Oil-Immersed Transformers: Overview and Components
Oil-immersed transformers are essential devices in power systems designed to efficiently transform voltage levels for various applications. They play a pivotal role in both stepping up voltage for long-distance power transmission and stepping down voltage for local distribution, thus enhancing the overall efficiency and reliability of electrical power systems.
Components of Oil-Immersed Transformers
To improve cooling and insulation, oil-immersed transformers submerge their core and windings in transformer oil within a sealed oil tank. This design helps manage the thermal performance and longevity of the transformer. Key components of oil-immersed transformers include:
1. Active Part
· Core: Constructed from high-quality silicon steel laminations to minimize core losses.
· Windings: Copper or aluminum windings that transform electrical energy through electromagnetic induction.
· Insulation Structure: Provides electrical isolation between the core and windings.
· Leads: Connect the windings to the external circuits via bushings.
2. Oil Tank
· Body: Comprises the tank cover, tank walls, and tank bottom, providing a robust enclosure for the core and windings.
· Accessories: Include oil drain valves, wheels, oil sample valves, grounding bolts, and nameplates for operational management and maintenance.
3. Cooling System
· Radiators: Enhance the dissipation of heat from the transformer oil.
· Coolers: Provide additional cooling to maintain the optimal operating temperature.
4. Protection Devices
· Conservator: Accommodates oil expansion and contraction.
· Oil Level Gauge: Monitors the oil level within the tank.
· Safety Valve: Releases excess pressure to prevent tank rupture.
· Breather: Prevents moisture ingress into the oil.
· Temperature Sensors: Measure the temperature of the transformer oil and windings.
· Float: Detects the oil level in the conservator.
· Gas Relay: Detects gas accumulation within the oil, indicating potential faults.
5. Bushings
· High Voltage and Low Voltage Bushings: Provide insulated connections between the internal windings and external power circuits.
6. Tap Changer
· Off-Load Tap Changer: Allows manual adjustment of voltage taps when the transformer is de-energized.
· On-Load Tap Changer (OLTC): Enables automatic voltage adjustment without interrupting the transformer’s operation.
On-Load Tap-Changing Technology
On-load tap-changing (OLTC) technology is widely implemented in modern oil-immersed transformers to maintain stable voltage levels under varying load conditions. The OLTC switches between different voltage taps on the transformer coil while the transformer is under load, effectively adjusting the voltage ratio.
Traditional Mechanical OLTC:
· Operation: Uses a mechanical switch to change taps, which can create arcs and wear on the contacts.
· Challenges: Prone to contact erosion, slow switching times (typically about 5 seconds), and high maintenance requirements. These issues can lead to high fault rates and reduced reliability.
Innovations in OLTC:
To address the limitations of traditional mechanical OLTCs, several new technologies have been developed:
1. Improved Mechanical Type: Enhances traditional designs to minimize arc formation and mechanical failures.
2. Auxiliary Coil Type: Uses auxiliary coils to facilitate smoother tap changes.
3. Power Electronic Switch Type: Employs electronic components for faster, arc-free switching, improving both reliability and precision.
These advancements have significantly improved the performance and dependability of OLTC transformers in diverse power applications.
Advantages of Oil-Immersed Transformers
· Enhanced Cooling: The use of transformer oil ensures effective cooling, reducing thermal stress on the core and windings.
· Improved Insulation: Oil provides excellent electrical insulation, contributing to the overall safety and efficiency of the transformer.
· Extended Lifespan: Properly maintained oil-immersed transformers have a long operational life, making them a cost-effective solution for power systems.
· Versatility: Suitable for various applications including power generation, transmission, and distribution.
Conclusion
Oil-immersed transformers are vital for efficient voltage transformation and reliable power supply in modern electrical systems. Their advanced cooling, insulation, and tap-changing capabilities make them indispensable in both high-voltage transmission and low-voltage distribution networks. As technology evolves, innovations in tap-changing mechanisms continue to enhance the performance and reliability of these transformers, ensuring they meet the growing demands of power infrastructure.