1 epoxy cast high voltage electronic transformer insulation design to consider the factors

1.1 insulation resistance

Insulation resistance to check the transformer insulation system of local defects and defects in general defects, is to verify the transformer insulation in normal, hot, high temperature and humidity and other environmental conditions, the degree of insulation reliability of an important technical indicators, but also determine the transformer electrical strength test The main reference.

1.2 Dielectric strength

The electrical strength is a key technical indicator of whether the transformer insulation system is subjected to transient overvoltage impingement capability and the presence of potential defects in the insulation system. In order to prove the reliability of the design, selection and manufacturing process of the transformer, it is necessary to carry out the main insulation reliability test.

1.3 partial discharge

Partial discharge is the local, non-penetrating discharge of the transformer coil, the insulation inside or between the two electrodes of the air under strong electric field. PD can make the transformer electrical insulation materials and mechanical properties of mechanical properties, is leading to the main reason for the aging of insulating materials, will directly affect the safe operation of the transformer and life. Therefore, in the design, the design should be taken from the insulation structure of the corresponding measures, not allowed within the insulation structure of a strong partial discharge.

1.4 heat aging and thermal life

Thermal aging and thermal life is to assess the transformer insulation material in the transformer operating temperature characteristics, the insulation, moisture, mechanical performance until the failure of the process of the important performance indicators. In order to slow down the thermal aging process of insulating materials, so that the transformer insulation has enough heat life, must be the transformer operating temperature to select the insulation material heat rating.

 

Insulation Design of Epoxy Casting High Voltage Electronic Transformer

2.1 Insulation structure of high voltage winding

(1) wound insulation. Due to the high voltage or high potential requirements of the transformer, the winding should adopt the heart type, single line package structure. When the system is wound, the segmented (positive and negative) winding system is used to reduce the voltage between the layers and the group, and the insulation (such as thickness) is reduced to achieve the purpose of reducing the transformer volume.

(2) early and insulated. The insulation distance of the winding die should be determined according to the winding operating voltage, the potential difference between the adjacent ones and the working environment of the transformer. If the initial arrangement of the state can not meet the insulation requirements, you can use reinforced insulation, turn, pole bending, high-voltage cable, countersink filling (nut) and wall (plate) and other ways to change his head position, Insulation performance, increase the electrical distance, to effectively prevent the purpose of creeping or flashover.
 

2.2 Insulation design using epoxy resin

As the transformer secondary to the primary and the core of the resistance test is often up to several thousand volts, tens of kilovolts, and its leakage current is very small, if the conventional insulation design and selection of the general insulation material is difficult to meet the requirements The The epoxy resin not only has good electrical properties, mechanical properties and process performance, or a flame retardant, flame retardant, highly adaptable to environmental conditions of the material. Data show that the epoxy resin curing products with excellent electrical insulation properties, breakdown voltage is generally 35 ~ 50 kV / mm, volume resistivity of 1013 ~ 1016Ω · cm. Epoxy resin products strong adhesion, high mechanical strength, shrinkage, size and stability. At room temperature or slightly after heating, it can become a mobile liquid, easy to mix with a variety of reagents to ensure the smooth progress of a variety of processing technology, it is widely used in transformers, especially high pressure or high potential transformer perfusion.
 

(1) Insulation thickness design. In practical applications, the relationship between the electrical strength and the thickness of the epoxy resin is non-linear, depending on the level of the process, the more mature empirical data is the theoretical value of 1/3 to 1/4. Due to the different working potentials of the primary and secondary windings of the transformer, the thickness of the epoxy casting is very different. The primary and secondary windings can be impregnated and poured separately, and the high-voltage winding should be vacuum-impregnated before pouring to improve Mechanical properties, electrical properties. However, if the primary winding outside the same process with the production of strip epoxy block positioning, and then bypass the secondary high-voltage winding, but also a one-time epoxy casting, to achieve time-saving, the purpose of saving.
 

(2) external insulation distance design. Practice has proved that the high-voltage transformer leads to the primary lead-out, between the core and its fasteners, along the epoxy resin solid surface or in the air will appear in the creepage or arcing phenomenon, which is outside the insulation Distance design and use of environmental conditions, in general good indoor environment conditions, the safety insulation distance is usually 400 V / mm. In addition, if the electric field of the dielectric surface is uniform, the insulation pitch of the arcing can be greatly reduced. Such as the formation of conductive coating or semi-conductive coating on the surface of the epoxy resin casting coil, covering the edge of the sharp edge, so that the insulating electrode and non-insulated electrode of the uneven electric field redistribution (cloth), in order to achieve the media (epoxy) Electric field uniform purpose. Can also use the same process epoxy resin plugging between the winding and the core of all air gap, can solve the joint parts of the local electric field caused by uneven corona.
 

The high-voltage winding of the transformer adopts epoxy resin as its basic sealing insulation, has good electrical performance, insulation performance and mechanical strength, the products are flame retardant, self-extinguishing, moisture, earthquake, fire, dust, safe and reliable.