If you’ve ever stood in front of a large power transformer at a substation, you might have noticed it’s far more than just a metal tank with coiled wires. Sure, the core and windings get most of the attention, but every transformer depends on a web of “other accessories” that keep it running safely, efficiently, and for decades. For my company, as a dedicated supplier of these often-overlooked parts, I’ve spent years learning exactly which materials make each accessory work—and why choosing the right ones makes all the difference for grid operators, industrial manufacturers, and infrastructure teams. Other Transformer Accessories
Let’s start with the most ubiquitous accessory no transformer can go without: bushings. Bushings are the insulated sleeves that let high-voltage current pass from the transformer’s windings to external power lines, while preventing current from leaking through the metal tank. A low-quality bushing can lead to flashovers, short circuits, or even catastrophic failure. So what are they made of? The core of a bushing is almost always a central conductor—typically a solid copper or aluminum rod, since those metals have exceptional electrical conductivity and can handle repeated thermal expansion and contraction from load fluctuations. That conductor is surrounded by insulation, and here, two materials dominate: porcelain and polymer composite. Porcelain bushings have been the industry standard for over a century. They’re made by firing a mixture of clay, quartz, and feldspar at extremely high temperatures, creating a hard, inert material that resists UV rays, moisture, and chemical corrosion. They’re cheap to manufacture for standard voltage levels, which is why you’ll still see them on older transformers. But polymer composite bushings have grown rapidly in popularity over the last 20 years, especially for urban substations where weight and space are critical. These use a fiberglass epoxy core (to add mechanical strength) wrapped in a weather-resistant outer layer of silicone rubber. Silicone repels water, so it’s far less prone to the tracking and surface damage that can cause insulation breakdown in damp environments, and it’s 30-40% lighter than porcelain, making it easier to install and transport. For the bushing’s top terminal, it’s usually a brass or aluminum fitting designed to connect directly to power lines, coated with a thin layer of tin to prevent corrosion and ensure a tight, low-resistance connection.
Next, consider transformer tap changers—those small, motorized or manual devices that adjust the number of turns in the windings to stabilize output voltage as load conditions change. A tap changer that fails mid-operation can throw entire neighborhoods or factories into dark or damaged equipment. The materials here are chosen for a balance of electrical performance, durability, and low friction. The main contact components, which carry the high current during tap changes, are made of silver-tungsten or copper-chromium alloys. Silver-tungsten is particularly effective because it has extremely high electrical conductivity, resists arcing (the tiny electrical sparks that happen when contacts separate), and doesn’t weld together even when exposed to high temperatures. The moving parts of the tap changer, like gears and linkages, are almost always case-hardened steel. Case hardening means adding a thin layer of carbon to the surface of the steel, making it hard and wear-resistant, while the core remains tough enough to absorb impact from repeated operation. We also use a small amount of nylon or PTFE (polytetrafluoroethylene, more commonly known as Teflon) for bushings between moving metal parts. These polymers have low coefficients of friction, so they reduce wear on steel gears and prevent the tap changer from jamming during voltage adjustments. For the tap changer’s motor housing, it’s a die-cast aluminum alloy—light, rigid, and resistant to the oil that transformers use for cooling and insulation.
Speaking of transformer oil, that’s another key accessory component, even though it’s often grouped separately from “solid” parts. Wait, no—let’s clarify: the cooling and insulation medium is a critical accessory, and its material science is fascinating. Mineral oil has been the standard for over a century, refined from crude oil to remove impurities that could cause electrical breakdown. It’s excellent at transferring heat from the core and windings to the transformer’s radiator fins, and its dielectric strength (the ability to resist electrical current flow) is far higher than air. But in recent years, natural ester oils (made from soybean or canola oil) have gained traction for environmentally sensitive areas, like urban substations near water sources, because they’re biodegradable and less flammable than mineral oil. Regardless of the type, the oil is stored in internal or external expanders—called conservators or gas cushions. Conservator tanks are made of carbon steel with a corrosion-resistant coating, usually a layer of epoxy paint, to prevent rust from oil and moisture exposure. For gas cushion conservators, sometimes you’ll find a flexible bladder made of nitrile rubber or EPDM (ethylene propylene diene monomer) to separate the oil from air, reducing oxidation of the oil over time.
Then there are the protective accessories, like pressure relief valves and burst discs. These are designed to automatically release excess pressure if the transformer’s internal temperature spikes—for example, if a short circuit causes the oil to vaporize. A burst disc is a simple, safety-critical part made of thin, high-strength stainless steel. We engineer the thickness of the disc so it ruptures at a precise pressure (usually around 15-20 psi above normal operating pressure), releasing the oil and gas before the tank can split. Pressure relief valves, which reset after pressure drops, use a brass or stainless steel valve stem, paired with a spring made of high-temperature alloy (like Inconel) that can handle repeated stress without losing elasticity. The spring is encased in a corrosion-resistant housing, and the valve seat is made of a rubber or Teflon gasket to ensure a tight seal when the valve is closed.
Let’s not overlook the small but vital sealing accessories, which are responsible for keeping oil in and moisture out. A transformer that leaks oil not only wastes a valuable resource but also risks insulation breakdown from water contamination. The most common seal material is EPDM rubber for gaskets between the tank and its cover, or between the radiator fins and the tank. EPDM is durable, resistant to transformer oil and UV light, and can flex over thousands of temperature cycles without cracking. For high-pressure applications, like sealing the central conductor of a bushing to the tank wall, we use silicone rubber or fluorocarbon (Viton) seals. Viton is especially useful for harsh industrial environments, as it resists chemical corrosion from pollutants and extreme temperatures. We also use thread seal tape made of PTFE for smaller connections, like those for pressure gauges or oil sampling valves, to ensure no oil leaks from threaded joints.
Another often-forgotten accessory is the transformer’s cooling fans and radiator fans. These are essential for large transformers in high-load conditions, helping to dissipate heat from the oil. The fan blades are made of glass-reinforced nylon or aluminum alloy. Glass-reinforced nylon is lightweight, moldable into aerodynamic shapes, and resistant to the vibration that comes with running a fan 24/7. Aluminum blades are sturdier for very high-load applications, though they’re slightly heavier. The fan motors are housed in die-cast aluminum, with windings made of copper wire (for high conductivity) and insulation made of polyimide film, which can withstand temperatures up to 200°C without breaking down. The fan’s mounting brackets are usually galvanized steel to resist rust in outdoor environments.
Now, you might be wondering: why does a supplier like me care so much about these materials? Because every transformer accessory is a tiny link in a huge, life-sustaining chain. A bushing made with cheap porcelain without proper glazing can fail in 5 years, instead of the expected 30. A tap changer with silver-tungsten contacts can handle 100,000 operations without wear, while a copper contact might fail in 20,000. For our customers—grid operators who need transformers to run 24/7, factories that can’t afford unplanned downtime, and infrastructure teams building for the next 50 years—the choice of materials isn’t just a detail; it’s about reliability, cost, and safety.
I’ve seen too many projects cut corners on accessory materials. A city installed low-quality polymer bushings on a new substation, and within three years, surface tracking from salt air caused two flashovers, leading to a 12-hour outage that affected 50,000 homes. Another factory used generic gaskets on their transformer, and a small oil leak led to water contamination, damaging the windings and costing $200,000 in repairs. That’s why we don’t just sell parts—we work with our clients to match the right materials to their specific needs. For a coastal substation, we recommend silicone-coated polymer bushings and Viton seals to resist salt corrosion. For a remote industrial mine with extreme temperature swings, we use case-hardened steel tap changers and Inconel springs that won’t lose elasticity in -40°C winters or 50°C summers.
Pole Mounted Transformer If you’re working on a transformer project—whether you’re replacing a single bushing for an older substation, upgrading tap changers for a new industrial facility, or building a substation for a residential development—we can help. Our team has decades of experience specifying materials that balance performance, cost, and longevity, and we manufacture or source all our accessories from certified, ISO-compliant suppliers to ensure every part meets international electrical standards. Don’t let a material choice derail your project’s reliability or budget. Reach out to our team to discuss your specific transformer accessory needs, and we’ll help you find the right components for your application.
References
- IEEE Standards Association. “IEEE Std C57.19.01-2020: Standard for General Requirements for Liquid-Immersed Transformer Bushings.” The Institute of Electrical and Electronics Engineers, Inc., 2020.
- National Electrical Manufacturers Association (NEMA). “NEMA TP 1-2019: Standard for Liquid-Immersed Transformers.” National Electrical Manufacturers Association, 2019.
- International Electrotechnical Commission (IEC). “IEC 60137: Insulated Bushings for Alternating Voltages Above 1000 V.” International Electrotechnical Commission, 2018.
- Transformer Maintenance Council. “Materials Selection for Transformer Accessories.” Electric Power Research Institute (EPRI), 2021.
- Society of Petroleum Engineers (SPE). “Natural Ester Fluids for Transformer Applications: Material Compatibility and Performance.” Society of Petroleum Engineers, 2020.
Jiangsu Yuantong Electric Co., Ltd.
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Address: No. 202, Qiaogang Road, Xicheng Subdistrict, Hai’an City
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