What is OLTC? What is it for, how does it work and for what purpose is it used?

OLTC is the abbreviation of the English expression On-Load Tap Changer and is the system that enables the transformer to change taps while under load. Briefly, the answer to the question of what is OLTC is; It is a special tap changer device that adjusts the voltage ratio by changing the winding connection point of the transformer during operation. In this way, voltage regulation can be made without cutting off the transformer's energy and the voltage level in the system is kept more controlled.

Voltage regulation is at the center of the question of what OLTC does. In electrical networks, the voltage level does not always remain the same due to load changes, line length, power flow and operating conditions. If these changes are not controlled, low or high voltage problems may occur on the end user's side. OLTC helps keep the output voltage within desired limits by gradually changing the transformation ratio of the transformer. For this reason, OLTC is a very critical equipment, especially in facilities where voltage quality is important.

Transformer windings have different tap points. The OLTC system changes the winding ratio by making a controlled transition between these step points. When the winding ratio changes, the voltage ratio of the transformer also changes. Thus, the voltage level on the secondary side of the transformer or on the system side to which it is connected can be increased or decreased. Since this adjustment can be made without de-energizing the transformer or disabling the load, OLTC is a much more functional solution than classical tap changers.

To explain the question of how OLTC works simply, the system is based on three main logics. First, which level to move to is chosen. Then, the transition from the current stage to the new step is made without suddenly cutting off the current and creating an uncontrolled arc. Finally, the mechanical movement that carries out this process is completed with the motor drive system. So OLTC is not just a switch; It is a special mechanism in which the selection, switching and drive system work together.

In classical OLTC designs, the selector switch and diverter switch are important main parts. In some designs, these structures may operate with a combined logic, and in others, they may operate with separate logic. While the selector side determines which tap point will be selected, the switching or diverter mechanism manages the transition under the load current. In addition, the motor-drive mechanism allows this movement to be carried out remotely or with local command.

OLTC is not the same as an off-circuit or de-energized tap changer. To perform off-circuit type tap change, the transformer must be de-energized. These types of structures may be simpler and require lower maintenance; However, it cannot regulate voltage during operation. OLTC, on the other hand, offers near real-time voltage regulation by changing the tap while the transformer continues to operate under load. This is a great advantage, especially in systems where network conditions are variable.

Therefore, OLTC is mostly used in transformers where active voltage regulation is required. Power transformers, some distribution transformers, special industrial systems and applications where it is important to keep the mains voltage within narrow limits are typical examples of this. Especially in large facilities where energy quality is important, the transformer becomes an equipment that not only converts energy but also manages the voltage level. OLTC is also at the center of this function.

One of the biggest benefits OLTC provides is business continuity. If the transformer had to be de-energized for every voltage setting, both processes and network management would become seriously difficult. Thanks to OLTC, the stage can be changed while the system is running and this process can be carried out automatically or in a controlled manner within certain limits. This helps create a more stable voltage profile on both the user side and the network side.

Modern OLTC systems may also include motor driver, position indicator, auxiliary contacts, remote control, automatic voltage regulation and alarm functions. Thus, the system ceases to be just a mechanical switcher and becomes part of the smart operating infrastructure of the transformer. Network management becomes more effective, especially when OLTC and automatic voltage control work together in substations.

OLTC is also considered one of the most moving and most stressed parts of the transformer. Because while the main body of the transformer operates largely static, mechanical movement and switching under current occur within the OLTC. For this reason, the need for maintenance in a transformer with OLTC naturally becomes more critical. Contact wear, mechanical fatigue, oil quality and drive system health can directly affect performance over time.

The terms OLTC and LTC are also frequently used in the field. In practice, these expressions often refer to the same concept, that is, a system that changes taps under load. However, there may be some sub-differences in technical details depending on the design and manufacturer approach used. However, when viewed at the blog level, the term OLTC is used to mean a voltage regulation system with a transformer that changes taps under load.

When selecting and evaluating OLTC, the voltage level of the transformer, current value, number of steps, step voltage, layout, maintenance approach and drive system should be considered together. Because this equipment is not just an accessory of the transformer, it is an active component that directly affects the voltage quality. An incorrectly selected or neglected OLTC can also negatively affect the overall performance of the transformer.

In summary, OLTC; It is a system that is of critical importance in terms of voltage regulation, allowing the transformer to adjust the voltage ratio by changing taps when under load. Selector allows adjustments without cutting off the transformer's energy by working together with the switching mechanism and motor drive structure. This is exactly the difference from off-circuit tap changers. If OLTC transformers, voltage regulation, transformer operating safety and maintenance plan will be evaluated together in your facility. transformer maintenance and testing, HV/MV testing, maintenance and repair and LV/MV/HV project design and consultancy services can support the technical decision process.