Safety system in wind turbines

1. The status of safety system in the operation of wind turbines

Safety production is a basic principle in the management of wind farms in China. Wind farms are mainly composed of wind turbines, so the operational safety of wind turbines is the most important for wind farms. The control system is the core component of the wind turbine and is the fundamental guarantee for the safe operation of the wind turbine. Therefore, in order to improve the operational safety of the wind turbine, it must start from the safety and reliability design of the control system, according to the wind turbine control system. The characteristics of different links such as power generation, transmission and operation control, in the whole process of equipment installation and operation, we must effectively improve the safety and quality, and constantly seek ways and methods to improve the safety and reliability of wind turbines.

The safe production of wind turbines is a safety system engineering, and the control system is an important part of the wind turbine. Its safety system forms part of the whole safety system. It needs to be based on system theory, information theory and cybernetics. Production management of equipment, research on accidents, and prevention of accidents. From the system point of view, the longitudinal analysis from design, manufacture, installation, testing, operation, maintenance, comprehensive analysis, horizontally from component purchase, process, procedures, standards, organization and management, and finally comprehensive comprehensive evaluation. The purpose is to minimize the unsafe factors of the wind power generation system and achieve the best safety state production.

2. Unit control operation safety protection system

(1). The wind protection safety system is designed with the cut-in wind speed Vg and the stop wind speed Vt. Generally, the wind speed of 25m/s for 10 minutes is the stop wind speed; since the wind energy is very large, the system must take protective measures before the shutdown. For stall fans, wind turbine blades automatically reduce the capture of wind energy. The power output of the wind turbine group is still maintained at the rated power. For the variable pitch fan, the blade pitch angle must be adjusted to achieve power output regulation and limit the maximum power. The output ensures the safe operation of the generator. When the wind is shut down, the crew must stop in accordance with the safety procedures. After shutdown, the wind turbine set must be controlled by 90° wind.

(2). The parameter exceeds the limit. In the operation of the wind turbine group, there are many parameters to be monitored. For the different units to operate, the specified limit value is different. The temperature parameter is calculated by the computer sample value and the actual working condition to determine the upper and lower limits. The limit of the pressure parameter, using the pressure relay, according to the working conditions, determine and adjust the limit set value, the relay input contact switch signal to the computer system, the control system automatically distinguishes the processing. The voltage and current parameters are converted into a computer control system by the power sensor, and the parameters of the over-current and voltage control are determined according to the working conditions and safety technical requirements.

(3). Voltage protection refers to the protection of the instantaneous high-voltage impact on the components of the electrical equipment. Generally, the AC power supply of the control system is isolated and stabilized. At the same time, the device is equipped with high-voltage transient absorption components to improve the high-voltage capability of the control system. .

(4). Current protection control system All electrical circuits (except the safety chain) must be equipped with overcurrent protectors, such as fuses and air switches.

(5). The vibration protection unit is equipped with three-stage vibration frequency protection, vibrating ball switch, vibration frequency upper limit 1, and vibration frequency limit 2. When the switch is activated, the system will process it hierarchically.

(6). Start-up protection design unit start normal sequence control, for fixed-pitch stall asynchronous wind turbines adopt soft-cut control to limit the electric shock to the grid when grid-connected; for synchronous wind turbines, take synchronous, in-phase, same-pressure Net control, limiting the current impact when connected to the grid.

(7). Shutdown protection The wind turbine group needs to be safely shut down in the case of small winds, strong winds and faults. The sequence of shutdown should be air pneumatically braked first, then softly cut off the grid and shut down. The sequence control of the soft off-network is basically the same as the control of the soft grid.

(8). Emergency stop safety chain protection Emergency stop is an effective barrier for the safety protection of the unit. When the vibration switch operates, the speed exceeds the speed, the power grid is interrupted, the unit components are suddenly damaged or the fire occurs, the wind turbine group is shut down urgently, and the system safety chain The action will effectively protect the working conditions of all aspects of the system, and the control system will stop the unit smoothly in about 3 seconds.

3. Electrical grounding protection system

(1). Basic concept of grounding

A. Grounding device

A good electrical connection between any part of the electrical equipment and the soil becomes grounded, and the metal body in direct contact with the soil is called a grounding body. The metal wire connecting the grounding body to the electrical equipment is called the grounding wire. The grounding and the grounding body are called grounding devices. Grounding Under normal conditions or accidents, in order to ensure the safe operation of electrical equipment, the electric control system must be grounded at one point. For example, grounding the center point of the transformer is called working ground.

B. Protective grounding

In order to prevent the risk of electric shock due to insulation damage, the metal casing of the uncharged electrical equipment is connected with the grounding device, and the control board and the motor casing are grounded, which is called protective grounding.

C. The role of grounding

The role of protective grounding Once the insulation of electrical equipment is broken, it can be seen that the voltage of the outer casing is limited to the safe voltage to prevent personal electric shock.

The function of protecting the zero connection Once the insulation of the electrical equipment is broken, a short circuit with a small impedance is formed, which generates a large short-circuit current, which causes the melt to cut off the faulty circuit within the allowable time to avoid an electric shock accident.

The role of working grounding reduces the contact voltage of the human body, quickly cuts off faulty equipment, and reduces the insulation level of electrical equipment and power line design.

D. Repeated grounding

In the neutral point grounding system of the wind field, the low-voltage line where the neutral point is directly grounded, the neutral line at the tower (neutral point) should be repeatedly grounded; the low-voltage cable without the special neutral line or the metal sheath as the neutral line should be grounded repeatedly. Cables and overhead lines are introduced into the building. If the grounding point exceeds 50M, the neutral line should be grounded. When metal pipe wiring is used, the metal pipe should be connected to the neutral wire and then grounded repeatedly. When wiring with plastic pipe The steel wire with the interface of not less than 10mm2 should be laid outside the pipe and connected to the neutral wire and then grounded repeatedly.

Each repeated grounding resistance does not exceed 10Ω, and for power supply (transformer) capacity below 100kVA, each repeated grounding resistance does not exceed 30Ω, but at least three places must be repeatedly grounded.

(2), unit grounding protection device

A. The grounding body is divided into an artificial grounding body and a natural grounding body. The grounding device should make full use of the natural grounding that is connected to the earth, that is, the body tower and the foundation. However, for reliable grounding, the artificial grounding body can be designed to connect with the tower and the foundation to form a grounding net, which has better lightning protection and The impact of high current and large voltage, and the grounding design device of the winding ring and the grounding rod must be installed, that is, the grounding protection device.

B. The artificial grounding body should not be buried in garbage, slag and strongly corrosive soil. When buried, the depth of the grounding body should be no less than 0.6m, the length of the vertical grounding body should be no less than 2.5m, and the new soil should be used around the embedding.

C. The grounding body connection should be lap welding, the lap length is twice the length of the flat steel, and it is welded by three adjacent sides, which is six times the diameter of the steel, and is welded by both sides. The grounding body is connected to the grounding wire and should be connected with a detachable bolt to test the resistance.