Partial Discharge Characteristics Of Epoxy Resin Cast Cast Resin Transformer

Partial Discharge Characteristics of Epoxy Resin Cast Cast resin transformer

As a professional dry-type transformer manufacturer, Jiangsu Tianli Electromechanical Co., Ltd. has been in this industry for a long time. Everyone understands one thing: partial discharge (referred to as "PD") directly affects whether the transformer can operate stably for a long time and be reliable. Therefore, today we will specifically discuss what partial discharge in epoxy resin cast Cast resin transformer is and how to prevent and control it in practice.

Ⅰ. What is Partial Discharge (PD)

Partial discharge refers to the non-penetrating and intermittent discharge phenomenon that occurs in a certain local area within the insulation of electrical equipment or on its surface due to uneven electric field distribution. It does not mean that the entire insulation layer is directly punctured and completely short-circuited. Instead, it is caused by minor defects in the insulation material in some areas, such as a small air bubble inside, a bit of impurity mixed in, or an overly sharp edge of the conductor causing an excessively strong electric field. In these defective local small areas, the electric field is too strong, resulting in intermittent discharges. Eliminating such defects is a fundamental criterion for evaluating the manufacturing process level of a Cast resin transformer manufacturers.

Although this process is very small, it is accompanied by a series of detectable phenomena: there is a weak flow of electric charge, which emits high-frequency electromagnetic signals and ultrasonic waves that are inaudible to the human ear, and even generates a little light and trace amounts of gas.

We use a unit "pC" (picocoulomb) to measure the intensity of this discharge. The smaller this value, the better and cleaner the insulation inside the transformer. Because this indicator is so crucial, our company regards it as one of the lifelines for measuring product quality. Before each transformer leaves the factory, we conduct the most rigorous tests and controls on it.

Ⅱ. What is Partial Discharge (PD)

Epoxy resin cast Cast resin transformer are centered on "solid insulation + vacuum casting". Besides the previously mentioned points, the following key aspects should also be noted regarding their partial discharge (PD) characteristics:

1. What factors affect PD?

Material is fundamental: The cleanliness of the epoxy resin and the correct proportion of the curing agent directly determine the quality of the insulation. If even a tiny amount of moisture or impurities is mixed into the material, it will become a "weak point" after casting and curing, with a particularly strong electric field, which is prone to PD. Therefore, strict screening and control of raw materials is the first step for responsible Cast resin transformer manufacturers.

Process is crucial: The smoothness of the surface of the copper conductors in the coil and the uniformity of the thickness of the insulating layer are very important. If the conductors have burrs, they will be like needle tips and prone to discharge; if the insulating layer is uneven in thickness, the electric field will be chaotic, also easily causing PD.

Environment is a test: After the transformer is installed, if it is in a high-temperature, humid or dusty environment for a long time, it will accelerate the "aging" of its insulation. This will cause the originally small defects inside to grow larger, leading to an increasing PD level.

2. PD changes at different operation stages?

Initial stage: A well-manufactured new transformer should have a very small "initial PD value" (usually ≤5pC). If the PD exceeds the standard at this stage, it can basically be determined that there is a problem in the manufacturing process of the Cast resin transformer manufacturers, such as incomplete bubble removal during vacuum casting.

Normal operation: Under good conditions, a high-quality transformer will maintain a stable PD value for many years, with almost no increase. At this stage, the damage to the insulation caused by PD is very slow.

Start of aging: When the transformer has been in operation for many years and the insulation begins to age and become brittle due to the long-term effects of electricity, heat and the environment, the PD value usually starts to increase significantly. This is an important warning signal, indicating that internal defects may be expanding and immediate inspection and treatment are required.

3. Comparison of PD characteristics with oil-immersed transformers

The differences can be more clearly reflected through comparison, as detailed in the following table:

Ⅲ . Hazards of Partial Discharge

Jiangsu Tianli Electromechanical Co., Ltd. adheres to the partial discharge prevention and control concept throughout the entire process of "design - manufacturing - service", and the specific measures are as follows:

1. "Polishing" insulating materials like sandpaper: You can imagine those tiny discharges as countless high-speed "micro bullets". They continuously strike the epoxy resin, gradually breaking down the molecular structure of the material and gnawing out numerous microscopic pits on the insulating surface (this is called electrical erosion). Over time, the insulating layer will be worn thinner and thinner, and its strength will deteriorate.

2. Generating "thermal expansion and contraction", causing insulation "delamination": Each discharge creates a local hot spot, causing the surrounding resin to expand due to heat and then contract when cooled. This repeated "heat and cold" over a long period of time is similar to repeatedly bending a wire until it breaks, leading to the insulation layer around the conductor "delaminating" and creating tiny gaps. These newly formed gaps will become new discharge points, making the partial discharge more severe and creating a progressively worse vicious cycle.

3. Eventually threatening equipment and the power grid: According to statistics, approximately 30% of transformer failures are rooted in partial discharge. If left untreated, this slow destructive process will eventually lead to the complete breakdown of the insulating layer, causing a short circuit. The consequences could be the transformer burning out, power outages on the connected lines, and even fires due to high temperatures (although Cast resin transformer do not contain oil and are less prone to explosion, the high temperatures from internal short circuits are still extremely dangerous).

In summary: Partial discharge is a hidden and self-accelerating destructive process. It starts from a small weakness and continuously creates more weaknesses through "electrical erosion" and "thermal shock", potentially leading to catastrophic failures. Therefore, choosing a Cast resin transformer manufacturers that strictly controls materials, processes, and testing is fundamental to ensuring the long-term safe operation of transformers.

IV. Prevention and Control of Partial Discharge

Our company adheres to the concept of partial discharge prevention and control throughout the entire process of "design - manufacturing - service", with specific measures as follows:

First, in design, we eliminate problems from the root.

When designing coils, we insist on using round wires and polishing them to eliminate any "sharp corners" that may cause electrical sparks. At the same time, we use professional computer software to simulate the electric field distribution, precisely calculating the most suitable insulation thickness for each part to ensure uniform distribution of the electric field force and no particularly vulnerable "weak links". This is a true demonstration of our technical capabilities.

Second, in manufacturing, we ensure "zero defects" through meticulous craftsmanship.

This is the most critical production stage. We use extremely high vacuum (vacuum degree ≤ 10Pa) for casting to completely eliminate every tiny air bubble in the resin. On our automated production line, we precisely control the heating, holding, and cooling processes during resin curing to prevent invisible micro-cracks caused by uneven thermal expansion and contraction. Only in this way can we guarantee the perfect consistency of quality for each product.

Third, in operation and service, we work together with customers to ensure long-term safety.

We believe that a good transformer also depends on good usage and maintenance. We will clearly guide customers: keep the equipment surface clean to prevent dust and dirt; the operating environment temperature should not exceed 155°C and the humidity (relative humidity ≤ 85%). We are not just manufacturers, but also professional partners of our customers, providing specific maintenance suggestions and guidance to ensure the stable operation of the transformer for the next ten to twenty years.

our philosophy is: eliminate problems on the drawing board, solidify quality in the mold, and extend responsibility throughout the entire product life cycle.