How to switch on-load voltage regulating transformer

On-Load Tap Changer (OLTC) is a kind of transformer device that can automatically or manually adjust the voltage when the load is running. Its main function is to change the transformation ratio by adjusting the number of turns of high voltage winding, so as to realize the adjustment of output voltage. This voltage regulation method is widely used in power system to maintain voltage stability and improve power supply quality. However, the switching operation of on-load voltage regulating transformer is not simply to change the tap position, but to follow strict operating procedures and safety measures. This paper will introduce the switching principle and operation flow of on-load voltage regulating transformer in detail.

I. Basic structure and working principle of on-load voltage regulating transformer

The core component of on-load tap-changer (OLTC) is on-load tap-changer. The switch can switch different taps of the high voltage winding without interrupting the load current, so as to realize voltage regulation. OLTC usually consists of driving mechanism, selector switch, transition resistor and switching contact. In the switching process, the transition resistor is used to limit the short-circuit current and arc generated at the switching moment to ensure the smooth and safe switching process.

Second, the basic process of switching

1. Judge the demand for voltage regulation:
The automatic voltage regulator in the power system will judge whether tap switching is needed according to the change of output voltage. When the voltage exceeds the set range, the control system will issue a voltage regulation command.

2. Start the switching procedure:
After OLTC control system receives the voltage regulating signal, it starts to execute the switching program. The drive mechanism drives the selector switch to move to the target tap position, and realizes the smooth transition of current through the transition resistor.

3. Complete the switch and confirm:
After the transition resistor is disconnected, the new tap is officially connected to the circuit. At this point, the system will detect the voltage level under the new tap to confirm whether the expected target is achieved. If it is not reached, it may be fine-tuned many times.

4. Record and alarm:
Every switching operation will be recorded in the control system, including switching time, current tap position, voltage change and so on. If the handover fails or is abnormal, an alarm signal will be triggered.

III. Matters needing attention and maintenance requirements

Although the on-load tap-changer can operate under live condition, the following points should be noted in actual operation:

-Switching frequency control: frequent switching will accelerate the mechanical wear of OLTC and shorten its service life. Therefore, the dead zone of voltage regulation should be set reasonably to avoid unnecessary switching.
-Regular maintenance inspection: including oil quality inspection, contact wear, lubrication of driving mechanism, etc., to ensure the reliable operation of OLTC.
-Handling of abnormal conditions: In case of switching failure, abnormal sound or abnormal temperature rise, the operation should be stopped immediately and overhauled.

IV. Conclusion

As an important voltage regulating equipment in modern power system, on-load tap-changer is very important for the safety of power grid. Understanding its switching principle and operation flow is not only helpful to improve the technical level of operation and maintenance personnel, but also helpful to ensure the efficient operation of power system. With the development of power electronics technology, OLTC will develop towards intelligence and automation in the future, which will provide strong support for building a more intelligent and reliable power grid system.