What are the special designs and requirements for the application of generators in wind farms and hydropower stations?

1、 Generator in wind farm

Variable speed constant frequency design

In wind power generation, the wind speed is constantly changing. In order to ensure the stable output frequency of the generator, variable speed constant frequency technology is usually used. This requires the generator to be able to adapt to a wide speed range, such as a doubly fed induction generator. Its rotor winding is connected to the power grid through a frequency converter. When the wind speed changes and the wind turbine speed changes, the frequency converter can adjust the frequency of the rotor current, thereby keeping the stator output frequency constant to meet the strict requirements of the power grid for electrical energy frequency.

Taking a certain offshore wind power plant as an example, the wind speed may vary between 3-25m/s. The doubly fed induction generator can effectively convert the mechanical energy of the wind turbine into electrical energy at different wind speeds, with a variable speed range of about ± 30%, ensuring a stable output frequency of 50Hz (or 60Hz).

Low wind speed start-up and high wind speed protection design

The generator needs to have the ability to start at low wind speeds. Generally speaking, when the wind speed reaches the cut in wind speed (usually around 3-4m/s), the generator should be able to start smoothly. This requires the generator to have a small starting torque and the control system to accurately detect the appropriate starting wind speed.

At the same time, in order to prevent damage to the generator and blades at high wind speeds (usually around 20-25m/s), the generator needs to work in conjunction with protective devices such as pitch control systems. When the wind speed exceeds the cut-out wind speed, the pitch angle of the blades will be adjusted to reduce the wind energy capture of the wind turbine. At the same time, the generator can stop running through braking devices and other means to protect equipment safety.

Anti fatigue design

Due to the intermittency and volatility of wind, the components of wind turbines are subjected to frequent alternating loads. The key components of the generator, such as the shaft and bearings, need to be made of anti fatigue materials, and the structural design should consider reducing stress concentration. For example, the shaft of a generator is usually made of high-strength alloy steel, and its shape is designed to avoid sharp corners as much as possible to prevent cracking under long-term alternating stress.

2、 Generator in hydroelectric power station

Adaptive design for high and low water head

In hydroelectric power plants with high water head (large drop), if the water head exceeds several hundred meters, impulse generators are usually used. It uses high-speed water flow to impact the impeller of the water turbine, causing the impeller to rotate and drive the generator to generate electricity. This type of generator has a high rotational speed and requires a good sealing and lubrication system to adapt to the working environment at high speeds.

For low head (small drop) situations, such as some riverbed hydropower stations, axial flow or through flow generators are generally used. The wheel shape of an axial flow generator is suitable for efficiently utilizing water flow energy at low water heads, and the blade angle can be adjusted according to the water flow rate. The through flow generator is a horizontal axial flow generator with a compact structure, suitable for low head and high flow hydraulic resources.

Waterproof and moisture-proof design

The generators of hydroelectric power plants usually operate in humid environments and face the risk of water erosion. Therefore, the casing of the generator needs to have good waterproof and moisture-proof performance. For example, the stator and rotor windings of a generator require special insulation materials, and the surface of the windings will be coated with moisture-proof paint. At the same time, the sealing structure of the generator should be tight to prevent moisture from entering the interior of the motor and causing faults such as short circuits.

Large capacity and high stability design

Many large hydroelectric power stations have enormous installed capacity, such as the Three Gorges Dam, which has a single unit capacity of up to 700000 kilowatts. This requires the generator to have a large capacity for power generation and play an important role in stabilizing frequency and voltage in the power grid. The magnetic field system and winding design of the generator should be able to withstand high currents and voltages, and be able to quickly adjust when the load changes, maintaining the quality of the output electrical energy. For example, large hydroelectric generators use vertical semi umbrella or suspended structures, which can better withstand huge electromagnetic and mechanical forces and ensure the stable operation of the generator.