Installation And Commissioning Of Dry-type Transformers

Pre-installation Unpacking and Inspection

Check if the packaging is intact. After unpacking the 15kva dry type transformer , verify that the transformer nameplate data matches the design requirements, that all factory documents are complete, that the transformer is in good condition, and that there are no signs of external damage. Check for any displacement or damage to components, and any damage to electrical support parts or connecting wires. Finally, check for any damage or shortage of spare parts.

Transformer Installation

First, check if the pre-embedded steel plate of the 225 kva dry type transformer foundation is level. There should be no voids under the steel plate to ensure that the transformer foundation has good seismic and sound absorption performance; otherwise, the transformer noise will increase after installation. Then, use rollers to move the transformer to the installation position, remove the rollers, and precisely adjust the transformer to the designed position, ensuring that the installation levelness error meets the design requirements. Finally, weld four short channel steels to the four corners of the transformer base, i.e., on the pre-embedded steel plate, to prevent the transformer from moving during operation.

Transformer Wiring

When wiring, ensure the minimum distance between live parts and between live parts and ground, especially the distance from the cable to the high-voltage coil. High-current low-voltage busbars should be supported separately and should not be directly connected to the transformer terminals, as this will generate excessive mechanical tension and torque. When the current is greater than 1000A (such as the 2000A low-voltage busbar used in this project), there must be a flexible connection between the busbar and the transformer terminal to compensate for the thermal expansion and contraction of the conductor and to isolate the vibration of the busbar and the transformer. The electrical connections at each wiring point must maintain the necessary contact pressure. Elastic elements (such as disc springs or spring washers) should be used, and a torque wrench should be used when tightening the connecting bolts.

Transformer Grounding

The transformer grounding point is on the base of the low-voltage side, and a dedicated grounding bolt is provided, marked with a grounding symbol. The transformer grounding must be reliably connected to the protective grounding system through this point. When the transformer has an enclosure, the enclosure should be reliably connected to the grounding system. When a three-phase four-wire system is used on the low-voltage side, the neutral wire should be reliably connected to the grounding system.

Transformer Pre-Operation Inspection

Check all fasteners for looseness, ensure electrical connections are correct and reliable, and verify that the insulation distance between live parts and between live parts and ground meets specifications.  There should be no foreign objects near the transformer, and the coil surfaces should be clean.

Transformer Pre-Operation Commissioning

(1) Check the transformer's transformation ratio and connection group, measure the DC resistance of the high and low-voltage windings, and compare the results with the factory test data provided by the manufacturer.

(2) Check the insulation resistance between coils and between coils and ground. If the insulation resistance is significantly lower than the factory measured data, it indicates that the transformer is damp. When the insulation resistance is below 1000Ω/V (operating voltage), the transformer must be dried.

(3) The test voltage for the withstand voltage test should meet the specifications. When performing the low-voltage withstand voltage test, the temperature sensor TP100 should be removed. After the test, the sensor should be promptly returned to its original position.

(4) When the transformer is equipped with a fan, the fan should be powered on and its normal operation ensured.

Trial Operation

After a thorough pre-operation inspection, the transformer can be energized for trial operation. During trial operation, special attention must be paid to checking the following points:  Any abnormal sounds, noise, and vibration; any abnormal odors such as burning smell; any discoloration caused by local overheating; and whether ventilation is adequate.

In addition, the following points should also be noted:

First, although single phase dry type transformer has strong moisture resistance, because it is generally an open structure, it is still susceptible to moisture, especially since 500kva dry type transformer produced in my country generally has a lower insulation level (lower insulation class). Therefore, the 30 kva dry type transformer can only achieve high reliability when operating at a relative humidity below 70%. The 50 kva dry type transformer should also avoid prolonged shutdowns to prevent severe moisture damage. When the insulation resistance value is below 1000/V (operating voltage), it indicates that the transformer is severely damp and trial operation should be stopped.

Secondly, the 3000 kva dry type transformer used for voltage boosting in power plants is different from oil-immersed transformers and should not be operated with the low-voltage side open-circuited to prevent overvoltage from the power grid or lightning strikes on the lines, which could lead to transmitted overvoltage and insulation breakdown of the three phase dry type transformer . To prevent the dangers of transmitted overvoltage, a set of overvoltage protection surge arresters (such as Y5CS zinc oxide surge arresters) should be installed on the 300 kva dry type transformer voltage busbar side.