How does an oil-filled transformer work?
Oil-filled transformers are vital components in electrical power distribution systems, serving to step-up or step-down voltage levels as required for efficient transmission. The functioning of these transformers relies on the principles of electromagnetic induction. Within the transformer, alternating current (AC) passes through the primary winding, creating a magnetic field that induces a voltage across the secondary winding, transferring power from one circuit to another. The core of the transformer, typically made of laminated steel, helps concentrate and direct the magnetic flux, enhancing efficiency.
Power transformer is one of the core equipment of power network, so its stable and reliable operation will play a very important role in the safety of power system. However, due to the limitations of design and manufacturing technology, process and operation and maintenance level, transformer failures still occur from time to time, especially in recent years, people have gradually paid attention to the transformer near or export short circuit (hereinafter referred to as export short circuit) failure, which greatly affects the safe and stable operation of the power system.
Power transformer installation
The installation of a power transformer is a crucial process that demands meticulous planning and execution to ensure optimal performance and safety. Site selection plays a pivotal role, considering factors such as accessibility, proximity to load centers, and environmental considerations. Prior to installation, thorough inspections of the transformer, accessories, and ancillary equipment are imperative to identify any defects or discrepancies. Rigorous adherence to manufacturer specifications and industry standards is paramount during the installation process to mitigate risks and ensure compliance with regulatory requirements.
(1) Equipment and material preparation
The transformer shall be equipped with a nameplate. The nameplate should indicate the name of the manufacturer, rated capacity, primary and secondary rated capacity, primary and secondary rated voltage, current, impedance, voltage and connection group and other technical data. Transformer capacity, specifications and models must meet the design requirements. Accessories and spare parts are complete, and there are factory certificates and technical documents. Section steel: Various specifications of section steel should meet the design requirements, and there is no obvious corrosion. Bolts: Galvanized bolts should be used, with corresponding flat washers and spring gaskets, except anchor bolts and anti-shock device bolts. Other materials: welding rod, anti-rust paint, blending paint, etc. should meet the design requirements, and have product certification.
(2) Operating conditions
Construction drawings and technical data are complete and correct; The basic construction of the civil works has been completed.
(3) Operation technology
Equipment point inspection: Equipment point inspection shall be carried out jointly by the installation unit, the supplier, and the representative of the construction unit, and make a good record. According to the equipment list, construction drawings, and technical documents, check whether the specifications and models of the transformer body and accessories meet the requirements of the design drawings. Whether it is complete, missing or damaged. Transformer body appearance check no damage and deformation, paint intact without damage. Insulation porcelain parts and epoxy resin castings have no damage, defects and cracks. Transformer secondary handling should be carried out by lifting industry, electrician cooperation. It is best to use car crane hoisting, but also can use chain hoisting. When handling the transformer, pay attention to protect the porcelain bottle, it is best to cover the high and low voltage porcelain bottle with a cloth box or carton, so that it is not damaged. Transformer handling process, there should be no impact or serious vibration, the use of mechanical traction, traction point should be below the center of gravity of the transformer, to prevent tilt, transport tilt Angle should not exceed 15 degrees, to prevent internal structure deformation. Before handling or loading and unloading of large transformers, the direction of the high and low voltage side should be checked to avoid difficulties in changing the direction during installation.
Transformer commissioning
Commissioning marks the transition from installation to operation, encompassing a series of tests and procedures to validate the functionality and performance of the transformer system. This phase involves conducting insulation resistance tests, winding resistance measurements, and polarity checks to verify the integrity of the transformer windings and connections. Additionally, oil sampling and analysis are conducted to assess the condition of the insulation and detect any potential abnormalities. Commissioning also includes the calibration of protective relays and control systems to safeguard the transformer against overloads, faults, and other operational anomalies.
(2) transformer transmission debugging operation
1. Transformer no-load input impact test. When the transformer is put in for the first time, it can be closed by full pressure impact, and it can generally be put in by the high voltage side during impact closing. After the transformer is powered for the first time, the duration should not be less than 10min, without abnormal conditions.
2 transformer no-load operation inspection method is mainly to listen to the sound. When it is normal, it emits a buzzing sound, and when it is abnormal, the following conditions occur: When the sound is relatively large and uniform, it may be that the applied voltage is relatively high; When the sound is loud and noisy, the core may be loose; There is a squeaky discharge sound, possibly the core and casing surface flashover; There's a popping sound, possibly a core breakdown.
3. Transformer commissioning and operation. After no-load impact test, it can run in no-load for 24 ~ 28h, and can run with half load if it is confirmed that there is no abnormality. After the half-load commissioning operation of the transformer meets the safety operation regulations, the full load commissioning operation is carried out. Transformer full load commissioning operation for 48h, again check the transformer temperature rise, oil level, oil infiltration, cooler operation. After passing the full load test, the transfer procedures can be handled before it can be put into operation.
Transformer acceptance
Upon successful completion of commissioning, the transformer undergoes acceptance testing to ascertain compliance with project specifications and regulatory requirements. These tests encompass a comprehensive assessment of electrical, mechanical, and operational parameters to validate the transformer's performance under varying load conditions. Any deviations from specified tolerances are thoroughly investigated and rectified to ensure the reliability and longevity of the transformer system. Once accepted, the transformer is integrated into the power distribution network, contributing to the seamless and efficient delivery of electrical energy to consumers.
Acceptance plan: the transformer starts to live, 24h after no abnormal situation, should go through the acceptance procedures; The following materials and documents shall be handed over at the time of acceptance: design change certificate; Product specifications, test reports, certificates and installation drawings and other technical documents; Installation check and adjustment records.
The test adjustment and body inspection results of the power transformer and its accessories must conform to the provisions of the construction code. The surface of high and low pressure porcelain is strictly prohibited from defects such as crack damage and enamel damage. The installation position of the transformer should be accurate, the surface of the body is clean and clean, and the paint is complete. Transformer and line connection shall meet the following requirements:
1. The connection is tight, the locking device of the connecting bolt is complete, and the porcelain casing is not subject to external force.
2. Connect the neutral wire to the line segment of the grounding device along the device body and secure it securely.
3. The connecting wire between the accessories of the body has a protection tube, the protection tube and the junction box are fixed firmly, and the box cover is complete.
4. The bus leading to the transformer and its support, wire protection tube and neutral line should be easy to disassemble, and do not hinder the movement of transformer maintenance. The thread of each connecting bolt leaks out 2 ~ 3 nuts, the color of the protection pipe is consistent, and the anticorrosion of the support is complete.
5. The transformer and its accessory shell and other non-live metal parts shall be grounded and meet the relevant requirements.
Conclusion
Power transformer is in an extremely important position in the power system, its operation, overhaul and maintenance is directly related to the economic benefits of the power supply enterprise, social image and the quality of the user's electricity, related to the power quality of the majority of users, but also related to the safety of the entire system. Therefore, it is highly concerned by the power system. In the actual operation and maintenance process of the site, due to the use conditions, operating environment, operating cycle and maintenance personnel's sense of responsibility and skill level, the actual reflected operating level is very different.
