Transformer windings can be either fully insulated or graded insulated. In EN 60076-3, these are referred to as homogeneous and non-homogeneous insulation, respectively. So do you understand what is full insulation and what is graded insulation?In this article, I will take you to make a brief understanding, hoping to deepen your understanding of transformer insulation.
The transformer is fully insulated
In transformers, complete insulation refers to the insulation design and insulation material selection of the windings and insulation structure of the transformer as a whole. Full insulation requires an insulating structure that completely covers the windings and provides sufficient electrical insulation to prevent current leakage and breakdown. Fully insulated transformers typically have higher voltage resistance and better insulation properties.
In a fully or uniformly insulated winding, the entire winding is insulated to the same level, determined by the voltage to which the entire winding is to be raised at the time of the test.
Graded insulation of transformers
The neutral point of the primary-side star-connected transformer may have graded insulation to optimize the design of the bushing and winding configuration. Due to the electrical characteristics of the neutral point, the level of withstand voltage for lightning impulses can be graded compared to the primary phase. Therefore, we can choose a lower insulating sleeve and can design the windings accordingly. This will optimize the overall transformer design. However, this needs to be agreed with the customer anyway.
Graded or uneven insulation allows for a more economical approach to designing the insulation structure of ultra-high voltage windings. Using this system, it is possible to recognize that such a winding will be connected to the star, and the star point will be firmly grounded. Therefore, the insulation at the ground end of the winding only needs to be designed to the nominal level.
Considerations when designing transformer insulation
When designing transformer insulation, the following points need to be considered:
Working voltage: First of all, you need to determine the rated working voltage of the transformer. Different operating voltages require the selection of different insulation materials and insulation structures to ensure that the insulation can withstand the required voltage levels.
Capacity and scale: For small transformers and low-capacity applications, a fully insulated design is sufficient;For large transformers and high-capacity applications, some places with low insulation requirements can be designed in a hierarchical manner depending on the cost.
Temperature rating: Transformers generate heat during operation, so insulation needs to be selected that can withstand the required temperatures. Different insulating materials have different temperature resistance, and it is necessary to choose the right material according to the working temperature of the transformer.
In many cases, new equipment purchased must run in parallel with equipment designed to earlier standards. In addition, the system itself is designed for such equipment standards. Since most transformers with two UHV windings, i.e. each winding at 132kV or more, tend to be autotransformers, this means that most dual-winding transformers have at most one winding with graded insulation, while many windings have both windings completely insulated.
The main reason for transformer insulation is to ensure the electrical safety and reliability of the transformer, and to avoid transformer failures and accidents caused by current leakage or breakdown.
In transformers, the insulation system plays a key role, so it is necessary to make a reasonable selection and design of the insulation system. However, in the specific design, the choice of insulation method will be determined according to the rated voltage of the transformer, the insulation requirements and the actual application requirements.
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