67 Figure 5.6: Temperature variation of the messenger cable damper at the attached point of bulk (Tc1) as a function of excitation frequency at constant speed. 69 Figure 5.8: Temperature variation of the messenger cable damper at the point of small mass capture (Tc3) as a function of excitation frequency at constant speed. 70 Figure 5.9: Temperature variation of messenger cable damper at small mass attachment point (Tc4) as a function of excitation frequency at constant speed.
73 Figure 5.12: Temperature variation of the damper's messenger cable at the clamping point of the small mass (Tc3) as a function of excitation frequency at constant displacement.
INTRODUCTION
Statement of the problem
Being able to withstand large voltages is an amazing property of a conductor, which is why conductors or cables are used as overhead transmission lines. Overhead transmission lines are highly exposed to wind forces, causing them to vibrate. The types of vibrations are aeolian, galloping or wake-induced, depending on the intensity of the wind.
The largest investment component of power transmission is the conductor, so they must be protected from wind-induced vibrations.
Aims and Objectives
Cables or conductors are widely used in various engineering structures such as bridges, overhead transmission lines, guide poles and other structures where high voltages are involved. Stockbridge dampers are used to dampen the vibrations of line conductors, but they are subject to the same unwanted and destructive effects of vibration as the conductors they are intended to protect.
Research publication
Brief chapter overviews
Efficiency of the Stockbridge damper as a function of the messenger cable length L and the weight mass was also determined (Figure 3.10). Results of the free vibration test of the Stockbridge damper are presented in this section. Four accelerometers (Rect 2, 3, 4 and 5) on the damper masses, two on each mass to detect each vibration mode of the Stockbridge damper;.
N 6974fres The correlation between the load on the messenger cable near the terminals at the short side of the Stockbridge damper and the resonant frequency is given by Equation 5.35. 99 (5.35) where: is the load on the messenger cable near the clamp at the short side of the Stockbridge damper. The ratio of the acceleration of the small mass of the damper during the fatigue test and.
The Stockbridge damper damage model was established based on the fourth resonance frequency change ratio.
POWER LINE MOTION
Introduction
Shedding phenomenon
Classification of overhead power line motion
- The Aeolian vibration
- The galloping of power line
- The wake induced vibration
The primarily vertical movement of power lines with a low frequency and high amplitude is called galloping. The galloping phenomenon is caused by the freezing temperature of the air, which forms ice on the power line when the wind blows. The force that the wind transfers to the power line in this way is greater than that from aeolian vibrations.
Moderate to strong crosswinds generated by dumping cause cyclic bending of transmission lines.
Comparison of different power line motion
Mitigate the power line vibrations
- Spiral dampers
- Bretelle dampers
- Festoon dampers
- Stockbridge damper
- Haro damper
- Dogbone Damper
LITERATURE REVIEW
Engineering vibration
- Analysis of mechanical vibration
- Classification of mechanical vibration
The damping element c (Figure 3.1) is also a solid mass and has no elasticity. Classification of mechanical vibrations can be done using the system shown in Figure 3.1. Some important classifications are presented in the paragraph below. A forced vibration of a system is one that occurs when the system is subjected to an external force.
One result of forced vibration is a resonant frequency at which the system undergoes dangerous oscillation.
Mechanical behavior of Stockbridge Damper
Calculations of the energy input by the wind to the conductor and the energy lost from the conductor were also determined. The analysis of the Aeolian vibration of a conductor with a damper was studied by Vecchiarelli et al. Dmax is the function value that gives the maximum bending stress of the messenger cable.
The approach for optimizing the parameters of the Stockbridge damper was proposed by Navarro-Canales et al.
Damage in mechanical engineering
- Introduction
- Structural damage detection
- Cumulative fatigue damage
- Damage models for Stockbridge dampers
Based on the analytical theory of the loaded spring, they used the modal frequency for experimental damage detection in structures. For this, White et al. 2009) examined the repair of debris and verified the repair status of the original repair and found that in both cases damage could be detected by a change in resonance frequency. Where K0 is the empirical material coefficient for the new component, D0 is the durability of the new material.
The endurance of material is function of the damage of the component and its changing variation is a function of K.
Remaining life assessment
- Introduction
- Remaining life
- Approach for remaining life
The temperature variation was determined as the difference between the initial temperature and the final temperature of the messenger cable. These temperature variations can be estimated around the second resonance frequency of the Stockbridge damper.
MATERIAL AND METHODS
Auxiliary Equipment
- Shaker, amplifier and controller
- Accelerometer
- Strain gauges
A strain gauge is a sensor used to measure the strain on the surface of the object during the experiment. A strain gauge is characterized by gauge dimensions, gauge factor, gauge resistance, gauge pattern, gauge series, range, temperature and self-temperature compensation. Gauge dimension: The length and width of the grid determine the length and width of the strain gauge, respectively (Figure 4.4).
These are the main dimensions of the strain gauge as they relate to the dimensions of the main part. Gauge Resistance: The resistance of a strain gauge is the resistance measured between the two metals used for the connection. The strain gauge with a gauge resistance of 120 ohms is the most popular in terms of and the most produced is the one with 350 ohms which is also used in transducers.
Range: The range of a strain gauge is defined as the maximum strain the gauge can measure without resetting or replacing it. Temperature: The strain gauge's properties as well as the material's properties to which the strain gauge is glued can be changed by temperature. Self-temperature expansion: This characteristic is related to the materials where the extensometer will be used.
Therefore, the Wheatstone bridge is used to measure small resistance changes in the strain gauge. The strain gauges and the amplifier module for the strain gauge used during the experiment are shown in Figure 4.7.
Tests of Stockbridge damper and experimental set up
- Standard tests of Stockbridge damper
- Fatigue test
The change in the resonant frequency of the Stockbridge damper is a function of the degree of damage to the Stockbridge damper. The temperature variation of the messenger cable was measured during the forced response test at constant displacement and speed.
EXPERIMENTAL RESULTS AND DISCUSSION
Symmetrical damper
- Experiment set up and methods
- Model description
- Results and discussion
Strain gauges (half-circuits) (Hoffmann, 1987) were placed on both sides of the message cable near the clamped end. The two accelerometers allowed measurement of the two modes of vibration of the Stockbridge damper (mode one and mode two) during sweep. The messenger cable tension data was adjusted by the MP55 strain gauge amplifier, and the data from the accelerometers was captured by the PUMA control systems software.
The Young's modulus of the messenger cable was determined using Solid Edge after determining the density of the messenger cable. In this thesis, the model presented by Wagner et al. 1973) is used due to the availability of the required properties of the damper. During the vibration of a Stockbridge damper, the motion of the damper weight is characterized by two degrees of freedom: the alternate motion of translation, y, and the rotation, (Figure 5.2).
In the above three expressions, δ is the logarithmic attenuation of the damper messenger cable while, f, f1, f2 represent the driving frequency, the first resonant frequency and the second resonant frequency. Axial acceleration x and angular acceleration are obtained from the second derivative of the axial and angular displacement, respectively. The bending moment of the MB messenger cable at the cable attachment point is calculated using the sum of all torques on the link damper.
From 14 Hz to 27 Hz the gap between the curves is created by the interactions of the two forms of damper vibration. However, the curve from the experiment is the rotation of the curve from the model with the peak as the center of rotation.
Asymmetrical damper
- Temperature variation of messenger cable
- Free vibration test
- Forced response and fatigue test
The fourth mode was simulated during the hammer free vibration test on the damper (5.16 b) at the end of the small mass. A correlation was established which describes the relationship between the resonance frequency and the acceleration of the small mass. It was observed that the fourth resonance frequency of the Stockbridge damper changed with the number of cycles passed, as well as the acceleration of the small mass including the tension in the messenger cable near the clamp.
These causes of failure began with the appearance of cracks on the wire of the messenger cable. The approach to determine the remaining lifetime is presented using a regression after obtaining the fourth resonance frequency of the Stockbridge damper. Investigation of the stiffness variations of the Stockbridge damper as a function of the number of cycles elapsed.
CONCLUSION AND RECOMMENDATIONS
Conclusion
This approach involves collecting data such as acceleration, resonant frequency and strain measurement to predict the life and remaining life of the Stockbridge damper. The same experimental and mathematical procedure can be used to determine the bending stress of the message cable at other locations, such as those near the center of gravity. Due to friction between the wires of the relay cable, a temperature fluctuation was observed on the relay cable of the valve during operation and testing of the valve.
Also, the temperature of the messenger cable during the test was investigated in the frequency range of wind-induced vibration of the symmetrical damper. As a result, the highest temperature change (2.8 K) was observed at the constant velocity peak at the peak near the point of attachment of the large mass on the messenger cable. The most common failure mode, which is the loss of small mass of the damper, was investigated.
By correlation, a mathematical model was established taking into account the resonance frequencies, the acceleration of the damper's small mass, and the stresses on the messenger cable near the clamp on the small mass side of the Stockbridge damper. It was discovered that the main reason for loss of the small mass was the friction between wires at the junction between the messenger cable and the mass. In the failure process, the stiffness and damping capacity of the Stockbridge damper decays and therefore the resonance frequencies also decay.
This involves determining Stockbridge damper life as a function of stiffness. Investigating real-time and state-of-the-art Stockbridge damper life prediction using in situ data.
