How to Operate Oil – immersed Transformers in Parallel
As a respected supplier of oil – immersed transformers, I’ve witnessed firsthand the significance of parallel operation in many electrical systems. Parallel operation of oil – immersed transformers is a complex yet crucial process that can enhance the reliability, flexibility, and efficiency of electrical power distribution networks. In this blog, I’ll share some key insights on how to operate oil – immersed transformers in parallel. Oil Immersed Transformer
Understanding the Basics of Parallel Operation
Before delving into the operation process, it’s essential to understand why we parallel oil – immersed transformers. The core reasons include load sharing, increasing system capacity, and improving system reliability. When multiple transformers are connected in parallel, they can share the total load according to their rated capacities, reducing the stress on individual transformers. This not only extends the lifespan of the transformers but also allows for seamless expansion of the electrical system as the load demand grows.
However, for successful parallel operation, several conditions must be met. First, the voltage ratio of the transformers should be the same. A significant difference in voltage ratios can lead to a circulating current between the transformers, which not only wastes energy but also may cause overheating and damage. Second, the percentage impedance of the transformers should be similar. If the impedance values vary greatly, the transformers will not share the load proportionally, and one transformer may be overloaded while the other is under – utilized. Third, the phase sequence and the phase angle displacement of the transformers must be identical. Any mismatch in phase sequence or angle can result in large short – circuit currents, endangering the safety of the entire electrical system.
Pre – operation Checks
- Inspection of Transformer Parameters
- Thoroughly check the nameplates of the transformers to ensure that their voltage ratios, impedance percentages, and other key parameters meet the requirements for parallel operation. This step is fundamental as it forms the basis for proper load sharing and system stability.
- Use precision measuring instruments to verify the actual values of these parameters, as there may be slight deviations from the nominal values indicated on the nameplates due to manufacturing tolerances or aging.
- Visual Inspection
- Examine the physical condition of the transformers. Look for any signs of oil leakage, which can not only reduce the dielectric strength of the oil but also pose a fire hazard. Check the integrity of the transformer tank, radiators, and bushings for cracks or other damages.
- Inspect the oil level in the conservator. A low oil level may lead to inadequate cooling and insulation, while an overly high level may cause overflow during temperature variations.
- Electrical Testing
- Conduct insulation resistance tests on the windings of the transformers. Low insulation resistance may indicate moisture ingress or insulation degradation, which can compromise the safety and performance of the transformers.
- Perform a turns – ratio test to confirm that the voltage ratios of the transformers are within the acceptable range. This test helps to detect any internal faults or winding short – circuits that may affect the parallel operation.
The Parallel Connection Process
- Isolation and Safety Precautions
- Before making any connections, ensure that the transformers are completely isolated from the power source. This involves opening the disconnect switches and applying appropriate grounding to prevent accidental energization.
- Use personal protective equipment (PPE) such as insulated gloves and safety glasses to protect against electrical shock and other hazards.
- Connecting the Primary and Secondary Windings
- Connect the primary windings of the transformers in parallel. Make sure that the phase connections are correct, following the same phase sequence for all transformers. Incorrect phase connections can lead to short – circuits and equipment damage.
- Similarly, connect the secondary windings in parallel, maintaining the correct phase relationships. Use high – quality electrical conductors with sufficient cross – sectional area to minimize resistive losses.
- Initial Energization
- After the connections are made, perform a preliminary check of the entire system. Ensure that all connections are tight and there are no loose wires.
- Gradually energize the transformers, starting with a low – voltage test. Monitor the system for any abnormal currents or voltages. If any issues are detected, immediately de – energize the system and troubleshoot the problem.
Monitoring and Maintenance during Parallel Operation
- Load Monitoring
- Continuously monitor the load on each transformer to ensure that they are sharing the load proportionally. Use power meters and current transformers to measure the real – time load on each transformer. If one transformer is carrying a significantly higher load than the others, adjustments may be required.
- Analyze the load trends over time to predict future load demands and make necessary arrangements for transformer capacity expansion or load redistribution.
- Temperature Monitoring
- Keep a close eye on the temperature of the transformers, especially the winding temperature and the oil temperature. Overheating can indicate problems such as overloading, poor ventilation, or internal faults.
- Install temperature sensors and alarms to provide early warnings in case of abnormal temperature rises. Timely action can prevent severe damage to the transformers.
- Oil Quality Monitoring
- Regularly test the oil in the transformers for its dielectric strength, moisture content, and dissolved gas analysis (DGA). The oil plays a crucial role in insulation and cooling, and any deterioration in its quality can affect the performance of the transformers.
- Based on the test results, take appropriate measures such as oil filtering, replenishment, or replacement when necessary.
Troubleshooting Common Issues in Parallel Operation
- Circulating Currents
- If circulating currents are detected between the transformers, it may be due to differences in voltage ratios or impedance. Check the voltage ratios and impedance values of the transformers again and make adjustments if possible.
- In some cases, installing external impedance devices may be necessary to balance the circulating currents.
- Uneven Load Sharing
- Uneven load sharing can be caused by differences in impedance, incorrect connections, or malfunctioning protection devices. Verify the impedance values of the transformers and ensure that all connections are correct.
- Check the protection devices to make sure that they are functioning properly and not interfering with the load – sharing process.
- Overheating
- Overheating can be a result of overloading, poor cooling, or internal faults. First, check the load on the transformers and reduce the load if necessary.
- Inspect the cooling system, including radiators, fans, and pumps, to ensure that they are working effectively. If the problem persists, perform a detailed internal inspection to identify any possible faults.
Conclusion
Operating oil – immersed transformers in parallel is a technical and challenging task, but when done correctly, it can bring significant benefits to electrical power systems. By understanding the basic requirements, performing thorough pre – operation checks, following the proper connection process, and implementing effective monitoring and maintenance strategies, the parallel operation of oil – immersed transformers can be safe, reliable, and efficient.
Dry Type Transformer If you are in need of high – quality oil – immersed transformers or have any questions about their parallel operation, our team of experts is here to assist you. We offer a wide range of oil – immersed transformers with excellent performance and reliability. Contact us for professional advice and to discuss your procurement needs.
References
- "Power Transformer Engineering: Design and Application" by Leonard L. Grigsby.
- IEEE Standard C57.12.00 – Standard General Requirements for Liquid – Immersed Distribution, Power, and Regulating Transformers.
- "Electrical Power Systems Quality" by Roger C. Dugan, Mark F. McGranaghan, Surya Santoso, and Henry W. Beaty.
Deepwill International Technology Development (Jiangsu) Co., Ltd.
Deepwill International Technology Development (Jiangsu) Co., Ltd. is one of the most professional oil immersed transformer manufacturers and suppliers in China, featured by quality products and good price. Please rest assured to buy oil immersed transformer for sale here from our factory. Contact us for OEM service.
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E-mail: deepwill@deep-will.com
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