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.

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.

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.

Based on the radiation of the transient electromagnetic fields in lightning discharge channel, we establish the simulated model of lightning channel in the laboratory and analyze the data and waveform, which are received by the low frequency magnetic antenna and the plate capacitance electric field change instrument. Thus we draw some conclusions. In the experiment, the energy of lightning current is mainly concentrated in the low-frequency stage, and the difference of energy between two frequency point decreases with the frequency growth. The waveform of plate capacitance appears after that of magnetic antenna. As the impulse current increasing, the coupling amplitude and energy of the antenna have an increased trend and the growth of the magnetic antenna is more stable. When distance is further, the amplitude and energy of the antenna present a tendency of decrease. And the forepart is steep and the back is flat. The results have some significance on the research of lightning return stroke and lightning electromagnetic fields.