Hongzhong Ma

The survey of electrical control systems of wind turbine generators

This paper summarizes electrical control systems of wind turbine generators. Based on the classification of fixed speed generator and variable speed generator, permanentmagnet synchronous generator (PMSG) and doubly-fed induction generator (DFIG) are introduced basically. In the blade pitch angle control systems, hydraulic and electric pitch angle control systems are introduced comparatively. In the aspect of intelligent control technology, fuzzy control and neural network control are introduced principally on their characteristics and applications.

Feasibility research on DC generator based wind power generation system

The biggest difference between wind turbine generating units and other traditional ones (hydro and thermal generating sets) is its frequent variation of the prime mover output power and difficulties in control, due to the volatility and the uncontrollability of wind speed. In consideration of the characteristics of wind power system and Direct Current (DC) generator, a wind power generation system based on DC generator is developed, and the feasibility and advantages of this system are analyzed theoretically, with emphasis placed on its control strategy. Then, a simulative system of wind power generation system based on DC generator is built in the power system dynamic simulative laboratory. At last the feasibility and advantages of the system are verified by elaborate experiments. Both theoretical analysis and the studies prove the excellent regulating characteristics on the voltage fluctuation caused by the frequently variable wind speed and load changes for the system which working with the variable pitch parts to satisfy the requirement of the dynamo in the wind power system.

Partial discharge diagnosis by simultaneous observation of discharge pulses and vibration signal

Protrusion defects on inner conductor can seriously weaken the dielectric strength of gas insulated switchgear (GIS). In practice, pulse current method (IEC 60270) and vibration method sometimes are ineffective for this type of defect. Clarification of coincidence of partial discharge (PD) characteristics measured with both methods is very important for further application of the vibration method. In this paper, PD pulses and vibration signal recorded on enclosure generated from artificial protrusions mounted on inner conductor with different lengths and diameters were measured synchronously by using a 252 kV GIS PD test system. The test GIS was filled with the gas SF6 of the standard atmosphere pressure (i.e. 101 kPa), and the power frequency of the test voltage was 50 Hz. The pulse repetition frequency (PRF) characteristics and frequency-resolved vibration (FRV) characteristics under different discharge level were investigated. The dynamic response (DR) characteristics of the experimental GIS are also obtained by using the force hammer test. For a good understanding of PD vibration characteristics, the relationship between FRV, PRF and DR was analyzed in detail. To make more reliable operations of GIS, an improvement vibration method for protrusion defect detection was developed and applied.

Finite element analysis of large transformer winding looseness

In order to study the relationship between the pre-compression force and the winding looseness of large transformer, the influence of different preload on the vibration signals of transformer is analyzed by the finite element. The model of transformer winding is introduced into ANSYS Workbench so that the modal analysis and the harmonic response analysis can be carried out. It can be found that the displacement under small pre-compression forces in the range of natural frequencies is more obvious than that under large pre-compression forces and the middle of winding is easy to loosen and deform. Furthermore, the natural frequency shifts to the low frequencies with the decrease of the pre-compression force of the winding. Therefore, the response characteristics of transformer under different pre-compression force can be calculated to research the winding looseness of large transformer.

Novel method for partial discharge detection in gas insulated substation

For the insulation diagnosis of electrical imaterials in power apparatus, partial discharge (PD) measurement has been recognized as an important tool. In this paper, electrical and mechanical methods were combined for the detection of the PD defect. To analyze the fundamental frequency vibration, the induced current including eddy current and circulating current in GIS was analyzed firstly. Then, PD pulses and vibrations on enclosure were measured on a 252kV GIS PD test system. PD faults included protrusion and insulator flashover. The phase of the pulse current of the two kinds of PD defects was analyzed. Meanwhile, the frequency spectrum of vibration on the GIS equipment was analyzed. In order to diagnose the partial discharge fault better, the relationship between the pulse current signals with the vibration signal was established. A more reliable PD detection method was proposed by combining with the electrical signal and the vibration signal.