In the context of substation power supply and output, it's essential to analyze the safety type, quantity, and capacity of transformers, as well as their economic operation conditions. By combining real-world operational examples, this article introduces the selection of transformer capacity and number, emphasizing the balance between safety and economic benefits. It also outlines key precautions to ensure reliable power supply and efficient operation.
1. **Introduction**
To meet the demands of social power consumption and ensure the safety and reliability of power supply, selecting the appropriate transformer capacity and number is crucial during substation construction, expansion, or capacity increase. Choosing a capacity that’s too large leads to unnecessary investment and maintenance costs, while a capacity that’s too small may result in overloading and equipment damage. Similarly, having too few transformers can reduce power supply reliability, while too many increase costs and complicate layout and maintenance. Proper selection not only reduces initial investment but also supports safe and economical transformer operation, lowering long-term operational costs. This paper combines regulations and field experience to outline principles for transformer capacity and number selection, analyzing factors such as load demand, technical performance, and economic efficiency.
2. **Principles of Transformer Capacity and Number Selection**
Transformer capacity and number significantly influence grid structure, power supply reliability, and economy. The choice depends on current load status, growth rate, one-time investment, upper-level grid capability, and technical performance. With advancements in transformer manufacturing, efficiency has improved, and energy-saving policies encourage economic operation. However, there are still no clear guidelines in China regarding the number and capacity of transformers for new or expanded substations.
- The rated capacity should meet the total calculated load of the area, avoiding long-term overload. New substation transformers should support 5–10 years of planned load, preventing frequent expansions.
- For critical users, at least one transformer must remain operational during faults or maintenance, ensuring primary and secondary loads are met. General substations should maintain 70–80% of power supply if one transformer is out.
- In high-load areas, large-capacity transformers can reduce investment, but flexibility requires multiple units. A single transformer should not be too large or too small, allowing room for future expansion.
- To simplify operations and maintenance, transformer types should be minimized, ideally not exceeding two per substation.
- Within a certain range, increasing capacity may lower losses, but higher investment and switch requirements must be considered. Economic operation should align with national energy-saving policies.
- Urban power supply must meet N-1 reliability standards. If one transformer fails, others must handle part of the load without affecting all users.
- In densely populated areas, mutual supply between substations allows for reduced transformer capacity. However, layout and number of transformers must eventually meet load requirements.
- Substations with generator sets connected to the low-voltage side can reduce transformer capacity, but it must still meet generator output, maximum load, and backup requirements.
3. **Conditions and Requirements for Economic Operation**
Economic operation of transformers ensures safe and reliable power supply while minimizing losses and improving power factor. Factors like load distribution, parallel operation, and temperature control play a key role. Transformers must be selected based on overall reliability, technical parameters, and system compatibility.
- When building new substations in phases, the first-phase transformer should be sized for the final load, aiming for an optimal load ratio below 75%.
- Parallel-operating transformers must have matching voltage ratios, impedance, and phase relationships to avoid circulating currents and overheating.
- Transformer selection should prioritize low no-load loss, meeting national standards for efficiency and safety.
- Operating temperatures must stay within limits to prevent insulation aging and excessive losses.
- Standby transformers should be integrated into the system with automatic switching to maintain continuous power supply.
- The average load factor in the economic operating zone should be between 0.75 and 1.33, depending on no-load and load losses.
- Safe and reliable power supply is the foundation of economic operation, requiring automatic backup systems.
- Proper parallel operation and switch capacity calculations are essential to avoid system damage during faults.
This comprehensive approach ensures that transformer selection and operation contribute to both economic efficiency and long-term reliability in power systems.
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