Yuan Yubo

Analysis and countermeasure on abnormal operation of one 110kV intelligent substation merging unit

With the increase of voltage level and more and more secondary devices are located in field, the secondary circuit of substation is in a strong electromagnetic environment. Because the secondary circuit is affected by the interference of switch operations, there are many trip accidents happened in substations without any fault in recently years, which constitutes a serious threat to the power network and harms the safe operation of the electric power system. It is of great theoretical significance and practical value to study the Electro Magnetic Compatibility problem of the transformer substations substation secondary circuit. In this paper, the abnormal phenomenon of one 110kV intelligent substation merging unit is described. And the reason of the abnormal phenomenon is analyzed. Firstly, the EMC experiments specified by the IEC61000-4 standard are carried out. Furthermore, to verify the anti-interference performance of the merging unit, the Electro Magnetic Compatibility experiments above the standard are carried out. The structure of merging unit is improved until the merging unit operates normally. Secondly, to quantitatively analyze the disturbance strength, the electromagnetic disturbance signal is recorded, and the characteristics of amplitude and time-frequency of the recorded signal are analyzed. Finally, this paper puts forward some suggestions about improving the Electro Magnetic Compatibility performance of merging unit.

Short-circuit characteristics and impact of PV inverter on the protection of distribution grid

Nowadays, Photovoltaic (PV) generation is widely accepted as an alternative energy. PV unit interfaced to distribution grid effects protection action when short-circuit fault happened. In this paper, electromagnetic transient characteristics of the PV inverter short-circuit were studied by theoretical analysis and experimental verify.

Experimental analysis of EMC immunity for field installed intelligent equipment, of intelligent substation

With the construction of intelligent substation, it is a trend that the secondary intelligent devices are field installed. After field installation of intelligent devices, the electromagnetic environment in switch yard is much more serious than which in relay protection room. After the abnormal condition of the 100kV intelligent substation occurred, the EMC experiments are carried out and the structure of merging unit is improved. For quantitatively analyzing the strength of the disturbance signal, the electromagnetic disturbance signals are recorded when the switch operated. Besides, when another 500kV intelligent substation starts, the electromagnetic disturbance signals are also recorded. The amplitude and time-frequency characteristics of the electromagnetic disturbance signals are analyzed. Based on the results of EMC experiments and the amplitude and time-frequency characteristics of disturbance signals, this paper analyzes the applicability of EMC test standard used in China. And it is pointed out that the test standard is not enough to check the field installation secondary intelligent device. Finally, some suggestions to improving the EMC performance of field installation secondary intelligent devices are put forward.

Effects of geometrical parameters on the performance of Rogowski coil for current measuring

Current measuring is the core precondition for relay protection, energy metering and Rogowski coil is one of the most favorable transformers. In this paper, the effects of geometrical parameters of Rogowski coil on its performance are calculated and compared to provide a general overview of geometrical selection. The expressions of mutual inductance of rectangular, circular and oval winding coil are derived and calculated, and the reliabilities of each shape of the coil are compared by the simulation. The results show that in condition of equal section area, the mutual inductance of rectangular, circular and oval winding coil are in descending sequences and the relative error of oval winding coil is the smallest, which is helpful for obtaining accurate current values. The research provides important guidance for the rapid and reasonable geometrical selection of Rogowski coil in engineering applications.

Comparison and analysis of protection latency time between intelligent and traditional substations

In this paper, the protection latency time between traditional and intelligent substations are compared and analyzed. In traditional substation, the analog information such as current and voltage are tranmitted to the protection and control devices via electric cable, while in intelligent substation the introduction of digital protection devices and intelligent substation prolong the protection time, which brings safe threaten to the cutoff of power system fault. The compositions of operation latency time are compared in each link and two major different time latency links are analyzed in details, and the mechanism of time latency is investigated and the effective meausures to reduce the protection latency time are proposed. Finally, the experiment of protection time comparison between two is carried out and the results prove the validity of theoretical analysis.

Research and application of load balance approach for distribution based on big data

For solving the common existence of feeder overload problem, a load balance approach based on big data is proposed in this paper. Because of the dynamic characteristics of distribution load, a feeder overload quantitative model is raised, while multi data sources are employed, such as total contents of feeder/distribution transformer load, grid fault information, business expanding plan, work/operation tickets etc. The approach changes the open/closed status of sectionalizing and tie switches of the overload feeder and its adjacent counterparts, calculates the comprehensive overload index of all the possible operation modes and chooses the most appropriate strategy. Example shows the effectiveness of this approach. This approach has been actually applied for the decision-making of Jiangsu distribution dispatching.

The study on the effects of the transformer Δ-side unbalanced third harmonic on the parallel capacitor bank caused by the sympathetic inrush current and the countermearsures

Under steady state condition, the third harmonic is thought to have the same features with zero-sequence component, which would not couple to the Δ-side device of the transformer. However, the field test result shows that the unbalanced third harmonic caused by the sympathetic inrush can flow into the Δ-side of the transformer. Hence, the third harmonic would form a loop with the capacitor at the low voltage side and may damage the capacitor and arrester. There is only zero-sequence component in the third harmonic under steady state condition. On the other hand, the third harmonic voltage and current caused by the sympathetic inrush are not symmetric; consequently, there are positive-sequence, negative-sequence and zero-sequence components. The positive-sequence and negative-sequence components in the sympathetic inrush would flow through the Δ-side of the transformer and flow into capacitor and load. Meanwhile, if the series reactance ratio of the parallel capacitor bank is 6%, there would be a series resonance point of the third harmonic, which is the reason of the amplification of the third harmonic. With theoretical analysis and simulation study, the above point of view is validated. Besides, a parallel capacitor bank with mixed series reactance is designed. The dynamic simulation test demonstrates that the parallel capacitor bank with mixed series reactance ratios can effectively suppress third harmonic and fifth harmonic. Hence, the parallel capacitor bank with mixed series reactance ratios is much better than the parallel capacitor bank with unified series reactance ratio.

The influences of message jitter on linear interpolation for electronic transformer data synchronization

In smart grid, the data synchronization of electronic transformer is the key precondition and guarantee for protection device to measure and operate accurately. In engineering application, the interpolation method is frequently applied to solve the synchronization problem. However, the sampling value message jitter of electronic transformer is usually caused due to the delay of network switch, the data packets line up mechanism and uncertainty of interrupt time, further resulting in the inaccuracy of interpolation method. In this paper, the influencing mechanism of message jitter on the interpolation accuracy is first analyzed, then the error expression of linear interpolation in the presence of jitter is deduced, and the influences of message jitter on linear interpolation accuracy is calculated at different sampling rates, harmonic frequency waves and jitter amplitudes. The simulation shows that the interpolating error increases with the increase of sampling rate and jitter amplitude, while the influences are relatively small on high harmonic frequency waves. The results provide important references for electronic transformer data synchronization application in the presence of message jitter.

A coordinated voltage control scheme for power system with large-scale wind power integration

To solve the technical problems about secure and stable operation of wind power integration, voltage control scheme for power system with large-scale wind farm integration is studied in this paper. A layered control structure for DFIG wind farm grid-connected system is designed. The control scheme and model of the system decision-making layer is presented to decide the task of wind farms on-line. Moreover, considering restriction and operation characteristic of DFIG, the control capability of wind farm may be evaluated, and wind farm control algorithm and strategy are proposed. Finally, the implementation of coordinated voltage control strategy for wind power grid-connected system is presented.