Why can't dry-type transformers be stored and transported upside down for a long time?

Dry-type transformers are indispensable core equipment in modern power systems, and their safe and stable operation is directly related to the reliability of the entire power supply network. Unlike traditional oil-immersed transformers, the core and windings of dry-type transformers are not immersed in insulating oil, but rely on solid insulating materials such as air or epoxy resin for insulation and cooling. This structural feature determines that it has extremely strict requirements on posture during transportation and storage. Among them, long-term inverted storage and transportation must be avoided, which is an insurmountable red line to ensure the performance and life of the equipment.

I. Why are dry-type transformers "afraid" of being inverted and tilted for a long time?

Unlike oil-immersed transformers, dry-type transformers rely entirely on air convection for cooling, and their windings are the "heart" of the entire equipment. Prolonged inversion or tilting (usually the inclination must not exceed 15°~30°) will cause the following irreversible damage:

1. Looseness and displacement of winding mechanical structure

The low-voltage windings of dry-type transformers are mostly wound with copper foil or copper wire, and the high-voltage windings are cast with glass fiber reinforced epoxy resin. During the vacuum casting and curing process, extremely high mechanical compression forces are formed inside the windings.

• Risk point: When the transformer is inverted or severely tilted for a long time, the weight of the winding and core components will be concentrated on non-designed stress points.

• Consequences: This will cause the interlayer spacers to shift, axial fasteners (such as pressure nails, pull plates) to loosen, destroying the "overall tightness" of the winding. Once under the impact of short-circuit current during operation, winding deformation or inter-turn short circuit will easily occur.

2. Hidden microcracks in epoxy resin castings

Although epoxy resin has high hardness, its bending and tensile strength are relatively limited.

• Risk points: Long-term inversion will cause the insulation structure that was originally in a compressed state to be in a state of tension. Under the action of gravity, micro-cracks that are difficult to detect with the naked eye may occur inside the cast body.

• Consequences: These microcracks may appear normal during factory testing, but in long-term operation, moisture will penetrate deep into the insulation layer along the cracks. As time goes by, the amount of partial discharge will increase, eventually causing surface discharge or even breakdown accidents.

3. Core multi-point grounding and magnetic flux distortion

The iron core is the main magnetic circuit of the transformer and is usually fixed by threaded screws and clamps.

• Risk points: Long-term inversion may cause slight misalignment of the core laminations, or cause the core's grounding point (usually a single-point grounding) to come into contact with the clamp.

• Consequences: The core is grounded at multiple points, causing local overheating; at the same time, the magnetic circuit symmetry of the core may be destroyed, resulting in abnormal increases in no-load loss and no-load current, resulting in abnormal noise.

4. Damage to the fan and temperature control system

Dry-type transformers are usually equipped with axial cooling fans and temperature control boxes.

• Risk points: The circuit boards, relays and other components in the temperature control box, as well as the bearings and blades of the fan, are not designed to withstand the gravity of long-term inversion.

• Consequences: Prolonged inversion may lead to leakage of lubricating oil from the fan bearings, deformation of the fan blades, and detachment of wiring in the temperature control box, resulting in failure of the cooling system after operation.

II. Standardize the standard operating procedures for transportation and storage

In order to avoid the above hidden dangers, the following standards must be strictly implemented during the entire logistics cycle of dry-type transformers:

1. Transportation: Strictly observe the inclined red line

• Real-time monitoring: During long-distance transportation, a three-dimensional impact recorder should be placed on the top of the transformer. Once an inclination or severe impact exceeding the specified value (such as 30°) is recorded, unpacking and inspection must be carried out immediately.

• Correct binding: Use nylon slings or special steel wire ropes, and strictly follow the lifting points and center of gravity positions marked on the transformer shell for loading and unloading. It is strictly prohibited to bind or apply stress to the cover or clamps of the transformer.

2. Storage link: environment is better than posture

If the transformer needs to be stored for a long time (more than 3 months), in addition to maintaining a correct upright posture, environmental control is more critical:

• Moisture-proof measures: The biggest enemy of dry-type transformers is moisture. The storage location must be dry and ventilated. If it is stored outdoors, a rainproof shed must be built and the bottom should be raised by at least 200mm~300mm to prevent water accumulation on the ground and moisture return.

• Regular maintenance: During the storage period, the temperature control system should be checked regularly (such as once a month) to see if it is normal, and a heating dehumidifier (if equipped) should be put in to prevent condensation on the surface of the core and windings.

3. Inspection after the site is in place

After the transformer arrives at the site and is installed, the following inspections must be performed before power is transmitted:

• Appearance inspection: Check carefully whether there are cracks, damage or traces of creepage on the surface of the epoxy resin winding.

• Electrical testing: Be sure to conduct insulation resistance testing (using a 2500V megohmmeter) and DC resistance testing, and compare the test data with the factory test report to ensure that the data is within the allowable deviation range.

III. Conclusion

Dry-type transformers are high-precision electromechanical equipment, and the integrity of their insulation systems is directly related to the safe operation of the power grid. "Long-term inversion and improper storage are strictly prohibited" should not be just a warning slogan, but should become an ironclad operating rule engraved in the bones of logistics, warehousing and installation personnel.

Only by eliminating physical damage from the source can we ensure that this "power heart" can continue to deliver electricity stably and efficiently for decades to come.