一种基于环形间隙放电器的新型风力发电机组防雷系统

The surge current flow inside the tower may create a large inductive current in low-voltage circuits such as control, measurement and communication devices. Thus, the conventional grounding system is potentially weak for the protection of low-voltage circuits inside the wind turbine. By contrast, the proposed system has two ring-shaped electrodes of several meters diameter, one of which is vertically attached to the nose cone and the other laterally placed on top of the wind tower lying just below the nacelle.
   The pair of rings is arranged with a narrow gap of no more than 1 m to avoid mechanical friction during rotation of the blades and the nacelle’s circling. When lightning (here, suppose the current is positive)strikes a blade, the lightning current reaches the upper ring from a receptor through a conductive wire installed on the blade.
    Then, the electric field between the two rings becomes high and finally sparks over and the lightning current flows downwards. The current propagates along the lower ring and grounding wire,which is arranged outside the wind tower rather than inside, and is safely led to a grounding electrode sited far enough away from the grounding for the tower.

    2.新型雷电防护系统的提出
    图1 是常规机组防雷接地系统与概念性防雷系统的说明。通常雷电流是从叶片接闪器通过叶片内部的导雷电缆到达变浆轴承，并且通过变浆轴承向轮毂、主轴在经过偏航轴承通过电缆传导至接地网。强大的雷电流在塔筒内会产生巨大的雷电电磁脉冲，如果接地线靠近动力和低压控制电缆，则会产生巨大的影响。
    因此，常规的接地系统可能加剧雷电对机组低压控制系统的影响。相反，这种系统利用安装在轮毂上的环形电极，并且与叶片内部的电缆连接形成导雷通道；另一个环形电极安装在靠近机舱底部的塔筒上，两个环形电极分别处于不同的水平轴和垂直轴上，两个电极间保持一个不到1m的放电间间隙，保持这个间隙的目的在于避免有轮毂和塔筒发生偏转时可能造成的摩擦以及防止环形电极碰撞造成损坏而影响机舱偏航。当有较大雷电流通过叶片到达环形电极时，由于间隙间存在较高的电场形成两个电极间的触发，使雷电流通过两个环形电极进行放电，这个放电的过程会形成可见的电流通道，由于电流时通过塔筒的外表面而不是内部的导线，所以也会减小雷电电磁脉冲的强度，雷电流会通过塔筒直接入地。
    3. Downsized Model of Wind Turbine
    To verify the effectiveness of the proposed lightning protection system, the author conducted a trial test using a 1/100 downsized model that on a 1/100 scale accurately simulated an actual 2 MWwind turbine with a hub height of 60 m and a blade radius of 39 m (therefore, the hub height of the model is 60 cm and the blade radius 39 cm, as shown in Figs 2 and 3). The blades of the model are made from nonflammable ABS resin and the nacelle and  tower from PC iron.
    The ring-shaped electrodes of the model are of 4 mm φ copper wires, and the diameter of the upper and lower electrodes are 5.4 and 7.7 cm, respectively. On the surface of the blades, 2 mm φenamel wires are strained to simulate receptors and down conductors. Also, as the outer down conductor, 2 mm φenamel wires drop down from the backside of the lower ring to the ground plate which is 20 cm distant from the base of the wind tower. The gap between two rings, g,and the distance between the upper ring and the nacelle,d, are design variables in the model. A detailed structure is shown in Fig. 4 in a CAD drawing and a photo of a prototype. Simulated lightning impulses with a wavefront of 1.3 μs, wavetail 49 μs, altitude 664 kV were generated using a 800 kV and 5 kJ impulse generator, as shown as Fig. 5.

　　3. 按比例缩小的试验用风机模型
　　为了验证这种防雷系统的有效性，作者做了一个试验性的测试。用1:100的比例模型，精准的建立一个机组高度为60m，叶轮半径为39m的风力发电机组模型（模型的机舱高度为60cm,叶轮半径为39cm，如图2、3所示），模型叶片采用阻燃的ABS树脂材料制成，机舱和塔筒采用铁皮制作。两个电极采用4mm的铜线制作，轮毂和塔筒上的环形电极直径分别为5.4cm和7.7cm。在叶片表面采用2mm的搪瓷线模拟叶片接闪器和引下线（导雷电缆），同样，塔筒上的环形电极采用搪瓷线连接到接地板上，长度约20cm，两个电极间的距离经过精确地计算，保证间隙不会阻碍叶轮的旋转。通过CAD制图工具制作出如图4所示的实际结构，采用800kV和5Kj脉冲发生器模拟雷电流脉冲，采用1.3/49μs冲击波形，脉冲电压为664 Kv,如图5所示。

　　4. Impulse Test in a Downsized Model