Parallel Connection of Transformer | Parallel Transformer | Parallel Transformer Load Sharing

Parallel connection of transformer is Connecting the secondary windings of two transformers in parallel can be done to increase the available current capacity. When two transformers are connected in parallel, their secondary windings are connected together, and the resulting voltage at the output is the same as the voltage of each individual transformer.

However, there are some important considerations that must be taken into account when connecting transformers in parallel, particularly in terms of their impedance matching and current sharing.

One important consideration is to ensure that the two transformers have the same voltage ratio, to avoid any potential problems with unbalanced voltage output. Additionally, the transformers should have the same impedance, or at least a similar impedance, to ensure proper current sharing between them. If the impedance is not matched properly, one transformer may take more of the load and overheat, while the other may be underutilized.

To achieve proper current sharing, it may be necessary to install current sharing resistors or current transformers to monitor the load on each transformer and adjust the current sharing as needed. This will help to ensure that the load is evenly distributed between the transformers, and that each transformer operates within its safe operating limits.

It's also important to note that connecting transformers in parallel can increase the overall size and cost of the system, as well as introduce additional complexity and potential points of failure. As such, it's generally recommended to use a single transformer with sufficient capacity to meet the load requirements, rather than connecting multiple transformers in parallel.

Parallel Transformer

A parallel transformer is a transformer that is designed for parallel operation. Parallel transformers are constructed with multiple primary and secondary windings that are connected in parallel. The primary and secondary windings of parallel transformers are wound with the same number of turns and have the same voltage rating. The construction of parallel transformers ensures that the transformers share the load equally and operate efficiently.

Load Sharing in Parallel Transformers

Load sharing in parallel transformers is the process of distributing the load among the transformers connected in parallel. The load sharing in parallel transformers is essential to ensure that each transformer shares an equal portion of the load. The load sharing is achieved by using load sharing transformers or by using auto-transformers. Load sharing transformers are special transformers that are designed to ensure that each transformer shares an equal portion of the load.

Understanding Transformer Impedance

Impedance, in general, is a measure of opposition to the flow of alternating current in an electrical circuit. It consists of two components: resistance (R) and reactance (X). While resistance opposes the current flow due to the conductor's physical properties, reactance arises from the interaction between inductance and capacitance in the circuit.

Transformer impedance is the ratio of the transformer's winding impedance to its rated voltage. It represents the total opposition to the flow of electrical current through the transformer. The impedance is expressed in ohms and is usually given as a percentage of the transformer's rated voltage.

The transformer impedance is significant as it affects the power system's voltage regulation, fault levels, and transient stability. It also determines the amount of current flowing through the transformer during normal operation and under fault conditions. Therefore, understanding transformer impedance and its calculation is essential for proper system design, protection, and operation.

Role of Impedance in Transformers

Impedance in transformers affects various aspects of their operation. It determines the voltage drop under load conditions, the ability to regulate voltage, and the level of losses. Understanding and calculating impedance accurately is crucial for designing transformers that meet specific requirements and perform optimally.

Importance of Accurate Transformer Impedance Calculation

Impact on Transformer Performance

Accurate calculation of transformer impedance is crucial for ensuring optimal performance. Impedance affects voltage regulation, load capacity, and overall system stability. By having precise impedance values, engineers can design transformers that operate efficiently and reliably.

Efficiency and Losses

Transformer impedance directly influences the losses occurring in the system. Higher impedance leads to increased copper losses and reduced overall efficiency. By accurately calculating impedance, engineers can minimize losses and enhance energy efficiency.

Voltage Regulation

Transformer impedance significantly affects voltage regulation. It determines the voltage drop across the transformer under load conditions. With accurate impedance calculations, engineers can design transformers that maintain stable voltage levels, preventing voltage fluctuations and ensuring the proper functioning of connected equipment.

Practical Applications of Transformer Impedance Calculations

Accurate transformer impedance calculations find applications in various areas of electrical power system analysis and design.

Load Flow Analysis

In load flow studies, impedance values are crucial for determining the voltage profiles, power flows, and losses in a power system. By considering accurate transformer impedance, load flow analysis can provide valuable insights into the system's behavior under different operating conditions.

Fault Studies and Protection Coordination

During fault studies and protection coordination, transformer impedance values are utilized to determine fault currents, protective relay settings, and selectivity between protective devices. Accurate impedance calculations enable the effective coordination of protection devices and enhance system reliability.

System Stability Studies

Transformer impedance is a vital input parameter for system stability studies, including transient stability and small-signal stability analysis. By considering precise impedance values, engineers can assess the system's stability margins, identify potential stability issues, and devise corrective measures.

Transformer Impedance Formula

The impedance of a transformer is typically represented as a percentage, known as the impedance voltage, in relation to its rated voltage. The basic formula for calculating transformer impedance is:

Impedance (%) = (Impedance Voltage / Rated Voltage) * 100

For example, let's assume a transformer has an impedance voltage of 4 kV and a rated voltage of 11 kV. Plugging these values into the formula, we can calculate the percentage impedance as follows:

Percentage Impedance (%) = (4 kV / 11 kV) * 100 = 36.36%

Example 1:

Let's assume we have a transformer with an impedance voltage of 4 kV and a rated voltage of 11 kV. To calculate the percentage impedance:

Percentage Impedance (%) = (Impedance Voltage / Rated Voltage) * 100

                        = (4 kV / 11 kV) * 100

                        ≈ 36.36%

Therefore, the percentage impedance of the transformer in this example is approximately 36.36%.

Example 2:

Consider a different transformer with an impedance voltage of 1.2 kV and a rated voltage of 480 V:

Percentage Impedance (%) = (Impedance Voltage / Rated Voltage) * 100

                        = (1.2 kV / 480 V) * 100

                        = 0.25%

In this case, the percentage impedance of the transformer is 0.25%.

It's important to note that the actual percentage impedance values can vary depending on the specific transformer design, construction, and intended application. Proper consideration of factors like core material, winding configuration, conductor size, and insulation is necessary to determine accurate percentage impedance values for a given transformer.

Transformer Impedance Percentage Calculator

Impedance Voltage (V): Rated Voltage (V):

Advantages of Parallel Transformer Connection

The parallel connection of transformers offers several advantages in power systems. Some of the advantages of parallel transformer connection are:

Increased power capacity: The parallel connection of transformers increases the power capacity of the power system, allowing more power to be transmitted and distributed.

Improved reliability: The parallel connection of transformers provides redundancy in power systems, ensuring that the power supply is continuous and reliable.

Better voltage regulation: The parallel connection of transformers ensures better voltage regulation and stability in power systems.

Disadvantages of Parallel Transformer Connection

The parallel connection of transformers also has some disadvantages in power systems. Some of the disadvantages of parallel transformer connection are:

High initial cost: The parallel connection of transformers requires special transformers that are designed for parallel operation, which can be costly.

Complicated control: The load sharing in parallel transformers requires special control and protection systems, which can be complicated to implement.

Risk of unequal loading: The risk of unequal loading can occur if the transformers are not designed for parallel operation or if the load sharing system fails.

Examples of the Parallel Connection of Transformer:

1. Two 10 MVA transformers with a typical impedance of 5% are connected in parallel to provide a total power capacity of 20 MVA.
2. A substation has four 15 MVA transformers with a typical impedance of 6% connected in parallel to provide a total power capacity of 60 MVA.
3. A large industrial plant has three 20 MVA transformers with a typical impedance of 8% connected in parallel to provide redundancy and ensure a reliable power supply to critical loads.
4. A data center has multiple 30 MVA transformers with a typical impedance of 10% connected in parallel to provide a high-power capacity and ensure uninterrupted power supply to critical loads.
5. A utility substation has two 50 MVA transformers with a typical impedance of 12% connected in parallel to ensure a reliable power supply to a large commercial area.
6. In a power system, two 500 kVA transformers are connected in parallel to increase the power capacity to 1000 kVA.
7. A hospital has four 500 kVA transformers connected in parallel to ensure a continuous and reliable power supply to critical loads.
8. A manufacturing facility has three 750 kVA transformers connected in parallel to provide redundancy and ensure efficient operation of the power system.
9. A data center has multiple 1000 kVA transformers connected in parallel to provide a high-power capacity and ensure uninterrupted power supply to critical loads.
10. A residential area has two 100 kVA transformers connected in parallel to ensure a reliable power supply to homes and businesses.

Summary

The parallel connection of transformers is essential to ensure efficient and reliable power supply in power systems. The parallel connection of transformers increases the power capacity, provides redundancy, and ensures better voltage regulation. Load sharing in parallel transformers is crucial to ensure that each transformer shares an equal portion of the load. Although the parallel connection of transformers has some disadvantages, the benefits outweigh the drawbacks.

FAQs

What is the purpose of connecting transformers in parallel?

Connecting transformers in parallel increases the power capacity and provides redundancy to ensure a reliable power supply. It also enables load sharing, which helps to distribute the load evenly among the transformers.

How are transformers connected in parallel?

Transformers can be connected in parallel by connecting their primary and secondary windings in parallel. The transformers should have the same voltage rating, phase sequence, and turns ratio.

What is the typical impedance of a transformer connected in parallel?

The typical impedance of a transformer connected in parallel is usually between 2% to 15%, depending on the transformer's size and application.

What are the advantages of connecting transformers in parallel?

The advantages of connecting transformers in parallel include increased power capacity, redundancy, load sharing, and improved reliability of the power system.

Are there any limitations to connecting transformers in parallel?

Yes, there are some limitations to connecting transformers in parallel. The transformers should have the same voltage rating, phase sequence, and turns ratio. They should also have similar impedance and operate at the same frequency. Failure to meet these requirements can result in unbalanced loading, voltage regulation issues, and other problems.