Low Voltage Transformer Bushings: For oil filled Transformers.

Low Voltage Transformer Bushings: For oil filled Transformers.

Within the broad landscape of electrical engineering, transformer bushings have a central role. These integral components are vital to all electrical apparatus, most notably transformers. This blog aims to deliver a thorough understanding of low voltage transformer bushings, their international standards, material selection, and possible drawbacks of certain decisions.

Defining Transformer Bushings

Transformer bushings act as the connecting medium between the transformer windings (encased within the transformer) and the external grid or cables. Their principal function is to insulate the current flowing through them from the body of the transformer, and they are designed to minimize power loss.

Standardizing Transformer Bushings

The efficacy and safety of transformer bushings are determined by their compliance with certain globally accepted international standards. These benchmarks, established by various international bodies, include IS 3347, DIN 42530, DIN 43539, and EN50386.

1. IS 3347: IS 3347 is a primary standard for transformer bushings as defined by Indian Standards. It outlines parameters for dimensions and other relevant technical specifications for both outdoor and indoor bushings utilized in transformers.

2. DIN 42530 and DIN 43539: DIN (Deutsches Institut für Normung) 42530 and 43539 are German standards that outline the requirements for transformer bushings under various circumstances. These standards enjoy wide adoption in European and other global markets.

3. EN50386: This European standard for transformer bushings encompasses both indoor and outdoor bushings' specifications. It sets the requirements for design, routine testing, sample testing, and much more in the domain of transformer bushings.

Voltage and Current Ratings of Low Voltage Bushings

These bushings are typically rated at the following current levels - 250, 630, 1000, 2000, 3150, 4000, and 5000 Amps, with voltage ratings of 1 kV and 3 kV.

Components for Oil filled Transformer Bushings

Insulator

Traditionally, porcelain has been preferred due to its outstanding electrical and mechanical characteristics. It's resistant to environmental and chemical factors like moisture, heat, and UV radiation. However, it's also prone to fragility and cracking.

Conductive Stem

The central stem which conducts the current is usually made of Brass for Ratings less than 1000 Amp and Copper for Ratings 1000 Amp and above. 

Supporting compoent.

These components are made of brass are used to center the stem in the center of the porcelain. 

Sealing Washer

Generally fitted at the top of the porcelain is used to prevent oil from within the transformer from leaking out. 

Gasket Selection

Gaskets are crucial for sealing the intersection between the bushing and the transformer tank. They should be capable of withstanding environmental conditions and the oil inside the transformer. Common gasket materials include rubber, non-asbestos fiber, and PTFE (Polytetrafluoroethylene) - known for their sealing capabilities, resistance to transformer oil, and durability.

Air End and Oil End Connections

When considering air end connections, options such as nuts, palm connectors, or bimetallic connectors are utilized. The choice is dependent on factors like current rating, installation ease, and required flexibility levels.

Conversely, for oil end connections, either a nut or spade type connection is typically used. Spade type connections allow for easier assembly and disassembly, while nut connections provide a more durable connection but may require more effort to install.

Commonly Asked Question about Transformer Bushings

Creepage Distance of Bushings

Advantages of In essence, creepage distance refers to the shortest path between two conductive parts, or between a conductive part and the bounding surface of the equipment, along the surface of the insulation. This concept is crucial as it helps prevent surface tracking, a type of electrical breakdown on an insulator that can lead to it becoming conductive.

Here's why creepage distance matters particularly for transformer bushings:

Transformer bushings are an integral part of any transformer, essentially providing an insulated passage for electrical conductors to pass through a grounded conducting barrier such as the case of a transformer. It's vital that these components are well-insulated to avoid the risk of electrical discharge and potential transformer failure.

Given the high voltages that transformers work with, there is a significant risk of electricity arcing (jumping across an air gap) between different parts of the device or between a device and grounded surfaces. This phenomenon is known as 'flashover'. A sufficient creepage distance is needed to prevent such flashovers.

The creepage distance in bushings is specifically designed to prevent this occurrence by ensuring there's enough insulative material between the conductive parts, hence reducing the risk of flashover. It is a safety measure to prevent electrical breakdown along the surface of the insulator due to environmental conditions such as pollution, humidity, and dust which can compromise the insulating properties of the bushing surface.

The required creepage distance for a particular application depends on a variety of factors, including the operating voltage and environmental conditions. For example, equipment operating in a high pollution or high humidity environment may require a longer creepage distance than equipment operating in a clean, dry environment.

In conclusion, the creepage distance in bushings plays a vital role in ensuring the safe and efficient operation of transformers, providing a safeguard against electrical discharge and potential equipment failure. 

Tin Plating of Transformer Bushings

Tin plating is a common technique used to enhance the performance and durability of both copper and brass. It involves coating the base metal (in this case, copper or brass) with a layer of tin, which offers a variety of benefits:

Corrosion Resistance: One of the main advantages of tin plating is its ability to provide excellent corrosion resistance. Tin is a noble metal that doesn't easily oxidize, which means it doesn't corrode as readily as many other metals. By plating copper or brass with tin, the underlying metal is protected from corrosive environments, extending its lifespan.

Low Contact Resistance: Tin plating helps maintain low electrical resistance, ensuring efficient electricity transmission. This is especially important in connectors and other components where good electrical conductivity is necessary.

Improved Aesthetics: Tin plating gives copper and brass a bright, silvery appearance, improving the aesthetic appeal of the base metal. It can also be matte or glossy, depending on the specific process used, allowing for aesthetic versatility.

Heat Resistance: Tin can withstand relatively high temperatures without melting or deforming, which means that tin-plated metals are suitable for applications that involve high heat.

In conclusion, tin plating can significantly enhance the functional characteristics of both copper and brass, making them more versatile, durable, and suitable for a wider range of applications.ference of 

Copper Stem Over Brass Stem in Ratings Above 1000 Amp

An essential factor to consider is the disadvantage of using a brass stem for bushings rated above 1000 Amps. The issue with brass lies in its lower conductivity compared to materials like copper. This results in increased resistance and subsequent heat generation. In high current applications (above 1000 Amps), this excessive heat can damage the bushing and shorten its lifespan.

Moreover, brass exhibits lower mechanical strength compared to copper, potentially leading to mechanical failure under high-stress conditions. Additionally, copper is a better conductor of electricity, leading to lower losses.

In conclusion, to ensure the optimal performance and longevity of transformer bushings, it's essential to understand the detailed aspects of bushings, their standards, material selection, and potential drawbacks such as the use of a brass stem in high current applications. Always ensure that your transformer bushings are made from suitable materials and adhere to the necessary standards to guarantee safety and reliability in your electrical systems.

Manan Shah

Partner 

Press-N-Forge

email : admin@shree-ji.com

A brief Note about our Company. 

Established in 1980, Press-N-Forge has been at the forefront of manufacturing high-quality transformer bushings for over four decades. With a deep commitment to quality, precision, and innovative design, the company has carved out a unique place in the electrical engineering sector.

Located in Mumbai, India, Press-N-Forge started with the vision of producing world-class transformer bushings to cater to the needs of the global electrical industry. The company has remained steadfast in its pursuit of this vision, continuously developing and improving their products to meet the evolving needs of their clients.

Renowned for their exceptional durability, reliability, and performance, Press-N-Forge's transformer bushings are used in a wide array of applications, serving a diverse customer base. Their products adhere to globally recognized standards, reflecting the company's commitment to maintaining international quality benchmarks. Over the years, the company has consistently demonstrated its ability to deliver products that withstand the test of time, even in the most challenging operational environments.

With a firm belief in innovation, Press-N-Forge invests heavily in research and development. Their state-of-the-art manufacturing facilities are equipped with the latest technology to foster design excellence and manufacturing efficiency. Through this commitment to technological advancement, the company ensures its products remain at the cutting edge of transformer bushing technology.

In summary, Press-N-Forge's legacy in manufacturing high-quality transformer bushings since 1980 is a testament to its dedication to quality, innovation, and customer satisfaction. As a trusted name in the industry, it continues to set the bar high, contributing significantly to the field of electrical engineering and beyond.