Oil Immersed Transformer Rectification Method

1. Core Role of Rectifier Circuits in Oil-Immersed Transformers

1. The oil-immersed transformer steps down high-voltage AC (e.g., 10kV) to low-voltage AC (e.g., 220V/380V) suitable for rectification.
2. The rectifier circuit (equipped with diodes or thyristors) converts low-voltage AC into DC.
3. A filter circuit (e.g., capacitor banks) reduces DC ripple, ensuring stable output for the load.

2. Three Common Rectifier Circuit Types: Characteristics & CHH Power’s Applications

(1) Half-Wave Rectifier Circuit

• Working Principle: Uses a single rectifier element (e.g., diode) to conduct current only during the positive half-cycle of AC, converting AC to pulsating DC.
• Advantages:
  • Extremely simple circuit structure, requiring only one rectifier element and minimal auxiliary components.
  • Low initial cost and easy maintenance.
• Disadvantages:
  • Low output DC voltage (average value ≈ 0.45×input AC voltage) and large ripple (unstable DC waveform), requiring additional filter components.
  • DC current flows through the transformer’s secondary winding, causing DC magnetization of the iron core—this increases the transformer’s volt-ampere (VA) rating relative to the actual DC power output (low energy efficiency).
• CHH Power’s Application Scope: Rarely used in mainstream industrial products due to inefficiency. Only applied in low-power, non-critical scenarios (e.g., small DC auxiliary power supplies for transformer monitoring systems) where cost is the primary concern.

(2) Full-Wave Rectifier Circuit

• Working Principle: Uses two rectifier elements and a transformer secondary winding with a center tap. Current conducts through one diode during the positive half-cycle and the other during the negative half-cycle, outputting continuous pulsating DC.
• Advantages:
  • Lower ripple factor than half-wave rectification (smoother DC output), reducing filter requirements.
  • Smaller transformer VA-to-DC power ratio (more efficient than half-wave), and DC magnetization of the iron core is nearly negligible (avoids core loss increase).
• Disadvantages:
  • The transformer’s secondary winding requires a center tap, increasing winding complexity and manufacturing costs.
  • Transformer utilization factor is lower than that of bridge rectification (only half the winding is active in each half-cycle).
• CHH Power’s Application Scope: Used in medium-power DC applications (e.g., 50–200kW industrial DC power supplies) where ripple requirements are moderate. CHH Power optimizes the transformer’s secondary winding design (e.g., using symmetric winding processes) to minimize tap-related efficiency losses.

(3) Bridge Rectifier Circuit (Most Widely Used)

• Working Principle: Uses four rectifier elements arranged in a “bridge” configuration. During both positive and negative AC half-cycles, two diodes conduct alternately, converting AC to continuous DC without a transformer center tap.
• Advantages (key reasons for CHH Power’s mainstream adoption):
  • Simple Transformer Design: No center tap required for the secondary winding, simplifying manufacturing and improving transformer utilization factor (up to 95%, higher than full-wave rectification).
  • Lower Reverse Voltage on Rectifiers: The maximum reverse voltage borne by each diode is half that of full-wave rectification (≈ 0.707×input AC peak voltage), extending rectifier lifespan.
  • No DC Magnetization: Symmetric current flow eliminates DC magnetization of the transformer core, reducing iron loss and ensuring stable transformer operation.
  • Low Ripple & High Efficiency: Ripple factor is significantly lower than half-wave and full-wave rectification, and the VA-to-DC power ratio is minimized (highest energy efficiency among the three types).
• Disadvantages:
  • Requires more rectifier elements (four vs. one/two), slightly increasing initial component costs.
• CHH Power’s Application Scope: The standard configuration for most oil-immersed rectifier transformers (e.g., 100kW–1MW industrial electroplating, high-voltage DC transmission auxiliary power supplies). CHH Power integrates high-reliability silicon rectifier bridges (with surge protection) into the transformer’s auxiliary cabinet, ensuring seamless matching and reducing on-site installation work.

3. CHH Power’s Optimization for Rectifier-Transformer Systems

1. Customized Transformer Design: Adjusts the transformer’s secondary voltage and winding impedance based on the rectifier type and load requirements (e.g., lower impedance for bridge rectification to reduce voltage drop).
2. High-Quality Rectifier Components: Uses industrial-grade rectifier diodes/thyristors (with temperature resistance up to 150°C) that match the oil-immersed transformer’s operating temperature range, avoiding premature failure.
3. Integrated Filter & Protection: Adds built-in capacitor filter banks and overcurrent/overvoltage protection modules to the rectifier cabinet, reducing ripple to ≤5% and ensuring safe operation under load fluctuations.