Corona plays an important role in both initiation and development process of leaders around wind turbine blades. In this paper, based on laboratory experiments and numerical simulation, the corona triggering tests are performed by analyzing corona discharge characteristics of wind turbine blades. The corona threshold voltage and the corona current are measured. The corona environmental threshold and the corona triggering threshold are evaluated and discussed in detail. The influence of blade lengths, rotational angles and rotational speeds is analyzed. The results show that the corona trigger threshold obtained is a constant and is about 321.29 kV/m, which appears to be some fluctuations due to atmospheric conditions and charged ions. In addition, through analysis the corona triggering threshold of different rotational angles and the corona environmental threshold of different rotational speeds, rotational wind turbine blades affect the electric field near the blades by varying the blade height and the charged ions distribution at the tip of the blades where the altered blade height accounts for the dominant factor. The above research results are valuable for the understanding of the initiation and development of leaders around the wind turbine blades.

For the problem of twisted pair coupling lightning electromagnetic impulse, using a combination of test and theory, established a experimental model of twisted pair coupled lightning electromagnetic impulse, get the twisted pair coupling lightning electromagnetic impulse voltage and spectrum characteristics, test results: (1) The situation of twisted pair link matching resistance (100 [Formula: see text]): the coupling voltage increases with the addition of the impulse current; Meanwhile, there is not much impact when increase the height of the coupling voltage. (2) The situation of twisted pair link ground electric resistance: the coupling voltage was positively correlated with the ground electric resistance value in the same height; The coupling voltage increases with increasing height when the resistance value remains the same. (3) Spectral characteristics of the coupling voltage: The frequencies are mainly concentrated around the two frequencies of 8 kHz and 2.3 MHz and the magnitude of the coupling voltage is proportional to the ground electric resistance and the impulse current. The experimental results are in good agreement with the theoretical analysis. The results have some guiding significance.

In order to study the problem of damage that caused by lightning overvoltage to the transistor, we designed the experiments of combined wave impact on the transistor under different conditions by analyzing the theory of the secondary breakdown of the transistor caused by the lightning electromagnetic pulse. These cases are carried out under the condition of no protection, transient protection diode (TVS) parallel protection, and TVS tube parallel protection in the actual base amplifier circuit. It is concluded that transistor can cause it to further deteriorate under the condition of lightning overvoltage impact, and the situation of the damage can be divided into two categories, transient suppression diode in parallel with a transistor that is struck by a lightning voltage can effectively protect the transistor, which can obviously improve the resistance of the transistor. In practical amplifying circuit, applied voltage reduces the tolerance level of transistors, however, the tolerance level of transistors with transient suppression diodes in parallel is still better than the tolerance level without protection, which confirmed the conjecture that transient suppression diodes can be applied to actual circuits to protect transistors in parallel. In this paper, the theoretical analysis and experimental research on the damage of the lightning voltage on the transistor, the tolerance level of the transistor to the lightning voltage and the protection effect of the TVS tube on the transistor are carried out, which has certain reference value in the actual lightning protection of the transistor.

Lightning overvoltage may affect the signal transmission and damage terminal equipment. In order to solve this problem, the signal system Surge Protection Devices (SPDs) is designed by analyzing the signal transmission characteristic and the design theory of SPDs. The impulse tests are performed on the SPDs using a combined wave generator. Residual voltages and sharing currents are measured and discussed by considering impulse voltages, DC breakdown voltages of downstream SPDs and decoupling resistances. The blind zone of the signal system SPDs is also discussed in detail. In addition, the SPDs are equivalent to a two-port network, and the influence of distributed capacitance of the SPDs on signal transmission is analyzed for the first time through experiments. Cut-off frequency is measured and discussed by considering DC breakdown voltages of downstream SPDs and decoupling resistances. From the two experiments, the results indicate that increasing the decoupling resistance can decrease residual voltage and sharing current, but will reduce the cut-off frequency. Decreasing the DC voltage of downstream SPDs will have a similar effect. So the decoupling resistance and the DC breakdown voltage of downstream SPDs resistance need to be considered carefully in designing signal system SPDs. The sufficient research of signal system SPDs in this paper has a certain reference value in lightning protection.

Based on the invalidation and damage of the field effect transistors under lightning radiation, we establish the breakdown experiment with open-circuit voltage wave and the protection experiment with TVS as the protection device. The junction field effect transistor and the metal oxide semiconductor field effect transistor are used as material. We draw some conclusions. In the breakdown experiment, the breakdown voltage of the MOSFETs is higher than that of the JFETs as a whole. The MOSFET can be adopted in the amplifier circuit which is expected to get higher input resistance and breakdown voltage. The drain-source resistance can recover to the original resistance value after being placed a period of time, but the gate-source resistance is irreversible. The invalidation of the device under test is due to the breakdown of gate-source. The TVS can protect the FTEs well. The change of pin resistance of the MOSFET is inconspicuous. MOSFETs are more stable for debugging and development of the amplifier circuit. The results provide some significance for the development and improvement of the lightning electric fields change measuring instruments in the future.