When it comes to the power system, while we think about the enormous production benefits and living convenience it brings, we also pay great attention to its power and safety, after all, it is known as the "electric tiger". In the daily use of power transformers, "insulation" is related to its safety, and it is also the core to ensure the long-term stable operation of transformers. Whether it is the commonly used 500 kva power transformer or the more sealed hermetically sealed oil filled transformer, their insulation performance directly determines the service life and operational safety of the equipment.
I. Basic Concept of Insulation
Insulation, a term in physics, refers to the safety measure of using non-conductive substances to isolate or wrap charged bodies to protect against electric shock. The insulation of power transformers is to prevent current leakage and breakdown, ensuring the electrical safety and reliability of transformers. It involves the insulation between transformer windings, iron cores and other components and the ground, between windings of different phases, and between different voltage levels. For the 500 kva power transformer, a sound insulation design is the foundation for its adaptation to various power demand scenarios such as industry and commerce. The hermetically sealed oil filled transformer, with its sealed structure advantage, can better protect the internal insulation materials from external environmental erosion, further improving insulation stability.
II. Types of Insulation
The insulation of power transformers is divided into full insulation and graded insulation. Full insulation means that the entire winding is insulated to the same level, which is suitable for small transformers and low-capacity applications. The so-called graded insulation (also known as semi-insulation) means that the main insulation of the transformer winding near the neutral point area is lower than that of the input side. Transformers used in voltage levels of 35KV and below all adopt full insulation structure. Transformers with graded insulation are mainly used in large current grounding systems of power grids with voltage levels of 110kv and above.
Compared with full insulation, graded insulation can reduce the size of internal insulation, thereby reducing the size of the entire transformer, lowering the cost, and being more economical. However, it also has certain drawbacks, such as being less safe than full insulation. Whether it is the conventional insulation configuration of the 500 kva power transformer or the special insulation design of the hermetically sealed oil filled transformer, the scheme of full insulation or graded insulation will be reasonably selected according to the voltage level and use scenario of the equipment, balancing safety and economy.
III. Insulation Structure
From the internal and external perspectives, the insulation of transformers can be divided into external insulation and internal insulation, which applies to all types of power transformers, including 500 kva power transformer and hermetically sealed oil filled transformer.
Internal insulation refers to the insulation between different electronic components inside the transformer oil tank, mainly including winding insulation, lead wire and tap changer insulation, etc. These insulation parts are basically not affected by external conditions such as atmosphere, pollution, moisture and foreign objects. Internal insulation is further divided into main insulation and longitudinal insulation. Main insulation refers to the insulation between windings and the ground, between phases, and between windings of the same phase but different voltage levels. This is the most critical part of the internal insulation of the transformer, which directly affects the operational reliability and product cost of the transformer. For the hermetically sealed oil filled transformer, its sealed structure can effectively protect the internal insulation from moisture and impurities. The internal insulation design of the 500 kva power transformer focuses more on adapting to its medium and low capacity operation needs to ensure that the insulation strength meets the standard.
External insulation refers to the insulation bushings and air insulation outside the transformer oil tank, including the external insulation of the insulation bushings themselves and the insulation of the air gap distance between the insulation bushings and between the insulation tubes and the ground. The stability of external insulation is greatly affected by the environment, but it has a certain natural recovery ability.
IV. Insulation Methods and Materials
The insulation of power transformers usually adopts oil-immersed insulation, dry insulation, gas insulation and other methods. Oil-immersed insulation is mainly used in oil-immersed transformers, which can ensure the normal operation of transformers under high-voltage conditions, and has good moisture-proof, cooling, impact and arc-extinguishing performance. This is also the core insulation method of hermetically sealed oil filled transformer. Its sealed structure can prevent the insulation oil from oxidizing and deteriorating, extending the insulation life. Dry insulation and gas insulation are mainly used in dry-type transformers. Dry insulation has the advantages of not being easy to get damp, not easy to catch fire and easy to maintain, but it is not suitable for high-voltage environments. Gas insulation has low dielectric constant and good arc-extinguishing performance, but the cost is high and it is not easy to discharge gas in time.
In terms of insulation materials, there are solid materials and liquid materials. Solid materials such as insulating paper, corrugated insulating paper, Denison paper, Nomex paper, etc., have good thermal stability and moisture resistance, and are widely used in the internal insulation protection of various equipment such as 500 kva power transformer and hermetically sealed oil filled transformer. Liquid materials such as insulation oil need regular testing and maintenance of quality. Especially for hermetically sealed oil filled transformer, the purity of its insulation oil directly affects the insulation effect, so regular oil quality testing is required.
Insulation materials can also be divided according to heat resistance grades. The common grades are A, E, B, F and H, each of which has a corresponding limit allowable operating temperature. The maximum allowable temperature for Class A insulation is 105 degrees. The maximum allowable temperature for Class E insulation is 120 degrees. The maximum allowable temperature for Class B insulation is 130 degrees. The maximum allowable temperature for Class F insulation is 155 degrees. The maximum allowable temperature for Class H insulation is 180 degrees. Different types of transformers will choose the appropriate insulation material grade according to the operating temperature requirements. For example, 500 kva power transformer mostly uses Class F or H insulation materials to meet the heat resistance requirements of long-term stable operation.
V. Insulation Faults and Countermeasures
1.Insulation Aging
Transformer insulation aging is a complex and gradual process, which refers to the internal insulation materials of the transformer gradually losing their original mechanical strength and electrical insulation strength under the influence of various factors during long-term operation. The main causes of transformer insulation aging are as follows: improper moisture and heat insulation, chemical corrosion, long-term overload operation, transformer joint faults, electrical aging, pressure aging, etc.
To deal with transformer insulation aging, regular insulation resistance testing, dielectric loss factor testing, cleaning and keeping dry, regular oil change inspection, maintenance of cooling system, etc. should be carried out. For the 500 kva power transformer, regular insulation testing can timely find aging hidden dangers, avoiding equipment faults caused by insulation failure. Due to its sealed characteristics, the hermetically sealed oil filled transformer has a relatively slow aging speed, but it is still necessary to regularly check the quality of insulation oil and sealing performance to ensure the normal operation of the insulation system.
2.Insulation Moisture
Moisture in the insulation of power transformers is likely to cause interlayer or interturn short circuits of transformers, causing damage to the power system. The main causes of insulation moisture in power transformers are as follows: (1) Insulation moisture caused by poor transformer sealing (2) Insulation moisture caused by transformer quality problems (3) Insulation moisture during transformer transportation (4) Insulation moisture caused by transformer installation and maintenance (5) Insulation moisture due to long-term disrepair and aging of power transformers.
Therefore, in view of the possible insulation moisture problem of transformer insulation, the transformer insulation materials should be regularly inspected, and replaced in time if moisture is found. At the same time, avoid water and oil pollution during transportation and maintenance, and pay attention to the operation method during use to avoid insulation moisture caused by improper operation. Among them, the sealed design of the hermetically sealed oil filled transformer can effectively reduce the risk of moisture. For the 500 kva power transformer, special attention should be paid to insulation protection during transportation and installation to avoid moisture.
About JINSHANMEN TECHNOLOGY CO., LTD
JINSHANMEN TECHNOLOGY CO., LTD is a professional manufacturer of power transmission and distribution equipment, dedicated to providing high-quality and reliable transformer products and related solutions for global customers. The company mainly produces oil-immersed power transformers, dry-type power transformers, oil-immersed three-dimensional coiled power transformers, dry-type three-dimensional coiled power transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on-load capacity regulating power transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind energy box-type substations, high and low voltage switchgear and other transmission and distribution equipment. We have rich experience in the production and R&D of 500 kva power transformer and hermetically sealed oil filled transformer, focusing on optimizing insulation performance to ensure the safe and stable operation of equipment in various application scenarios.