Xianggen Yin

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.

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.

Wide-Area Backup Protection Algorithm Based on Fault Component Voltage Distribution

A new wide-area backup protection algorithm based on the fault component voltage distribution is proposed in this paper. It is helpful to overcome the problems of complex setting and maloperation under flow transfer of conventional backup protection. The measured values of fault component voltage and current at one terminal of the transmission line are applied to estimate the fault component voltage at the other terminal. Then, the fault element can be identified by the ratio between the measured values and the estimated values. In addition, the speed of fault element identification can be accelerated by a faulted area detection scheme. The proposed method has the advantage of easy setting and low requirement for synchronized wide-area data. The studies performed on the IEEE 39-bus system validate the proposed algorithm under various faults and flow transfer.

Adaptive ground fault protection schemes for turbogenerator based on third harmonic voltages

Equivalent circuits based on the actual connection of coil-groups of generators are used to study the characteristics of various generator stator ground fault protection schemes presented in the literature. The evaluation and the comparison of the characteristics of those schemes are given by means of protection coverage-critical resistance curves. Although these schemes are successful in practice, they suffer the disadvantage of low sensitivity, which is strongly related to generator operating conditions. To overcome this disadvantage, two adaptive stator ground fault protection schemes based on digital techniques are developed. Compared to conventional third-harmonic voltage schemes, they can automatically track the change of generator operating conditions before a ground fault occurs. Test results from a digital simulation show that they can keep high sensitivity during all operating conditions. >

Study of Fault Current Characteristics of the DFIG Considering Dynamic Response of the RSC

During nonsevere fault conditions, the crowbar protection is not activated and the rotor windings of a doubly fed induction generator (DFIG) are still excited by the ac/dc/ac converter. In these cases, the dynamic response of a rotor-side converter (RSC) has a large influence on the fault current characteristics of the DFIG. In this paper, an analysis method for the fault current characteristics of the DFIG under nonsevere fault conditions is proposed. First, the dynamic response of the RSC is analyzed on condition that the external power control loop is shut down and the reference signals of the inner rotor current control loop are kept constant. Then, the simplified calculation models of the rotor fault current are established according to different design principles of the inner rotor current controller. Based on it, the fault characteristics of the stator current are studied and the analytical expressions of the stator fault current are obtained. Finally, digital simulation results validate the analytical results. The proposed analysis method is applicable for the study of fault current characteristics of DFIG with different control strategies for low-voltage ride through. The research results are helpful to the construction of adequate relaying protection for the power grid with penetration of DFIGs.

Instantaneous Value and Equal Transfer Processes-Based Current Differential Protection for Long Transmission Lines

According to the theory of equal transfer process of transmission lines (ETPTL), the voltages along the line and the current through the line transformed by the same linear transferring link still satisfy the original distributed parameter-based transmission-line model. It is proved that the voltage signals near power frequency along the line follow the law of linear distribution. On the basis of the aforementioned analytical results, an ETPTL-based new current differential protection scheme for long transmission lines by using restructured instantaneous value was presented. The primary voltage and current experience equal transfer processes and are transformed to be virtual instantaneous values before they are used by differential protection. According to the instantaneous voltage value of the transmission line, the instantaneous values of the capacitive current can be calculated. After removing this current, the instantaneous value-based differential criterion can be implemented. The results of Alternate Transients Program simulation test results show that the proposed technique has highly reliability, fast speed, excellent performance under high-resistance earth-fault conditions, and phase selection ability.

Wide-Area Protection Fault Identification Algorithm Based on Multi-Information Fusion

Wide-area protection systems can be used to avoid complicated setting coordination of traditional backup relays and effectively prevent cascading trip events. Since they depend on a multisource data of transmission network to identify a faulted element, fault-tolerance capacity of the system is required. This paper proposes a faulted element identification algorithm based on multisource information fusion for wide-area protection. A fault identification encoding method based upon grid topology is presented. Meanwhile, the operation information of traditional primary/backup relays and the status of breakers are utilized to establish fitness function and state expectation function. The fitness of protected elements is used to determine their fault probability; and faulted elements are identified with high fault tolerance. The property of the presented algorithm is validated by simulation tests based on an IEEE 10-generator 39-bus system.

Review on blackout process in China Southern area main power grid in 2008 snow disaster

In the beginning of 2008, southern China had experienced extreme low temperature, heavy rain, snow, and freezing weather. This extreme weather had impaired the southern area power grid greatly and threatened the security and stability running of power system and power supply. The paper introduces the China southern area power grid basic disaster situation. Based on the China southern area power grid characters and the disastrous weather characters, it reviews the whole accident process of the 500kV main power grid in the snow disaster. Then summarizes the typical characteristics in the disaster of China southern area 500kV main power grid, and reveals the main problems exposed in the southern area 500 kV main power grid. The problems include: long distance large capacity transmission line proportion, the power supply development is not harmonious with the power grid development, and the 500kV transmission line corridor selection problem, etc. Some solutions and recommendations in power supply development and power grid development are given out according to the problems in the end.

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.

A Novel Compensation Technology of Static Synchronous Compensator Integrated With Distribution Transformer

This paper presents a novel compensation technology of static synchronous compensator integrated with distribution transformer (DT-STATCOM). STATCOM is connected with the transformer taps at the high-voltage (HV) windings. By selecting the appropriate tap voltage level, it can help to make full use of the spare capacity of the distribution transformer, simplify the main circuit topology of STATCOM, and reduce the current level of power devices. The theoretical basis for DT-STATCOM reactive power compensation is explained. For the Dyn-type transformer, the structure of DT-STATCOM with multigroup taps at the transformer HV windings is mainly designed, and its influence on the current distribution in the transformer windings is analyzed. Besides, according to the characteristics of DT-STATCOM, this paper also proposes a reactive command current calculating method based on the principle of power balance, and adopts a hysteresis current control method with a variable hysteresis band. Simulation and experimental results verify the correctness of the proposed DT-STATCOM structure and its control method.