Conditions for Parallel Operation of Transformers (English Version)

In power systems, to enhance the reliability of power supply, balance loads, and optimize resource utilization, it is often necessary to operate multiple transformers in parallel. However, not all situations allow direct paralleling without meeting certain technical conditions to ensure safety and stability. This article details the main conditions required for transformers to operate in parallel and their significance.

1. Basic Concept of Parallel Operation

Parallel operation of transformers refers to connecting two or more transformers' primary sides to the same power source while their secondary sides jointly supply power to the load. This mode of operation can effectively share the load, reduce pressure on individual equipment, provide redundancy, and enhance the reliability of power supply.

2. Conditions Required for Parallel Operation

To ensure the safety and stability of parallel operation, several critical conditions must be met:

1. Same Voltage Ratio
   The voltage ratio (the ratio between the primary side voltage and the secondary side voltage) of the transformers must be identical. If the voltage ratios do not match, circulating currents may occur, increasing losses and potentially damaging the equipment.

2. Identical Connection Groups
   The winding connection groups of the transformers (such as Yyn0, Dyn11, etc.) must be exactly the same. Different connection groups can lead to phase differences, resulting in significant current surges that affect grid stability.

3. Equal or Similar Short-Circuit Impedance
   Short-circuit impedance reflects the combined characteristics of internal resistance and leakage reactance within a transformer. During parallel operation, if the short-circuit impedances vary significantly among transformers, uneven load distribution may occur, leading to some transformers being overloaded while others are lightly loaded, affecting overall efficiency.

4. Appropriate Capacity Ratio
   There should be a reasonable capacity ratio among transformers operating in parallel. It is generally recommended that the capacity of a single transformer does not exceed one-third of the total capacity, ensuring balanced loads and preventing system-wide failure due to the malfunction of one transformer.

3. Advantages of Parallel Operation

• Improved Power Supply Reliability: Even if one transformer fails, the others can continue to work, ensuring continuous power supply.
• Load Balancing: Flexibly adjust the working state of each transformer based on actual load requirements, extending equipment lifespan.
• Facilitates Maintenance: Allow maintenance or replacement of some transformers without interrupting power, reducing downtime.

4. Precautions

While parallel operation offers many advantages, there are also considerations during implementation:

• Regular Inspections: Ensure all transformers meet the required technical parameters and promptly identify and resolve potential issues.
• Proper Configuration: Select appropriate combinations of transformers to avoid severe capacity imbalance.
• Monitoring System: Establish a comprehensive monitoring mechanism to monitor the operational status of transformers in real-time, enabling swift responses to abnormal conditions.