As a professional manufacturer of power transmission and distribution equipment, JINSHANMEN TECHNOLOGY CO., LTD 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. Among our core products, the hermetically sealed oil filled transformer, especially the 500 kva step down transformer model, is widely praised in the global market for its excellent sealing performance and reliable operation. This article will elaborate on the characteristics, installation and commissioning, as well as operation and maintenance of hermetically sealed oil filled transformers, to provide professional reference for industry peers.
1. Characteristics of Hermetically Sealed Oil Filled Transformer
Compared with ordinary transformers, the hermetically sealed oil filled transformer has obvious advantages in structural design and operation reliability, especially the 500 kva step down transformer produced by JINSHANMEN TECHNOLOGY, which integrates these advantages and is suitable for various complex working environments. The specific characteristics are as follows:
a. Elimination of Oil Conservator: The transformer adopts an expansion radiator. Since the expansion radiator can expand and contract with the change of transformer oil volume, it can effectively adjust the pressure and oil level inside the oil tank. This structural design simplifies the overall layout of the transformer and reduces potential leakage points, which is also a key design feature of the hermetically sealed oil filled transformer.
b. Full Sealing Structure: The tank cover and tank edge are welded together, realizing complete isolation between the transformer oil and insulating materials inside the transformer and the external atmosphere. This effectively prevents and slows down the moisture absorption and deterioration of transformer oil and insulating materials, thereby greatly extending the service life of the transformer. For the 500 kva step down transformer, this sealing structure ensures long-term stable operation in harsh environments such as high humidity.
c. Reliable Anti-Loosening and Sealing Measures: Special anti-loosening fastening measures are adopted inside the transformer, and high-quality oil-resistant materials and double sealing structures are selected for sealing. This ensures that the structural parts of the hermetically sealed oil filled transformer do not loosen during long-distance transportation and operation, with good sealing performance and reliable operation. Therefore, on-site installation without core lifting inspection, internal maintenance-free during normal operation, and minimal external maintenance are achieved, which greatly reduces the user's later operation and maintenance costs.
2. Installation and Commissioning
2.1 Handover Acceptance
After the hermetically sealed oil filled transformer is transported to the site, both parties shall conduct inspection and handover acceptance. The specific items include:
a. Check whether the data on the transformer nameplate is consistent with the requirements, especially for the 500 kva step down transformer, it is necessary to confirm the rated voltage, rated capacity and other key parameters.
b. Check whether the technical documents, drawings, test certificates, etc. are complete according to the list of factory technical documents.
c. Count whether the transformer main body and components are complete according to the disassembly list.
d. Check whether the transformer main body and components are damaged or have oil leakage.
e. Check the transformer oil level: Determine whether the transformer oil level is normal according to the display of the transformer oil level gauge. If the oil level gauge shows normal, it indicates that the transformer oil level meets the commissioning conditions.
When the transformer oil level gauge shows oil shortage, the following methods can be adopted: (1) Slowly open the plug on the upper part of the oil level gauge to release the residual gas inside as much as possible, and observe whether the oil level rises. If it rises to the qualified position, tighten the plug. (2) If the oil level does not rise after opening the plug of the oil level gauge, add transformer oil of the same model until the oil level is normal. Note: When opening the plug, it should be done slowly, otherwise oil injection may occur due to the pressure inside the oil tank.
2.2 Installation Test
a. The tap changer of the transformer is set at the rated position when leaving the factory. Before installation, the tap changer can be adjusted to the position suitable for the power grid voltage according to the requirements of the power grid voltage. No matter which position the tap handle is set to, it is necessary to ensure that the tap changer is accurately positioned in place. Pay attention to whether the indicated position of the operating mechanism is consistent with the actual position, and conduct tests such as measuring DC resistance and transformation ratio. This is particularly important for the 500 kva step down transformer to ensure that it can adapt to the local power grid voltage and stably output electric energy.
b. The measured values of insulation resistance, absorption ratio and dielectric loss provided by the product when leaving the factory are measured at 10℃~40℃ and relative humidity < 85%. Due to different temperatures during on-site testing, the resistance can be converted to the corresponding temperature during factory testing. The measured resistance value shall not be less than 70% of the factory value; The absorption ratio of power transformers of 35kV and above shall not be less than 1.3; The tgδ value shall not be greater than 130% of the factory value.
2.3 Transformer Hoisting and Installation
a. When hoisting the hermetically sealed oil filled transformer, the four lifting lugs on the tank wall must bear force at the same time, and the angle between the lifting rope and the vertical line must be < 30°. If this requirement cannot be met due to limited lifting height, corresponding effective measures shall be taken before hoisting. When hoisting, soft materials shall be padded at the contact between the lifting rope and the oil tank to prevent damage to the paint film, bushings and other components.
b. When hoisting the transformer main body, it is forbidden to use the four hanging plates on the tank cover. The hanging plates are only used for hoisting the transformer body and cannot be used for the overall hoisting of the transformer.
c. Avoid violent vibration during transportation and hoisting of the transformer, and the inclination angle shall be < 15°. Even for short-distance transportation, the main body shall be positioned stably and reliably, and effective fastening measures shall be taken to prevent accidents.
d. When installing the transformer main body, the foundation shall be firm to prevent resonance during operation, which will affect the sound level; The anchor bolts shall be fastened reliably without loosening; The entire oil tank must be reliably grounded through the grounding bolts.
e. If the transformer is equipped with a sudden pressure relay, an action test shall be conducted before installation, and it can be installed on the butterfly valve at the lower part of the oil tank and fixed with bolts only after passing the test. After installation, the butterfly valve must be opened to fill with oil, and the air nozzle must be opened to exhaust the internal gas (after oil is seen) and then sealed tightly. At this time, the oil level of the oil level gauge on the upper part of the transformer will drop, and the oil must be filled before sealing the air release and oil injection plug.
3. Operation and Maintenance
a. Before putting the hermetically sealed oil filled transformer into operation, check the action of each protection device (such as sudden pressure relay, pressure relief valve, signal thermometer, etc.), the oil level height of the oil level gauge, and whether the grounding is good and reliable.
b. When the transformer is in operation, the bulb (sensor) seat of the mercury thermometer and temperature indicator controller shall be filled with transformer oil.
c. The oil level indicator (oil level gauge) installed on the tank cover also serves to increase the oil level height, inject oil, vacuumize, replenish oil during operation, pressure test for leakage, etc., and is the only window leading to the outside world. To form a sealed state of the transformer, the sealing plug on the upper end cover of the oil level indicator shall not be easily opened at ordinary times to prevent water and moisture from entering the transformer.
d. The oil sampling valve installed under the wall of the transformer oil tank is used for sampling oil to test the electrical strength (breakdown voltage) of the oil. Before the hermetically sealed oil filled transformer is put into operation, take an oil sample to test the electrical strength of the oil. For transformers of 35kV and below, the oil breakdown voltage shall be ≥ 35kV; during the operation of the transformer, the oil breakdown voltage shall be ≥ 30kV.
e. If an abnormality occurs during the normal operation of the transformer, oil samples shall be taken for testing in a timely manner; if the oil sample test result is lower than the standard, the transformer oil shall be filtered or replaced.
f. After installing the pressure relief valve, carefully check the pressure plate on the upper part of the pressure relief valve. The pressure plate with marks must be removed before putting into operation; the shell and other parts of the relief valve shall not be disassembled at will, so as to avoid affecting the sealing performance and action sensitivity.
g. The transformer is not equipped with an oil conservator, and adopts a structure where the tank edge and the tank cover are welded. During operation, the change of transformer oil volume adjusts the oil level and pressure of the oil tank through the expansion of the expansion radiator. During normal operation, if the load is large, the ambient temperature is too high, or the temperature of the transformer when leaving the factory is low (such as winter), phenomena such as rising oil level of the oil level gauge, increased internal pressure of the oil tank, expansion of the radiator, and closing of the spring bowl may occur. It is allowed to operate with appropriate pressure relief (oil discharge) to restore the oil level to normal and open the spring bowl of the radiator. This operation is also applicable to the 500 kva step down transformer to ensure its safe operation under different working conditions.
h. Check the external air insulation distance before putting the transformer into operation, which shall not be less than the following requirements: for voltage levels of 3, 6, 10, 15, 35kV, the distance between bushings and between bushings and the ground shall be 60, 90, 125, 180, 340mm respectively.
i. The transformer switch is an off-load tap changer. When changing the tap voltage, the tap must be switched under no-load condition. It is forbidden to switch the tap when the hermetically sealed oil filled transformer is in operation with electricity.
j. When two transformers are operated in parallel, in addition to meeting the conditions for parallel operation of transformers, attention shall also be paid to: 1) The tap positions of the two transformers are consistent and in place; 2) The phase sequence is consistent to avoid reverse phase sequence marking; 3) Pay attention to the no-load closing interval time ≥ 5 minutes.
k. The transformer tank cover is of welded structure. No core lifting inspection is required before and during operation. The inside of the transformer is maintenance-free and the outside is minimal maintenance. However, if oil leakage is found at the high and low voltage bushings and the rotating shaft of the tap changer handle, it can be solved by tightening the fasteners or replacing the new sealing gasket.
l. The low-voltage outlet terminal of the indoor product is of epoxy casting structure, which should avoid ultraviolet radiation, rain and water immersion, and generally should not be stored outdoors. If stored outdoors, effective protective measures should be taken.
Conclusion
The hermetically sealed oil filled transformer, with its unique sealing structure and reliable operation performance, has become an important equipment in the field of power transmission and distribution. The 500 kva step down transformer produced by JINSHANMEN TECHNOLOGY CO., LTD is designed and manufactured in strict accordance with the above characteristics and technical requirements, ensuring excellent quality and stable operation. Mastering the correct installation, commissioning and operation and maintenance methods is the key to giving full play to the performance of the transformer. If you have more needs for hermetically sealed oil filled transformers and other power transmission and distribution equipment, please contact JINSHANMEN TECHNOLOGY, and we will provide you with professional products and technical services.