Analysis of power frequency electric field distortion caused by substation inspection robot

In the era of intellectualization, many substation inspection robots are being put into operation, but they will cause electric field distortion in the surrounding space during operation. This paper establishes a three-dimensional simplified simulation calculation model for 500kV substations and inspection robots. Based on the boundary element method, we simulate the power frequency electric field of the substation switchyard and analysis the distortion electric field when the inspection robot is in the station. The results show that when the electric field intensity is strong, the distortion coefficient caused by the robot will be larger, and the maximum can reach 2.25 times, and when the electric field intensity is small, the distortion coefficient will be smaller, and the distortion coefficient is 1.42 times on average.

Influence of Propeller Slipstream on the Flow Field of S-Shaped Intake

For turboprop engine, the S-shaped intake affects the engine performance and the propeller is not far in front of the inlet of the S-shaped intake, so the slipstream inevitably affects the flow field in the S-shaped intake and the engine performance. Here, an S-shaped intake with/without propeller is studied by solving Reynolds-averaged Navier-Stokes equation employed SST k-ω turbulence model. The results are presented as time-averaged results and transient results. By comparing the flow field in S-shaped intake with/without propeller, the transient results show that total pressure recovery coefficient and distortion coefficient on the AIP section vary periodically with time. The time-averaged results show that the influence of propeller slipstream on the performance of S-shaped intake is mainly circumferential interference and streamwise interference. Circumferential interference mainly affects the secondary flow in the S-shaped intake and then affects the airflow uniformity; the streamwise interference mainly affects the streamwise flow separation in the S-shaped intake and then affects the total pressure recovery. The total pressure recovery coefficient on the AIP section for the S-shaped intake with propeller is 1%-2.5% higher than that for S-shaped intake without propeller, and the total pressure distortion coefficient on the AIP section for the S-shaped intake with propeller is 1%-12% higher than that for the S-shaped intake without propeller. However, compared with the free stream flow velocity ( Ma = 0.527 ), the influence of the propeller slipstream belongs to the category of small disturbance, which is acceptable for engineering applications.

Appraisal of linear load effect on non-linear distortion coefficient from rectifier

Object and purpose of research. The object of research is the rectifier (transducer) OPED-12,5-115 (О – single phase; P – direct current; Е – natural air cooling; D – on diodes with an example of document record; 12.5 – current rating; 115 – voltage rating). Materials and methods. Methods of power electronics and harmonic analysis are applied. Main results. Ways of appraisal and restriction for the harmonic coefficient (non-linear distortion coefficient from transducer) are worked out taking account of an active load of higher frequencies generator (400 Hz). Conclusion. Numerical estimations for the attenuation coefficient of harmonics 3, 5 and 7 are obtained using basic values Xd and Xq of generator АТО-20.

DEPENDENCIES OF THE DISTORTION FACTOR OF THE SINUSOIDALITY OF THE RECOVERY CURRENT ON THE PARAMETERS OF THE PROCESS WHEN CONTROLLING THE FORCED DISCHARGE OF ACCUMULATOR BATTERIES INTO THE NETWORK BY SIGNAL WITH SINGLE-CYCLE ONE-WAY PULSE-WIDTH MODULATION

For modern remote and closed systems of uninterruptible power supply, a operation of forced discharge of accumulator batteries is in demand. It is advisable to carry out the specified process of forced discharge with recuperation into the network. This way of leads: firstly, to a decrease in the mass of charging and discharging devices due to the exclusion of powerful resistive loads from the latter; secondly, to noticeable energy savings for closed autonomous objects. At the same time, for the regenerative current, increased requirements are imposed on its sinusoidality, the distortion coefficient of which is significantly influenced by the relationship between the EMF of the battery and the amplitude of the mains voltage, the discharge current and the maximum current of the coil of the active rectifier. The influence the frequency of the PWM control signal and the frequency of the regeneration current (mains frequency) is also possible. In uninterruptible systems, storage batteries are used with different total EMF and capacity that determines the discharge current. In addition, the mentioned values change during operation, and at forced discharge, various technique can be used that differ in the ratio of the discharge current to the capacity of the battery and the law of its change. Therefore, in the development of a universal system for forced discharge of a battery into a network with pulse-width control of the regenerative current shape, is relevant information on the dependences of the distortion factor of the sinusoidality on the above ratios of the battery voltage and the amplitude of the mains voltage, the discharge current and the maximum current of the coil of the active rectifier coil, as well as from the number of pulses for the regeneration current period. The article presents the results of work on obtaining diagrams of these dependencies. To obtain the latter, the function of the output current of the active rectifier is formed – of the regeneration current, then its spectral function. Using the latter, the current waveform distortions are estimated based on the spectral approach. The results obtained are in demand in the development of program modules for microcontrollers of the pulse-width regulators of the regeneration current, which implement algorithms for the formation of a current curve with acceptable values of the distortion coefficient of the sinusoidality when changing the parameters of the battery, network and discharge current.

Experimental and numerical investigation on total pressure distortion generated by a rectangular movable flat baffle

A distortion generator equipped with a motor-activated movable flat baffle was installed just upstream of a rectangular plenum entrance to investigate the effects of inlet total pressure distortion on the stability and performance of an auxiliary power unit (APU). Experiments and numerical simulations on a direct connect scale inlet model of the APU were carried out to obtain a quantitative relationship between the insertion depth of the flat baffle in the flow stream and the total pressure distortion intensity and region. In the experiments, the blocking coefficient and total pressure distortion coefficient were controlled by adjusting the insertion depth of the flat baffle and the mass flow. In the simulations, detailed flow field was analyzed based on the detached-eddy simulation (DES) method. The results show that the pressure distribution of the distorted flow on the aerodynamic interface plane (AIP) can be divided into a high-pressure region, a transition region, and a low-pressure region. The area affected by the distorted flow was larger than the inserting area of the flat baffle. That area was more related to the relative blocking coefficient, and less affected by the mass flow. The total pressure distortion coefficient had a linear relationship with the mass flow rate and is positively correlated with the relative blocking coefficient. As the relative blocking coefficient increased to a certain value, an exponential growth in the total pressure distortion coefficient occurred, and consequently, the flow field distortion was intensified. In the flow field, a pair of corner vortices were formed at the corner between the flat baffle and the bottom wall of the inlet pipe, and a large separation zone was formed behind the flat baffle and exhibits certain unsteady characteristics.

Aerodynamic Comparison Between Circumferential and Wing-Embedded Inlet Distortion for an Ultra-High Bypass Ratio Fan Stage

Future aircraft design concepts often show a somewhat wing embedded ultra-high bypass ratio engine. The aircraft concept of the Coordinated Research Centre 880 (CRC880) is a single-aisle configuration with engines partly integrated over the aircraft wing. The aircraft is designed to take off and land on regional airfields with low noise and fuel emissions to address the guidelines set by the ACARE. As a result of the engine installation, the inlet induces a non-axisymmetric boundary layer ingestion into the fan stage. In experimental setups, inlet distortion has often been seen as a 60-degree circumferential inlet stagnation pressure distortion. However, the fan stage inlet flow of the prescribed engine installation of the CRC880 differs to a great extent from a 60-degree sector. In this paper, an aerodynamic comparison between a realistic inflow situation and a similar 60-degree inlet distortion for the same ultra-high bypass ratio fan stage is given. The realistic inflow situation is a result of the flow moving over the aircraft wing suction side and entering the nacelle. As non-axisymmetric inlet geometry remains the same for both cases, therefore, only the total pressure boundary condition at nacelle inlet was changed between both cases. Hence, full annulus simulations are required. Both inlet distortion cases are equivalent by matching average 60-degree distortion coefficient. This study points out that the method, by using averaged 60-degree segment values, excludes specific inflow characteristics. For the same averaged 60-degree distortion coefficient, the local distortion of the embedded case is up to four times larger at rotor tip compared to the segmental approach. For constant mass flow, fan pressure ratio and isentropic efficiency drop by more than five and eight percent respectively. At peak efficiency operating condition, the decrease is even more significant with more than nine percent in stage efficiency. For future embedded aircraft engine configurations, the fan designer has to take into account the non-axisymmetric local flow changes. Hence, the 60-degree segment method is not sufficient when investigating experimental boundary layer ingesting fans and therefore, further method developments are necessary.

Comparative Study on the Performance of S-Shaped Diffuser With Shorten Length

This study presents numerical investigation on the performance of S-shaped air intake normal and aggressive diffuser with 22% length reduction. Both models have same area ratio of 3.1 with different total length, turning angle and radius of curvature. The numerical investigation was implemented using CFD simulation by ANSYS-FLUENT 15 software. The inlet Reynold number was 4×104 and turbulence intensity 4.1%. The performance evaluation was performed throw evaluation the static pressure coefficient, pressure loss coefficient, distortion coefficient and static pressure wall coefficient. The numerical results show that the performance in the case of aggressive S-shaped diffuser has been reduced compared to the normal S-shaped diffuser. This reduction resulting from the early flow separation and increase of the separation zone due to the high curvature of top and bottom surfaces of aggressive S-shaped diffuser. The results show that the static pressure recovery coefficient decreased by 31%, the total pressure loss coefficient and distortion coefficient increased by 9.5% and 8.2%, respectively, compared to the S-shaped diffuser. The static pressure wall coefficient on the top and bottom surfaces was dropped with the aggressive S-shaped diffuser.