieved in case the fans are out of service. Little maintenance work is required for the cooling devices.

4. Careful fabrication

Vertical winding machines with tension device are used for winding, so that the windings can be wound more tightly and therefore mechanically strength as a whole. All insulation parts subjected to mechanical stress during short circuit, such as spacers in windings are made with T4 densified pressboard to deduce shrinkage. Drying process for the windings are carried out twice, once for ht individual winding, and again for the assembled phase block.After core and coil assembly, an additional vapor phase drying (VPD) is once more carried out to ensure that all insulation parts are thoroughly dried and no further shrinkage is possible to occur during service. All the high voltage terminals and nearby metallic structural parts are rounded up to prevent partial discharge. High voltage bushing terminals are contained with turrets, and kept concentric with the turret. All the leads are properly crimped and metallized to be rounded up. VPD process insures that the moisture content within the transformer is kept at a very low level, and the core and coil assembly is once more cleaned by condensed vapor flowing down the surfaces. The fabricated tanks are relived from welding stress and shot-blasted integrally, so as to be free form oil leakage trouble and to give the tank a clean, pleasant looking appearance.

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