S(Z)11-630~31500/35 series of On-Load Tap Changing Oil Type Transformer

10kV 20kV 35kV On-Load Capacity and Voltage Regulating Transformer (Oil-Immersed Type)

What is an on-load tap-changing transformer?

An on-load tap-changing oil-immersed transformer (OLTC Oil Type Transformer) is designed to maintain a stable output voltage while operating under load. During power transmission, impedance causes voltage drops that vary with user-side load. Combined with system voltage fluctuations, this can result in significant voltage variation. When these fluctuations exceed a set threshold, the on-load tap changer adjusts the transformer taps after a controlled delay to keep the output voltage stable without interrupting the power supply.

This type of transformer completes voltage conversion through its taps while the load is running, ensuring uninterrupted and precise voltage regulation.

Main Function in Power Systems

The primary task of the power transformer is to supply power directly to load centers. The primary winding connects to the main voltage network (220 kV and above) or regional grids (35–110 kV). This transformer provides both active and reactive power and typically features a large short-circuit impedance. Without an on-load tap changer, variations in regional load would cause the bus voltage to fluctuate accordingly.

Under the requirement of maintaining regional reactive power balance, the on-load tap-changing oil-immersed transformer adjusts its taps according to changes in load. Working together with parallel capacitors and low-voltage reactors, it ensures the user's power supply voltage stays within the qualified range.

Role of On-Load Voltage Regulating Transformer

1. Improve Voltage Qualification Rate

The voltage qualification rate is a key indicator of power supply quality. Timely on-load voltage regulation ensures stable voltage that meets the requirements of residential, industrial, and agricultural users. Oil-immersed on-load tap-changing transformers help maintain voltage within the allowable range during dynamic load variations.

2. Enhance Reactive Power Compensation and Increase Capacitor Utilization

Reactive power supplied by capacitors is proportional to the square of the operating voltage. When system voltage decreases, capacitor compensation weakens; when the voltage increases excessively, over-compensation may occur, elevating the terminal voltage of electrical equipment and potentially damaging insulation.

To avoid unnecessary equipment shutdowns, reverse reactive power flow, and capacitor waste, timely tap adjustments must be performed. The on-load tap-changing oil-immersed transformer adjusts bus voltage to keep it within the qualified range, ensuring effective reactive compensation.

3. Reduce Power Consumption

Power loss in a distribution network is minimized when equipment operates close to its rated voltage. The most economical solution is to use an on-load tap-changing transformer to maintain the substation bus voltage at an optimal level, reducing system losses and improving energy efficiency across 10kV, 20kV, and 35kV networks.

Performance parameters