CHAPTER 4: Experiemental results & Discussion
4.4 Strain of suspension insulator
70
Figure 4-12: ACSR Tern conductor held by the suspension clamp: bending amplitudes vs. vibrational loads
Table 4-1: ACSR Pelican conductor: vibrational loads at 1.0 mm (peak-to-peak) UTS
(%)
Vibrational loads (N) Blocked
clamp
Articulated clamp
With insulator
15 164 105 99
20 217 142 137
25 278 160 162
30 288 180 182
Table 4-2: ACSR Tern conductor: vibrational loads at 1.0 mm (peak-to-peak) UTS
(%)
Vibrational loads (N) Blocked
clamp
Articulated clamp
With insulator
15 320 228 187
20 380 307 265
25 402 390 342
30 476 447 435
71
4.4.1 Static measurement of the strain of the insulator
This depicts the static measurement of the strain gauges of the suspension insulator loaded gradually with 100 N till it reaches 800 N. It has been noted that the FRP rod of the insulator close to the end fittings was less sensitive to the axial tensile loads than the FRP rod in the middle of the suspension insulator (Figure 4-13). Gauges 1 and 3 seemed to have the same strain behaviour in contrast with gauge 2 which increased rapidly to the first 400 N that was applied. In the middle of the insulator (gauge 2) there is more mechanical stresses (tensile) than the FRP area closed to the two end- fittings of the composite insulator (gauges 1 & 3). The maximum tensile load applied was almost 750 N which represents 0.625% of SML.
Figure 4-13: Location and numbering of strain gauges and the static measurement of the strain on the FRP rod of the suspension insulator
4.4.2 ACSR Pelican: Strain of the suspension insulator
The dynamic measurement of the strain gauges attached on the surface of the FRP rod of the suspension insulator has displayed behaviour differing from the static measurement. The tests were conducted at two different frequencies. The vibrational loads on the suspension were acting axially on the suspension insulator.
Figure 4-14 interprets the mechanical behaviour of the insulator by the strain generated at different frequencies. At 9.25 Hz, the strain increased slightly as a function of the peak-to-peak bending amplitudes of 0.1 mm increment on each level. For the
0 100 200 300 400 500 600 700 800
0 5 10 15 20 25 30 35 40 45
Load applied (N)
Strain (Microstrains)
Static strain measurement of FRP rod of the suspension insulator
Gauge 1 Gauge 2 Gauge 3
72
measurement conducted at 15.13 Hz, the same increment was observed until the 0.8 mm peak-to-peak bending amplitude; and at 0.9 mm the strain increased dramatically. It appeared apparently that the second frequency measurement of the vibrating conductor increased the effect of dynamic loads (No damping effect) on the composite insulator. Further study should be investigated on the reason of this increment as both the conductor and the composite insulator do not have same resonance frequency.
Figure 4-14: Dynamic strain of the FRP rod of insulator vs. the bending amplitudes of the ACSR Pelican conductor at 15% UTS
Figure 4-15: Dynamic strain of the FRP rod of insulator vs. the bending amplitudes of the ACSR Pelican conductor at 20% UTS
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0 20 40 60 80 100 120 140
Peak-to-peak bending amplitude (mm)
Peak-to-peak strain (microstrains)
15%UTS - ACSR Pelican conductor Suspension insulator configuration
Gauge 1 (9.25Hz) Gauge 2 (9.25Hz) Gauge 3 (9.25Hz) Gauge 1 (15.13Hz) Gauge 2 (15.13Hz) Gauge 3 (15.13Hz)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0 10 20 30 40 50 60
Peak-to-peak bending amplitude (mm)
Peak-to-peak strain (microstrains)
20%UTS - ACSR Pelican conductor Suspension insulator configuration
Gauge 1 (9.14Hz) Gauge 2 (9.14Hz) Gauge 3 (9.14Hz) Gauge 1 (15.37Hz) Gauge 2 (15.37Hz) Gauge 3 (15.37Hz)
73
Figure 4-16: Dynamic strain of the FRP Rod of insulator vs. the bending amplitudes of the ACSR Pelican conductor at 25% UTS
Figures 4-15 (20% UTS) and 4-16 (25% UTS) show the strain curves of the FRP rod of the insulator increasing steadily while the ACSR Pelican was vibrating.
Referring to the graph 4-17, at 30% UTS, the peak-to-peak values of the FRP rod strain measured at 10.1 Hz has increased moderately, seeming to be linear, however, at 0.1 mm and 1.0 mm, the strains have considerably increased at 15.25 Hz.
Figure 4-17: Dynamic strain of the FRP rod of insulator vs. the bending amplitudes of the ACSR Pelican conductor at 30% UTS
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0 5 10 15 20 25
Peak-to-peak bending amplitude (mm) Peak-to-peak bending strain (microstrains) 25%UTS - ACSR Pelican conductor
Suspension insulator configuration
Gauge 1 (9.51Hz) Gauge 2 (9.51Hz) Gauge 3 (9.51Hz) Gauge 1 (16.09Hz) Gauge 2 (16.09Hz) Gauge 3 (16.09Hz)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0 10 20 30 40 50 60 70 80
Peak-to-peak bending amplitude (mm)
Peak-to-peak strain (microstrains)
30%UTS - ACSR Pelican conductor Suspension insulator configuration
Gauge 1 (10.10Hz) Gauge 2 (10.10Hz) Gauge 3 (10.10Hz) Gauge 1 (15.25Hz) Gauge 2 (15.25Hz) Gauge 3 (15.25Hz)
74 4.4.3 ACSR Tern: Strain of the insulator
Figures 4-18, 4-19 and 4-20 show the axial strain of the FRP rod of the suspension insulator generated by the vibration of the ACSR Tern conductor under the chosen frequencies.
Figure 4-18: Dynamic strain of the FRP Rod of insulator vs. the bending amplitudes of the ACSR Tern conductor at 15% UTS
Figure 4-19: Dynamic strain of the FRP Rod of insulator vs. the bending amplitudes of the ACSR Tern conductor at 20% UTS
At 25% UTS of the ACSR Tern conductor, all strains measured at both frequencies started to increase gradually, continuing to 1.0 mm bending amplitude (Figure 4-20). At 30% UTS, only the strain measured by strain gauge 3 at 15.25 Hz had increased
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0 10 20 30 40 50 60
Peak-to-peak bending amplitude (mm)
Peak-to-peak strain (microstrains)
15%UTS - ACSR Tern conductor Suspension insulator configuration
Gauge 1 (8.64Hz) Gauge 2 (8.64Hz) Gauge 3 (8.64Hz) Gauge 1 (15.61Hz) Gauge 2 (15.61Hz) Gauge 3 (15.61Hz)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0 10 20 30 40 50 60
Peak-to-peak bending amplitude (mm)
Peak-to-peak strain (microstrains)
20%UTS - ACSR Tern conductor Suspension insulator configuration Gauge 1 (7.43Hz)
Gauge 2 (7.43Hz) Gauge 3 (7.43Hz) Gauge 1 (15.40Hz) Gauge 2 (15.40Hz) Gauge 3 (15.40Hz)
75
strongly, while all other strains measured for both frequencies increased gradually but only slightly, without any disturbance.
Figure 4-20: Dynamic strain of the FRP Rod of insulator vs. the bending amplitudes of the ACSR Tern conductor at 25% UTS
Figure 4-21: Dynamic strain of the FRP Rod of insulator vs. the bending amplitudes of the ACSR Tern conductor at 30% UTS