scholarly journals Adaptive Configuration Method of Low-Frequency Electromechanical Sampling Information in Building Electrical System

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Bai Yu ◽  
Zhixin Zhang
Keyword(s):  
Information Acquisition ◽  
Damping Ratio ◽  
Low Frequency ◽  
Phase Method ◽  
Stable Operation ◽  
Reference Channel ◽  
Electrical System ◽  
Series Compensation ◽  
Stochastic Subspace Identification ◽  
Value Decomposition

In order to enhance the reliability of the electrical systems in low frequency, an adaptive configuration method of low-frequency electromechanical sampling information based on thyristor controlled series compensation (TCSC) is designed. The electrical system is simplified to a linear invariant system, and a stochastic subspace identification (SSI) method is established by using the singular value decomposition principle to collect low-frequency electromechanical sampling information. The reference channel technology is introduced to design the reference channel covariance matrix to judge whether low-frequency information is generated and improve the efficiency of sampling information acquisition. The architecture and working principle of the controllable series compensation device are analyzed, and the test signal method is used to evaluate the low-frequency modes and the information required by the device among the electrical system regions of buildings. The alternative input signals are selected by comparing different input signal residue ratios. The TCSC device parameters are adjusted by the compensation residue phase method, so as to realize the adaptive configuration of different low-frequency electromechanical sampling information and ensure the stable operation of the electrical system. The experimental results show that the proposed configuration scheme can effectively improve the damping ratio of the system and has an excellent effect on suppressing the continuous oscillation under a low-frequency fault.

Dynamic Stability of a Water Brake Dynamometer

1998 ◽  
Vol 120 (1) ◽  
pp. 89-96 ◽  
Author(s):  
R. A. Van den Braembussche ◽  
H. Malys
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Lumped Parameter Model ◽  
Stable Operation ◽  
Pressure Oscillations ◽  
Lumped Parameter ◽  
Flow Oscillations ◽  
Brake Dynamometer ◽  
Low Torque ◽  
Frequency Variations

A lumped parameter model to predict the high frequency pressure oscillations observed in a water brake dynamometer is presented. It explains how the measured low frequency variations of the torque are a consequence of the variation in amplitude of the high frequency flow oscillations. Based on this model, geometrical modifications were defined, aiming to suppress the oscillations while maintaining mechanical integrity of the device. An experimental verification demonstrated the validity of the model and showed a very stable operation of the modified dynamometer even at very low torque.

scholarly journals An Image Denoising Method with Enhancement of the Directional Features Based on Wavelet and SVD Transforms

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Min Wang ◽  
Zhen Li ◽  
Xiangjun Duan ◽  
Wei Li
Keyword(s):  
Wavelet Transform ◽  
Singular Value Decomposition ◽  
Image Denoising ◽  
High Frequency ◽  
Low Frequency ◽  
Singular Value ◽  
Denoising Method ◽  
Diagonal Part ◽  
Value Decomposition ◽  
Image Part

This paper proposes an image denoising method, using the wavelet transform and the singular value decomposition (SVD), with the enhancement of the directional features. First, use the single-level discrete 2D wavelet transform to decompose the noised image into the low-frequency image part and the high-frequency parts (the horizontal, vertical, and diagonal parts), with the edge extracted and retained to avoid edge loss. Then, use the SVD to filter the noise of the high-frequency parts with image rotations and the enhancement of the directional features: to filter the diagonal part, one needs first to rotate it 45 degrees and rotate it back after filtering. Finally, reconstruct the image from the low-frequency part and the filtered high-frequency parts by the inverse wavelet transform to get the final denoising image. Experiments show the effectiveness of this method, compared with relevant methods.

Lateral Stability of Road and Rail Trailers

1969 ◽  
Vol 91 (4) ◽  
pp. 1069-1074 ◽  
Author(s):  
W. B. Diboll ◽  
D. H. Hagen
Keyword(s):  
Degrees Of Freedom ◽  
Damping Ratio ◽  
Stable Operation ◽  
Lateral Stability ◽  
Energy Term ◽  
Lower Velocity ◽  
Pivot Point ◽  
Dimensionless Energy ◽  
Excited Vibration ◽  
Angular Displacements

The conditions for the lateral stability at a highway or rail trailer are investigated analytically and experimentally with a laboratory size trailer. The motion of the trailer is expressed in two degrees of freedom, the lateral and angular displacements of the trailer. The oscillation was found to be a self-excited vibration which is very dependent upon the lateral springing at the towing pivot point. The variables are expressed as dimensionless parameters. For conventional trailer loading, the most important variables are the damping ratio as a function of the Strouhal number, sω/V, and as a function of a dimensionless energy term, μGz/V2. As higher values of sω/V and μGz/V2 are reached (for example, lower velocity), less damping is needed for stable operation. Although the relationships have not been established precisely, there is good correlation.

Analysis of Low Frequency Oscillation in Interconnected Power System under Hedge Operation Mode

2014 ◽  
Vol 536-537 ◽  
pp. 1542-1546
Author(s):  
Xun Gao ◽  
Jie Meng ◽  
Yi Qun Li ◽  
Ying Wang ◽  
Wen Chao Zhang
Keyword(s):  
Power System ◽  
Power Flow ◽  
Power Grid ◽  
Damping Ratio ◽  
Operation Mode ◽  
Oscillation Mode ◽  
Low Frequency ◽  
Operating Mode ◽  
Low Frequency Oscillation ◽  
Interconnected Power System

A phenomenon that the damping ratio will decrease when the power flows from both sides to the primary power grid is summarized and analyzed in the paper. Based on analysis of the damping ratio change of West Inner Mongolia-Shandong oscillation under the sequential operation mode and the hedge operation mode, a three-machine equivalent system is established to study edge to edge (ETE) oscillation mode under hedge operating mode of the power system. The influence of magnitudes and trends of power flow on damping ratio is analyzed, and the reason that why damping ratios decreases when both sides send power to the mid-side power grid is explained.

Impact of Large Scale Wind Power Transmission on System Dynamic Stability

2013 ◽  
Vol 448-453 ◽  
pp. 2535-2539
Author(s):  
Jun Cheng ◽  
Qiang Yang ◽  
Tao Zhu ◽  
Ai Meng Wang ◽  
Xue Feng Hu ◽  
...  
Keyword(s):  
Power System ◽  
Dynamic Stability ◽  
Large Scale ◽  
Wind Farm ◽  
System Analysis ◽  
Power Transmission ◽  
Damping Ratio ◽  
Wind Farms ◽  
Stable Operation ◽  
Large Area

With the scale of the wind farm growing fast, its impact on the power system has become increasingly apparent. So the research has a significant meaning on the characteristics of dynamic stability of the power system which contains wind farms, and the stable operation of the large area interconnected power grid. In this paper it realized the application of the double-fed wind turbine grid model by using power system analysis software PSD-BPA. The analysis of the generator power Angle curve which indicate the state after the failure of N-1 shows as follows: with the wind farms integration on the grid, the damping ratio is decreased slightly but little change after the system failure of N-1, which is still live up to the standard of grid stability.

scholarly journals PCBs Contamination among Distribution Transformers in the Kathmandu Valley

2015 ◽  
Vol 4 (1) ◽  
pp. 16-29 ◽  
Author(s):  
Ruska Kattel ◽  
Bhupendra Devkota
Keyword(s):  
Low Frequency ◽  
Soil Surface ◽  
Transformer Oil ◽  
Kathmandu Valley ◽  
Electrical System ◽  
Tonal Noise ◽  
Distribution Centre ◽  
Distribution Transformers ◽  
The Status ◽  
Crucial Part

Transformer is the crucial part in any electrical system, however there are many risks associated with its use. Thus this study was focused on assessing the status of PCBs contamination and distribution of transformers in Distribution Centre-North of the Kathmandu valley along with PCBs contamination in them. Each transformer within the study area was closely observed to obtain information about all transformers. The dielectric oil samples from the transformers were collected, safely stored and analyzed in Test Kits (L2000DX Chloride Analyzer System, recommended by UNEP). Among 111 samples of transformer oil analyzed, 4 transformers were found PCBs contaminated and they were manufactured before 1990s. The total amount of PCBs contaminated transformer oil in these transformers was 479.6 Kg. Seven transformers were found leaking, four transformers located at residential area were found emitting a low frequency tonal noise, two transformers were located within school compound, nine transformers were located near water body and around 1.44 square meters of soil surface was found contaminated by transformer oil. Though there is no way to eliminate all the risk and consequences of operating oil filled transformers, scientific distribution and proper handling could be the reasonable approaches to reduce the risks.DOI: http://dx.doi.org/10.3126/ije.v4i1.12175International Journal of Environment Volume-4, Issue-1, Dec-Feb 2014/15, Page: 16-29

Transient Compressional Waves in an Infinite Elastic Plate or Elastic Layer Overlying a Rigid Half-Space

1962 ◽  
Vol 29 (1) ◽  
pp. 53-60 ◽  
Author(s):  
Julius Miklowitz
Keyword(s):  
Half Space ◽  
Elastic Layer ◽  
Integral Transform ◽  
Formal Solution ◽  
Equations Of Motion ◽  
Low Frequency ◽  
Frequency Equation ◽  
Point Load ◽  
Phase Method ◽  
Stationary Phase Method

The problem treated is that of an infinite free plate excited symmetrically by two equal and normally opposed step point-loads on its faces. The problem is equivalent to that of the surface normal point-load excitation of an infinite elastic layer, half the thickness of the plate, overlying a rigid half-space with lubricated contact. The formal solution is obtained from the equations of motion in linear elasticity with the aid of a double integral transform technique and residue theory. The stationary phase method, and known characteristics of the governing Rayleigh-Lamb frequency equation, are used to analyze and evaluate numerically the far field displacements. It is shown that the head of the disturbance is composed predominantly of the low-frequency long waves from the lowest mode of wave transmission.

scholarly journals Experimental Investigation on Cavitating Flow Induced Vibration Characteristics of a Low Specific Speed Centrifugal Pump

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Bo Gao ◽  
Pengming Guo ◽  
Ning Zhang ◽  
Zhong Li ◽  
Minguan Yang
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Local Maximum ◽  
Cavitation Number ◽  
Cavitating Flow ◽  
Vibration Characteristics ◽  
Vibration Energy ◽  
Stable Operation ◽  
Centrifugal Pumps ◽  
Number Range

Cavitating flow developing in the blade channels is detrimental to the stable operation of centrifugal pumps, so it is essential to detect cavitation and avoid the unexpected results. The present paper concentrates on cavitation induced vibration characteristics, and special attention is laid on vibration energy in low frequency band, 10–500 Hz. The correlation between cavitating evolution and the corresponding vibration energy in 10–500 Hz frequency band is discussed through visualization analysis. Results show that the varying trend of vibration energy in low frequency band is unique compared with the high frequency band. With cavitation number decreasing, vibration energy reaches a local maximum at a cavitation number much larger than the 3% head drop point; after that it decreases. The varying trend is closely associated with the corresponding cavitation status. With cavitation number decreasing, cavitation could be divided into four stages. The decreasing of vibration energy, in particular cavitation number range, is caused by the partial compressible cavitation structure. From cavitation induced vibration characteristics, vibration energy rises much earlier than the usual 3% head drop criterion, and it indicates that cavitation could be detected in advance and effectively by means of cavitation induced vibration characteristics.

Validation of Measured Dynamic Data Using Rigid Body Response

2012 ◽  
Vol 55 (1) ◽  
pp. 25-39
Author(s):  
David Smallwood
Keyword(s):  
Rigid Body ◽  
Low Frequency ◽  
Linear Combinations ◽  
Resonant Frequencies ◽  
Low Frequencies ◽  
Spectral Density Matrix ◽  
Rigid Body Modes ◽  
Linear Fit ◽  
Value Decomposition ◽  
Body Response

As multiple axis vibration testing has become more widespread, it has become increasingly important to ensure the instrumentation is accurately portrayed in the instrumentation table. However, errors do occur. The method used in this paper to help uncover these errors is based on the condition that at low frequencies (below any resonant frequencies of the object being studied) the response is essentially rigid body. The spectral density matrix (SDM) at a low frequency, of many more than six response measurements, is decomposed using singular value decomposition (SVD). Under the assumption of rigid body response, it is assumed that the first six singular vectors are linear combinations of the six rigid body modes. The best linear fit is then calculated for this fit. The measurements are then removed one at a time, and the reduction in the fit error is calculated. It is assumed that if the removal of a measurement reduces the error significantly, that measurement is likely in error.

scholarly journals Damping Effects Induced by a Mass Moving along a Pendulum

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
E. Gandino ◽  
S. Marchesiello ◽  
A. Bellino ◽  
A. Fasana ◽  
L. Garibaldi
Keyword(s):  
Linear Time ◽  
Damping Ratio ◽  
System Response ◽  
Time Varying ◽  
Simple Method ◽  
Equivalent Damping ◽  
Stochastic Subspace Identification ◽  
Time Varying Systems ◽  
Instantaneous Frequencies ◽  
Short Time

The experimental study of damping in a time-varying inertia pendulum is presented. The system consists of a disk travelling along an oscillating pendulum: large swinging angles are reached, so that its equation of motion is not only time-varying but also nonlinear. Signals are acquired from a rotary sensor, but some remarks are also proposed as regards signals measured by piezoelectric or capacitive accelerometers. Time-varying inertia due to the relative motion of the mass is associated with the Coriolis-type effects appearing in the system, which can reduce and also amplify the oscillations. The analytical model of the pendulum is introduced and an equivalent damping ratio is estimated by applying energy considerations. An accurate model is obtained by updating the viscous damping coefficient in accordance with the experimental data. The system is analysed through the application of a subspace-based technique devoted to the identification of linear time-varying systems: the so-called short-time stochastic subspace identification (ST-SSI). This is a very simple method recently adopted for estimating the instantaneous frequencies of a system. In this paper, the ST-SSI method is demonstrated to be capable of accurately estimating damping ratios, even in the challenging cases when damping may turn to negative due to the Coriolis-type effects, thus causing amplifications of the system response.

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