1.Pressure Seal Test Requirements
According to GB/T 6451, distribution transformers must undergo a pressure seal test. The requirements for this routine test are as follows:
a) For transformers with a general structure (including sealed transformers with diaphragm oil cabinets), according to GB 1094.1;
b) For corrugated oil tanks (including those with elastic plate-type radiators), transformers rated at 315 kVA and below should withstand a test pressure of 20 kPa, while those rated at 400 kVA and above should withstand 15 kPa for 12 hours without leakage;
c) For sealed transformers filled with gas inside the oil tank, the upper oil level should withstand a test pressure of 60 kPa (excluding corrugated oil tanks) for 12 hours without leakage.

2.Pressure Deformation Test Requirements
According to GB/T 6451, distribution transformers must undergo a pressure deformation test. The requirements for this special test are as follows:
a) For transformers with a general structure (including sealed transformers with diaphragm oil cabinets), according to GB 1094.1;
b) For corrugated oil tanks (including those with elastic plate-type radiators), transformers rated at 315 kVA and below should be tested at a pressure of 25 kPa, while those rated at 400 kVA and above should be tested at 20 kPa for 5 minutes without damage and without unacceptable permanent deformation;
c) For sealed transformers filled with gas inside the oil tank, the test pressure is 70 kPa (excluding corrugated oil tanks), and it should withstand this pressure for 5 minutes without damage and without unacceptable permanent deformation.

3.Mechanical Strength Test Requirements
According to GB/T 6451, the oil tank of a distribution transformer must undergo a mechanical strength test. When applying a positive pressure of 103 kPa (hydraulic) to the transformer oil tank for 10 minutes, no cracking should occur. This is a special test.

4.Transport Impact Test Requirements
According to GB/T 6451, distribution transformers must undergo a transport impact test. This is a special test, and the method and requirements should be agreed upon by the user and the manufacturer.

5.Appendix GB1094.1-2013 Relevant Provisions:

Pressure Seal Test for Liquid-Immersed Transformers
The manufacturer of the transformer must conduct tests as per agreement to prove that the transformer oil tank will not leak during operation. If no agreement exists, a pressure test at 30 kPa above the normal liquid pressure should be conducted, maintaining 24 hours for transformers above 20 MVA or 725 kV; for transformers with lower ratings and voltages, maintain for 8 hours. A typical pressurization method involves using a liquid column or gas pressure on the oil cabinet. A visual inspection for leaks on the entire transformer follows. For tanks specially designed to accommodate liquid expansion (corrugated), agreements on leakage and full-life testing must be established.

Vacuum Deformation Test for Liquid-Immersed Transformers
This test is applicable to transformers designed for on-site vacuum filling with liquid. Generally, these transformers do not carry liquid during transport. When specifying deformation under vacuum and permanent deformation upon release of vacuum, measurements are required. The test should be performed on the complete transformer, including all parts requiring vacuum.

Before applying vacuum, suitable measurement reference points should be established, fixed to a structural element or floor, independent of the transformer, and as close as possible to the anticipated maximum deformation point. Measure and record the distance from the reference point to the tank wall. After achieving the required vacuum, measure the distance again. The difference in these measurements indicates the deformation under vacuum. After releasing the vacuum, measure again to determine the permanent deformation. Equivalent measurement methods can be used, including additional measurements on the opposite side of the transformer to compensate for tank displacement during the test.

Typically, expected deformation and permanent deformation under pressure should be calculated and announced by the manufacturer before testing. If values exceed expectations, re-testing is required to determine if the tank dimensions are stable. If unstable, remedial measures such as additional reinforcement of the tank should be taken.

Pressure Deformation Test for Liquid-Immersed Transformers
When deformation under pressure and permanent deformation after pressure release are specified, measurements are required. This test does not apply to tanks specially designed to accommodate liquid expansion (corrugated). The test should be conducted on a fully liquid-filled transformer, including all independent liquid-filled components. Unless specified otherwise, the test pressure should be 35 kPa above normal operating pressure. If the transformer is equipped with a pressure relief device, the test pressure should exceed the device's action pressure by at least 10 kPa. During testing, the pressure relief device should be blocked.

Note 1: The required overpressure can be conveniently achieved by adjusting the height of the liquid column (for example, by raising an independent oil cabinet with a crane). Before applying pressure, the oil level in the tank should be at the normal height. Establish appropriate reference points, fixed to a structural element or floor, independent of the transformer. These reference points should be as close as possible to the anticipated maximum deformation point, considering the influence of deformation. The distance from the reference point to the tank wall should be measured and recorded.

After applying additional pressure, measure the distance from the reference point to the tank wall again. The difference between the two measurements represents the pressure deformation. Equivalent measurement methods can be employed, including additional measurements on the opposite side of the transformer to compensate for displacement during testing. After reducing the pressure to its initial value, a third distance measurement should be taken. The difference between this measurement and the first one indicates the permanent deformation. Typically, the expected deformation and permanent deformation under pressure should be calculated by the manufacturer and announced prior to testing. If the limits are exceeded, re-testing is necessary to verify the stability of the tank dimensions. If unstable, remedial measures such as additional tank reinforcement should be taken.

On-site Vacuum Seal Test for Liquid-Immersed Transformers
This test applies to transformers designed for on-site vacuum filling with liquid, which generally do not carry liquid during transport. After site installation and before liquid filling, the ability to maintain vacuum and prevent air ingress in transformers requiring vacuum operation should be demonstrated as follows:
Apply the maximum vacuum level required for on-site operation. Once the vacuum gauge indicates the specified value, continue to evacuate for 2 hours or until a stable vacuum pressure value is achieved. Afterward, stop evacuating, maintain for 10 minutes, and record the initial vacuum pressure. Measure again after 30 minutes; the increase in pressure should be less than 20 Pa/h.