Understanding the Wiring inside Power Plant Generators
The intricate design and functionality of power plant generators rely heavily on various electrical components, with the wiring being a crucial aspect. This article delves into the specifics of the wiring used within these generators, focusing on the sizes of wires and buss bars involved in their operation.
Introduction to Generator Wiring
Power plant generators convert mechanical energy into electrical energy. The outgoing medium voltage (from 18 to 20kV) is typically transmitted through iso-phase buses, which are large aluminum tube buses insulated and running inside protective outer tubes. These buses then connect to the low voltage side of a GSU transformer, which steps up the voltage to high voltage levels for distribution in the switchyard.
Key Components and Their Sizes
ISO-Phase Buses
The iso-phase buses are a critical part of the power generation system. They are designed to handle high currents and are reinforced by being run inside protective outer tubes. The current flowing within these outer tubes is the same as the inner conductor current, ensuring a balanced magnetic flux. This setup necessitates heavy bonding and grounding at every joint within the system to maintain safety and efficiency.
DC Excitation Wires
The direct current (DC) excitation to the rotor slip rings is another important component. For large generators, this excitation is often provided by insulated copper wires. The size of these wires can be substantial, with some polarity leads needing up to 2,150 kcmil of copper. This significant size ensures that the current demands of the generator are met without overheating or insufficiencies.
Generator Buss Bars
Contrary to the assumption that the conductors are mere wires, the buss bars within generators are substantial pieces of copper. These buss bars are typically larger in size, often approximately 2 inches by 4 inches. To accommodate the extremely high current flow, they are designed with a honeycomb hollow structure, permitting the flow of cooling water through the bars. This cooling mechanism is essential to prevent the buss bars from overheating and melting due to the intense electrical currents.
Additionally, the cooling water must be of very high purity, ensuring it remains an insulator. This high efficiency in cooling is a hallmark of good generator design, contributing significantly to the overall reliability and safety of the power generation process.
Design Considerations for Generator Wiring
The choice of wire size and buss bar dimensions is not arbitrary but is carefully determined by the generator's design and power output. For instance, a generator with a maximum output of 20,000 volts may require a minimum wire size to ensure safe and efficient operation. A generator with a full load current of 14,000 amperes, such as a 500 MW unit, would necessitate conductors of at least 14,000 sqmm or larger, depending on other design features including the cooling system and the temperature rating of the insulation.
Conclusion
Understanding the intricacies of generator wiring is crucial for optimizing the performance and reliability of power generation systems. From the iso-phase buses to the substantial buss bars and the efficient cooling systems, each component plays a vital role. By carefully selecting the appropriate wiring and buss bar sizes, engineers can ensure that power plants operate at their highest efficiency, providing reliable and secure power to millions of households and industries worldwide.