Deshu Chen

Online rotor mixed fault diagnosis way based on spectrum analysis of instantaneous power in squirrel cage induction motors

Broken rotor bars and eccentricity are common faults in squirrel cage induction motors. These two faults usually occur simultaneously. This paper will deal with this kind of mixed fault. It is well known that the characteristic frequency of broken bars in the stator line current of a squirrel cage induction motor is very near to that of the fundamental component. In the spectrum of the stator line current, the characteristic components related to broken rotor bars are always submerged by the fundamental one, and it is difficult to detect the broken bar fault at an early stage. In our work, instantaneous power of the motor is used as the quantity to be monitored. Theoretical analysis indicates that the spectrum of ac level of the spectrum of the instantaneous power is clear from any component at the fundamental supply frequency, and the fault characteristics can be highlighted, which is effective toward the separation of mixed faults and the quantification of the fault extent. Experimental results have demonstrated the effectiveness of the proposed technique.

A nonlinear variable structure stabilizer for power system stability

A nonlinear variable structure stabilizer is proposed in this paper. Design of this stabilizer involves the nonlinear transformation technique, the variable structure control technique and linear system theory. Performance of the proposed nonlinear variable structure controller in a single machine connected to an infinite bus power system and a multimachine system with multimode oscillations is simulated. The responses of the system with the proposed stabilizer are compared with those obtained with some other kinds of stabilizers when the system is subjected to a variety of disturbances. Simulation results show that the nonlinear variable structure stabilizer gives satisfactory dynamic performance and good robustness. >

Study of wavelet-based ultra high speed directional transmission line protection

A novel wavelet-based directional protection scheme is presented. Using the theory of wavelet singularity detection as a powerful signal processing tool, the initial arrival of the traveling wave and its sign can be identified reliably. Characteristics of the proposed directional protection algorithm are analyzed and the result of simulation studies are given. The wavelet based directional protection scheme solves several problems existing in current protective relays and is suitable for use as an ultra-high-speed UHV/EHV transmission line protective relay.

A novel technique for measuring grounding capacitance and grounding fault resistance in ineffectively grounded systems

A principle for resonance measurement based on injecting a resonant frequency signal is presented in this letter. Using this principle, the grounding capacitance of lines and equipment and the grounding fault resistance can be measured on-line in ineffectively grounded systems. Based on this, Petersen-coil automatic tuning is implemented and 100% stator grounding fault protection for generator stator windings is also proposed. The prototype for Petersen coil tuning has been tested on networks for many years. The new method for generator stator grounding fault protection is verified by simulation.

Experiment research on differential protection for UHV transformer in China

Ultra-high voltage (UHV) transmission possesses enormous economic benefits and technical superiorities, which is a new subject for China and must be studied emphatically. This paper introduces the actual configuration and parameter of UHV transmission under construction in China and its physical dynamic simulation (PDS) experiment model. According to the structure and operation characteristics of 1000 kV UHV transformer, the paper studies and proposes the differential protection scheme of UHV transformer through analyzing a great deal of PDS experiment results. The research shows that the complete differential protection of main transformer canpsilat operate sensibly and the differential protection of the voltage regulating winding and the voltage compensating winding are needed respectively, when the voltage regulating winding and the voltage compensating winding inter-turn faults happen. These differential protectionspsila operating performance of the second harmonic restraint when switching on an unloaded transformer is analyzed.

Simulation Analysis of Dynamic Performance for Hydro-Generator Under Loss of Excitation Condition

In order to analyze the dynamic performance for hydro-generator under loss of excitation (LOE) condition more effectively, based on MATALB, a mathematical model of hydro-generator under LOE condition is constructed in this paper. The model includes synchronous generator model, speed governor model, hydraulic turbine model, excitation regulation model and transmission line model. Several types of LOE faults are simulated by the model, and the simulation waveforms of related electrical quantities are compared with theoretical analysis result, thereby the feasibility of simulation model is proved

Research on sympathetic interaction between transformers

The phenomenon of sympathetic interaction between transformers is discussed in this paper. A mathematical model is developed for two transformers in parallel and in series operation to analyze the origin mechanism of sympathetic interaction. At the same time, its characteristics are further analyzed by numerical simulation. The sympathetic inrush current could influence the transformer differential protection. The physical dynamic simulation experiment results are analyzed, which prove the second harmonic restrain method could restrain the sympathetic inrush and the CT saturation criterion should be used for the differential protection.

Study on the Unusual Misoperation of Differential Protection During Transformer Energization and its Countermeasure

The differential protection of the transformer, generator, or transmission line under normal operating conditions may misoperate when the adjacent transformer is switched-on. To research the cause of the misoperations, impacting factors, such as magnetizing inrush, sympathetic inrush, and current-transformer saturation are analyzed based on the field-recorded fault data and the simulation results in this paper. It is disclosed that the CT transient or CT local transient saturation, which are caused by the long-lasting dc component from the magnetizing inrush current, will lead to misoperation. To solve this problem, a new CT saturation detection algorithm based on the dc component in secondary current is proposed to prevent this sort of misoperation, and the effectiveness of the proposed algorithm is proved by the field-recorded fault data and simulation results obtained under different conditions.

The Study of Transient Performance for Electronic Current Transformer Sensor Based on Rogowski Coil

Applying Rogowski coil in power system is very attractive because of its numerous merits. A good accuracy can be achieved when Rogowski coil is used for metering. But the response to transient fault current should be studied when Rogowski coil is used for relay. This paper analyses the transient performance of Rogowski coil with ideal integrator. The analysis shows it has excellent transient performance. But the transient performance will be degraded greatly when Rogowski coil is accompanied with improper designed practical integrator. A set of correct parameters is chosen based on simulation analysis. Experiments proved that the current sensor based on Rogowski coil has perfect transient performance

Transient Simulation Model and Its Simplified Method Validation for Huge Hydro Generator Internal Short Circuit Faults

Based on the summary of the research about internal short circuit faults and the main protection scheme for huge multi-branch hydro generator, the significance to research transient process in faulty condition is pointed out in the paper. By far, there almost have no perfect simulation model suits for generator optimized main protection scheme research based on internal fault transient process simulation. In this paper, the theory and validation of the simplified transient simulation model, which based on ldquodual damper bars on each polerdquo principle is proposed and explained. The simplified transient simulation model can satisfy the demands for engineering application both on calculation precision and on solving speed, so its merit for engineering practicality is demonstrated, and it provides a new approach for optimized main protection scheme research for huge hydro generator.