Transformer tap changers are essential devices that are responsible for adjusting the voltage levels in power transformers.
This blog aims to provide an in-depth understanding of the role of transformer taps, their significance in maintaining optimal power system performance, and their functionality within power transformers.
What Are Transformer Voltage Adjustment Taps?
Transformer voltage adjustment taps are specific connection points located on the transformer windings. They are designed to enable small, incremental adjustments to the input voltage rating of the transformer. These adjustments are essential for ensuring that the transformer can maintain the correct secondary voltage, even when the primary voltage deviates from its expected level.
In an ideal scenario, a transformer would not require taps, as the supplied voltage would consistently align with the transformer’s rating. However, in reality, variations in primary voltage are quite common, often due to factors such as voltage drop along lengthy distribution lines or significant power consumption by end-users.
The presence of transformer taps offers a practical and effective solution, allowing utilities and end-users to fine-tune the input voltage as necessary, thereby ensuring a stable and reliable output voltage.
How Do Transformer Taps Work?
Transformer taps enable the adjustment of voltage by changing the turn ratios between the primary and secondary windings. When the secondary voltage needs to be increased, the turn ratio is decreased by using fewer turns on the primary winding.
Conversely, to decrease the secondary voltage, more turns are used on the primary winding to increase the turn ratio. This adjustment process can be carried out using either a load tap changer (LTC) while the transformer is supplying load current, or a no-load tap changer (NLTC) which requires the transformer to be de-energized.
Types of Transformer Taps
Transformer taps are vital for stabilising voltage in electrical power systems by adjusting input voltage to ensure consistent output, even when the primary supply fluctuates. Understanding the different types of transformer taps and their specific applications helps manage power distribution and enhance transformer performance.
The various types of transformer taps are:
1. Dry Type Transformer Taps
In dry-type transformers, adjustments to the taps are typically made manually. This involves using jumper cables to connect to different tap positions. Although the process is simple, it necessitates the transformer to be disconnected from its power source for safety reasons.
2. Liquid-Filled Transformer Taps
In liquid-filled transformers, the tap-changing mechanism is fully immersed in oil. This design choice helps in making the mechanism more space-efficient. The adjustment of tap positions is carried out mechanically using an external rotary switch. This particular design is prevalent in larger MVA transformers, which are typically liquid-filled.
Tap Changing Mechanism
The process of tap changing involves adjusting the transformer’s turn ratio to ensure that the secondary voltage remains at the correct level, even when there are fluctuations in the primary voltage. For instance, if the primary voltage falls below the transformer’s rated level, a tap changer can be employed to modify the turn ratio, thereby increasing the secondary voltage to the required level.
Calculating Tap Positions
Assume a transformer has a 100% tap rating of 13,800V:480V. The percentage tap for different voltages can be calculated as follows:
- For a +2.5% tap, the primary voltage is 14,145V.
- For a -2.5% tap, the primary voltage is 13,455V.
The turns ratio for each tap is calculated by dividing the rated primary voltage by the secondary voltage. For instance, the turns ratio for a +2.5% tap is 14,145V/480V = 29.47. To find the resulting secondary voltage for an actual primary voltage of 13,450V, divide 13,450V by the turns ratio (29.47) to get approximately 456V.
Types of Tap Changers
Tap changers are important devices in transformers that enable the adjustment of voltage levels to maintain a stable and reliable output despite fluctuations in the input supply.
The types of Tap Changers are:
1. Load Tap Changers (LTC)
Load tap changers allow for tap adjustments while the transformer is energised and supplying load current. They are commonly found in liquid-filled transformers and are suitable for applications with frequent voltage fluctuations.
2. No-Load Tap Changers (NLTC)
No-load tap changers require the transformer to be de-energized before making adjustments. These are more common in dry-type transformers and in situations where voltage adjustments are infrequent.
Tap Configurations
Tap configurations are fundamental to the functionality of transformer tap changers, determining how voltage adjustments are implemented to achieve desired output levels. These configurations specify the number of tap positions available and the incremental voltage changes they provide.
Common configurations include:
Five-Position Tap Changers
Most distribution transformers have five tap positions, with two taps above and two taps below the nominal rating, each at 2.5% increments. These taps allow for full-capacity operation at the adjusted voltages.
Seven-Position Tap Changers
Some transformers have seven tap positions, providing more flexibility with two taps above and four taps below the nominal rating, each at 2.5% increments. This configuration allows for a supply voltage within 5% above and 10% below the nominal rating.
Practical Application and Importance
Transformer taps and tap changers are essential for ensuring a stable voltage supply in power distribution networks. By allowing for adjustments at the point of power consumption, it helps to maintain the desired secondary voltage, preventing potential damage to sensitive equipment and ensuring efficient operation of electrical systems.
In practical applications, transformer taps are used to compensate for voltage drops in long distribution lines and fluctuations in power consumption. This capability is essential for utilities and end-users, enabling them to manage voltage levels effectively at the point of consumption, thus enhancing the overall resilience and performance of the power distribution network.
Final Thoughts
Understanding and implementing transformer tap changers is essential for optimal voltage regulation and power system efficiency. Utilising solutions such as Universal Power Transformers (UPT) for selecting the ideal transformer, along with advanced tools like transformer tap changers and voltage adjustment mechanisms, can significantly reduce the risk of operational failures. Proper management and precise adjustments of transformer windings ensure efficient power distribution and stable voltage levels, enhancing overall system performance. This strategic approach not only minimises maintenance costs and prevents equipment downtime but also contributes to a more sustainable and cost-effective energy infrastructure.
