Parallel operation of transformers?

Parallel operation of transformers refers to the operation of two or more transformers connected in parallel to supply power to a common load. Parallel operation of transformers is commonly used in power systems to achieve several goals, including redundancy, increased capacity, improved efficiency, and better voltage regulation.

When two or more transformers are connected in parallel, their primary and secondary windings are connected in parallel to a common busbar, which is then connected to the power source and the load. The connection of transformers in parallel is shown in Figure

(Parallel connection of transformers) 

The following are the key factors that should be considered when connecting transformers in parallel:

Transformer ratings and parameters

The transformers should have the same ratings and parameters, such as voltage ratio, phase angle, impedance, and winding configuration. The transformer parameters should be matched as closely as possible to ensure that the transformers share the load equally.

• Polarity

The polarity of the transformers should be the same. If the polarity is not the same, the transformers will not share the load equally, and the circulating currents will flow between the transformers, leading to overheating and damage.

• Vector group

The vector group of the transformers should be the same. The vector group refers to the phase displacement between the primary and secondary windings. If the vector group is not the same, the transformers will not share the load equally, and the circulating currents will flow between the transformers, leading to overheating and damage.

• Voltage regulation

The transformers should have the same voltage regulation characteristics. Voltage regulation refers to the change in secondary voltage with respect to the change in load current. If the voltage regulation characteristics of the transformers are not the same, the transformers will not share the load equally, and the voltage at the load will not be regulated properly.

• Short-circuit impedance

The short-circuit impedance of the transformers should be the same. Short-circuit impedance refers to the impedance of the transformer under short-circuit conditions. If the short-circuit impedance of the transformers is not the same, the transformers will not share the load equally, and the circulating currents will flow between the transformers, leading to overheating and damage.

• Tap settings

The tap settings of the transformers should be the same. Tap settings refer to the number of turns on the primary and secondary windings that are connected to the tap changer. If the tap settings of the transformers are not the same, the transformers will not share the load equally, and the circulating currents will flow between the transformers, leading to overheating and damage.

Advantages of Parallel Operation of Transformers

Parallel operation of transformers offers several advantages, including:

• Increased capacity

Parallel operation of transformers allows multiple transformers to be connected together to supply power to a common load, increasing the overall capacity of the system.

• Improved efficiency

Parallel operation of transformers allows the transformers to operate at a higher efficiency by reducing the load on each transformer. This reduces the losses in the transformers and improves the overall efficiency of the system.

• Redundancy

Parallel operation of transformers provides redundancy in case of a failure of one transformer. If one transformer fails, the other transformers can continue to supply power to the load, reducing the downtime and improving the reliability of the system.

• Better voltage regulation

Parallel operation of transformers allows the transformers to share the load equally, ensuring that the voltage at the load is regulated properly.

• Reduced circulating currents

Parallel operation of transformers reduces the circulating currents between the transformers, reducing the losses and improving the efficiency of the system.

Disadvantages of Parallel Operation of Transformers

Parallel operation of transformers also has some disadvantages, including:

• Increased complexity

Parallel operation of transformers increases

the complexity of the system. The installation, commissioning, and maintenance of parallel transformers require more resources and expertise than single transformers.

• Cost

Parallel transformers require more equipment, such as circuit breakers, switchgear, and control systems, which increases the cost of the system.

• Voltage imbalance

In a parallel operation of transformers, even a small imbalance in the transformer parameters, such as impedance or voltage regulation, can cause voltage imbalances between the transformers, leading to overloading and overheating of the transformers.

• Harmonics

Parallel operation of transformers can increase the level of harmonics in the system, which can cause interference with other equipment in the system and lead to power quality problems.

• Control and protection

Parallel operation of transformers require complex control and protection systems to ensure that the transformers share the load equally and operate within their safe limits.

Parallel Operation of Three-Phase Transformers

Parallel operation of three-phase transformers is similar to that of single-phase transformers. The primary and secondary windings of the transformers are connected in parallel to a common busbar, which is then connected to the power source and the load.

When connecting three-phase transformers in parallel, it is essential to ensure that the transformers are connected in the correct phase sequence. The phase sequence refers to the order in which the voltages of the three phases are applied to the transformer windings.

The phase sequence of the transformers can be determined using a phase sequence meter, which is connected between the transformers and the power source. The phase sequence meter indicates the sequence of the three-phase voltages, which should match the sequence of the transformer windings.

The parallel operation of three-phase transformers offers the same advantages and disadvantages as single-phase transformers. However, the parallel operation of three-phase transformers requires more careful consideration of the transformer parameters, such as the vector group, impedance, and voltage regulation, to ensure that the transformers share the load equally.

Conclusion

Parallel operation of transformers is an essential aspect of power system design and operation. It offers several advantages, such as increased capacity, improved efficiency, redundancy, and better voltage regulation. However, the parallel operation of transformers also requires careful consideration of the transformer parameters, control, and protection systems to ensure that the transformers share the load equally and operate safely.