Cast Resin Transformer

en below in Fig 1.

Fig 1: Components of Cast Resin Transformer HIGH VOLTAGE WINDING The high-voltage coils are wound together with a high-grade conducting sheet from aluminum foils and double layers of insulating Mylar. The finished windings are then potted under vacuum up to the terminals. The external insulation is composed of a mixture of epoxy resin and quartz powder. LOW VOLTAGE WINDING It is also made from high quality Aluminum or copper foil. In between conductors pre-impregnated epoxy DMD (Dacron/Mylar/Dacron) insulation paper is used. When the finished coil is baked with high temperature, this DMD paper releases the epoxy and creates solid bonding with both side of the conductor. Thus it prevents from moisture, dusts and other contaminant to enter into the winding. Usually, the width of the aluminum foil is equal to the coil length. This considerably reduces the axial short-circuit forces. Fig 2: LV coils. MAGNETIC CORE High quality Cold Rolled Grain Oriented (CRGO) laminated Silicon Steel is used in this active part of the CRT and the stacks are placed in 5-Step-Lap mitered joints. As a result the magnetic core ensures minimum no-load losses. After stacking of the core, it is bound with heat shrinkable fiber glass tape bandages. On top of which two-part coating of epoxy paint ensures cohesion of the core laminations, protects against corrosion and further reduces noise emission [6]. Fig 3: The magnetic core. WINDING CLAMPS The coils, HV and LV are supported by resilient spacing blocks, which provide effective coil to coil and core to coil required distances. Moreover, these blocks ensure proper damping of the vibration and help reduce incumbent noises. Fig 4: Winding clamps. LV TERMINAL LV terminal of cast resin transformer is made of aluminum alloy. The thickness of aluminum depends on the current density of the service side; the higher the current density, the higher the thickness of terminals. Fig 5: LV terminal TAPPING LINKS HV tapping links enable the selection of the proper input voltages. It is an Off-Load tap changer i.e. tappings are configured while the transformer is in de-energized state. Tap-changing terminals are fitted with one link which ensures connection of one rating at a time. Usually the tappings allow ±2×2.5% of nominal voltage. Fig 6: Tapping links Characteristics of Cast Resin Transformers MOISTURE PROOF The complete casting of HV coils under vacuum prevents the penetration of moisture into the winding and the breakdown by ionization. Therefore, it is suitable for both storage and operation in adverse environments, including prolonged storage in up to 100% humidity and is capable of being energized immediately after such storage after drying. HIGH OVERLOAD CAPABILITY Based on the high thermal time constant factor of the windings, cast resin transformers can be overloaded for considerably longer periods of time than Liquid immersed or dry type transformers. It has a greater capability to withstand sudden momentary high overloads such as might be encountered in heavy traction or severe duty industrial applications. SHORT CIRCUIT RESISTANT The coil construction provides the highest mechanical withstand capability. The dynamic short circuit strength of a cast resin transformer is greatly superior to that of liquid-immersed or dry type transformers. In the event of a maximum short circuit, cast resin transformers are not endangered mechanically, due to the dense glass fiber filling and the adhesion of epoxy resin to the conductors. In case of a short circuit, the conductors heat up much faster than the surrounding insulation. Therefore only a strong glass fiber reinforced design, as found in cast resin transformers can prevent cracking of the coils. THERMAL SHOCK RESISTANCE Tensile and bending strength of glass fiber reinforced epoxy resin is appreciably higher than that of quartz powder filled resin which also has the disadvantage of becoming brittle and tending to crack when exposed to low temperature. Due to the complete combination of epoxy resin and glass fiber, even the worst temperature fluctuation will not induce the cracking of the coils in cast resin transformers. FIRE RESISTANT Cast resin transformers have an inherently safe characteristic of self fire-extinguishing and fire resistance. So there is no fear of spread of fire even if a fire takes place in near-by equipment. Therefore, CRT installation requires no additional measures for fire safety, which in itself is a major cost savings in terms of fire hazard maintenance. MAINTENANCE FREE Maintenance is almost completely eliminated. No checking of liquid level and no yearly dielectric test for moisture absorption is required. Due to the smooth coil surfaces, heavy dirt and dust build up is eliminated even under the worst circumstances. The recommended routine maintenance is an occasional visual or Infra-Red thermal inspection. COST SAVING If the advantage of cast resin transformers is taken into consideration at the planning stage, the overall costs of a power supply system can often be considerably reduced. They are sufficiently compact for convenient installation in a building where space is generally limited and have much smaller power loss than oil immersed and dry-type transformers. Totalcosts of ownership (TCO) are lower even though cast resin transformers may be more expensive than other transformers. Cost savings add low maintenance and longer operating life in all cases of cast resin transformer. Comparison of Oil Immersed Transformers and Cast Resin Transformer with Respect to Weight and Volume In the above figures, the red line indicates the oil type transformer and the green line indicates the cast resin transformer (CRT). It is evident that as the power rating goes up the volume and the weight of CRT is much more advantageous. Summary of Comparison between Oil Immersed and CRT Source: Energypac Cast Resin Transformers Cast Resin Dry Type Dual Voltage Distribution Transformer Cast Resin Dry Type Excitation Rectifier Transformer Transformers are electric equipment that changes the voltage and the current of electricity to facilitate its efficient transmission and distribution.  Transformers are commonly used at power generation facilities to increase voltage and to decrease current in order to transport electric energy across transmission lines. When the electricity reaches the end user, transformers are used to reduce voltage and to increase current to make the electricity suitable for general use.  The process of transforming voltage results in energy loss that is released in the form of heat and therefore transformers must contain effective cooling systems.  Transformers are differentiated by their cooling systems (this is one of several ways that the transformer industry classifies its products). Dry type transformers dissipate heat directly into the ambient air.  Liquid cooled transformers (e.g. oil filled transformers) dissipate heat into liquid mediums.  The cast resin transformer is a dry type transformer first developed in Germany in the 1960s as an alternative to oil-filled transformers.  In contrast to an oil filled transformer, which immerses coils in oil to absorb and disperse heat, the coils of a cast resin transformer are coated with epoxy resin, which is able to withstand temperatures as high as 188 degree Celsius.  Heat passes through the epoxy and dissipates into the surrounding air.  The cast resin transformer does not compete with oil filled transformers in all applications.  Most step up transformers at power plants that increase the voltage to hundreds of thousands of volts are oil filled transformers, because at such high voltages the amount of heat generated is more efficiently dissipated through a liquid medium.   However, many step down transformers located in the electricity distribution network and at the end user’s site are dry type transformers.  Certain wind and solar farms also use dry type transformers to step up electricity for transmission.  The cast resin transformer has several advantages over the oil filled transformer, including greater efficiency, less maintenance, greater fire resistance, and more environmentally friendly (the lack of cooling liquids eliminates the possibility of oil leaks).  While oil-filled transformers are still widely used in China and throughout the world, we believe cast resin transformers are increasing in popularity because of these advantages. In a cast resin transformer, the dry epoxy resin coating the transformer coils serve as the insulation medium between coils. To ensure effective insulation, appropriate precautions must be maintained to ensure that any moisture or condensation has been removed when the epoxy resin is cast.  Our cast resin transformers use four main types of insulation systems.  The insulation systems used are: 155 degree Celsius Class “F” per IEC60076 (International Electro technical Commission) and 180 degree Celsius Class “H” for the Chinese market and 150 and 185 degree Celsius per ANSI (American National Standard Institute), IEEE (Institute of Electrical and Electronics Engineers), and NEMA (National Electrical Manufacturers Associations) standards for the U.S. and North American markets. We manufacture cast resin transformers for a wide range of infrastructural and industrial applications, including – Cast resin dry type distribution (dual voltage) transformers, which are used in a wide range of infrastructure, commercial, and residential developments to step down the voltage of electricity from the electric grid to lower levels; Cast resin dry type power transformers, which are used in the electric grid to convert voltages; Cast resin dry type excitation rectifier transformers, which are used in power plants to deliver power to the excitation systems for electric generators; Cast  resin dry type traction rectifier transformers, which are used in subways and light rail systems to deliver power to rail electrification systems; Cast resin dry type transformers for variable frequency drives, which are used in wide range of industrial applications to deliver power to drive electric motors; Cast resin dry type transformers for marine applications, which are used on board ships or off shore platforms. Cast resin dry type transformers for wind applications, which are used in wind farms (either in or outside the tower) to step up voltage of the electricity generated for transmission in medium voltage electric grids; Cast resin dry type transformers for solar applications, which are used in solar farms to step up voltage of the electricity generated for transmission to medium voltage; Cast resin dry type transformers for Polycrystalline Silicon Reduction Furnace, which are used by manufacturers to deliver power to polycrystalline manufacturing facilities;  Cast resin dry type isolation transformers, which provide galvanic isolation to transfer power between two circuits not connected together and to protect against electric shock and suppress electric noise is sensitive devices; and Cast resin dry type transformers with amorphous alloy core, which are energy efficient and used in a wide range of infrastructure, commercial, and residential applications to step down voltage of electricity from the electric grid to lower levels. Source: http://www.jinpaninternational.com/cast-resin-transformers