Analysis On Electrical And Mechanical Properties Of Cable Insulation With NANO Composites

ASAR International Conference, Coimbatore Chapter- 12th May 2013, ISBN: 978-81-927147-4-5

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ANALYSIS ON ELECTRICAL AND MECHANICAL PROPERTIES OF CABLE INSULATION WITH NANO COMPOSITES

P.JAYANTHI, C. PUGAZHENDHI SUGUMARAN

Department of High Voltage Engineering, College of Engineering Guindy, Anna University, Chennai, India

Abstract— Cable insulation plays a vital role in manufacturing of cables depending upon the type of rating. Different parameters conditions were considered for better insulation of the cables like it should possess better dielectric and mechanical properties. The dielectric strength of cable insulation mainly depends upon the existence of filler material. In this work, laboratory studies on a new filler material for cable insulation have been conducted. The influence of Silicon dioxide (SiO2) and Polyhydroxybuyrate (PHB) is added to cross linked polyethylene (XLPE) and results were analysed. Comparison is made between the result of measurement and the actual value of the pure specimen. From the results, it is shown that the filler material has improved the dielectric and mechanical properties of the cable insulation. Keywords— Cross Linked polyethylene; Polyhydroxybuyrate; Silicon dioxide; Insulation resistance; AC breakdown Strength; Tensile strength; Elongation; filler. I. INTRODUCTION NANOCOMPOSITE materials have recently emerged as dielectrics and electrical insulation. In particular, much work has been done on nanocomposites from thermo set epoxies. Nanocomposites from thermoplastic polymers such as polyethylene, ethylene vinyl acetate, polypropylene, polyimide, and silicone are also targets of research. Polyethylene (PE) has long been used as extruded cable insulation for HV and EHV cables, primarily as chemically cross-lined polyethylene (XLPE). The work covers materials characterization, real and imaginary permittivity, dc conductivity, space charge formation, dielectric breakdown, and partial discharge resistance. The Test samples were prepared and tests are conducted. The XLPE used for preparation of the nanocomposites was a standard commercial material used for extruded power cables. The improved XLPE samples, based on nano composite formulations with SiO2, were prepared specifically for this study. Several important improvements were exhibited by XLPE with SiO2 nanofiller over XLPE, auguring well for future potential application in the field of extruded HV and EHV cables. The polymer material (XLPE) is basically not ecologically friendly and not bio degradeable.So the sample in which prepared is added with equal quantity of Poly HyroxyBuyrate (PHB) in order to enhance the Environmental properties.

. II. SYNTHESISATION AND

HARACTERIZATION OF NANO MATERIAL

Appropriate quantity of alcohol TEOS and Distilled water is taken and stirred continuously for 30 minutes. After 30 minutes ammonia is added and stirred continuously for 24 hrs. The white solution is

centrifuged at 6000 rpm for 15 minutes and drying is carried out.

The SiO2 is obtained from the above process. The size of the SiO2 is analysed by Scanning Electron Microscopy (SEM). The size is found to be in nano level. The SEM image of the SiO2 is shown in the Figure 1

Figure 1 SEM image of SiO2

It is observed that the average size of the

powder is from 2 to 10 nm.

III. SYNTHESISATION AND HARACTERIZATION OF PHB

Bacterial cell containing the polymer was pelleted

at 1000 rpm for 10 min.Pellet is washed with acetone ad ethanol to remove the unwanted materials .Pellet was resuspended in equal volume of 4 % Sodium hypochlorite and incubated at room temp for 30 min .The whole mixture is again centrifuged and unwanted materials are discarded.PHB containing cell pellet was again washed with acetone and ethanol Polymer granules was dissolved in hot chloroform and again chloroform is filtered. To the filtrate + conc. 10 ml hot H2SO4 will convert the polymer into crotonic acid (brown colored solution).Soln was cooled and absorbance was read at 235 nm against

Analysis On Electrical And Mechanical Properties Of Cable Insulation With NANO Composites

ASAR International Conference, Coimbatore Chapter- 12th May 2013, ISBN: 978-81-927147-4-5

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sulphuric acid blank. By referring the Std curves, PHB produced is determined.

Figure 2 TEM image of PHB

IV. SAMPLE PREPARATION In this work, the XLPE has a density of 0.965 g·cm–3, melting point of 195°C, a tensile strength of 35 MPa and a melt flow index of 25 g/10 min (230°C, 2.16 kg). The XLPE (without filler) was studied in comparison with XLPE formation (containing different concentration of fillers i.e., 2.5%, 5%, and 7.5%). XLPE/Silicon dioxide filler/PHB were melted using a laboratory Two Roll Mill. Mixing of the samples was done at a temperature of 195°C and mixing speed of 30 rpm for 30 minutes. The lumps are obtained from Two roll mill machine after the mixing process. The lumps are kept in compression moulding machine and composite plates with dimensions of 270 * 130* 3mm3 were moulded at a temperature of 160°C and pressure of 135 MPa for 2 hours and followed by cooling for 5 hours. These plates were cut into circular plate with dimensions of 100mm diameter and 3mm thickness. The studied samples are listed in Table 1.

TABLE 1:

FORMULATIONS STUDIED IN THIS PROJECT

Formulation XLPE

(Gram)

Silicon dioxide

(Gram)

PHB

Sample 1 100 0 0 Sample 2 100 5 5

V. LABORATORY STUDIES

This project consists of four parts of experiments, which are Breakdown Voltage test, Insulation Resistance test, Tensile strength test, Elongation test. All the experiments were performed using relevant Standards. AC breakdown test

This method describes a technique for evaluating the ability of an insulating material to resist electrical breakdown perpendicular to the plane of the material when subjected to short term, high voltages at

standard AC power frequency. AC breakdown test is carried to find out the dielectric strength of the sample in the insulating prepared sample. Breakdown test is performed according to the standard (IS-10810-part 45, 1984). At room temperature and pressure voltage applied at the rate voltage. The electrode used for the measurement is (stainless steel) plane-plane configuration. The electrode is 25mm diameter and 75mm diameter used an according to IS 2854. The test set up is immersed in transformer oil to prevent surface flash over. The atmospheric correction factor is considered. Insulation Resistance test

The Insulation Resistance was measured at room temperature by applying 500 V dc voltages to a sample sheet with a circular shape of 100mm diameter and 3mm thickness. The sample is then inserted between plane-plane electrodes. Insulation Resistance test is performed according to the standard (IS-10810-part 43, 1984). The electrode used for the measurement is (stainless steel) plane-plane configuration. The electrode is 25mm diameter and 75mm diameter used an according to IS 2854. Tensile Strength and Elongation test

All uniaxial tensile and static fatigue measurements were carried out on a MTS Elastomer Testing System 810 equipped with a 25 kN force cell. The engineering stresses are calculated using the average of the cross sectional surface areas as measured at three locations in the gauge length. Tensile experiments were carried out at a constant crosshead speed, thus at engineering strain rate. The static fatigue tests were conducted with a constant load, thus at constant engineering stress. All stresses and strains in this paper are engineering values.

Figure 3 Tensile Testing machine and dumb bell sample The samples are prepared according to IS 10810

(part 7) – 1984 and are dumb bell in shape with 75mm length. VI. RESULTS AND DISCUSSION

This study was carried out to investigate the effects of fillers on XLPE cable dielectric Strength and mechanical properties. Experimental samples are basically composed of XLPE compound with fillers. The experiments were performed with the setup described above. A. AC breakdown test

The dielectric breakdown strength was measured at room temperature by applying alternating current

Analysis On Electrical And Mechanical Properties Of Cable Insulation With NANO Composites

ASAR International Conference, Coimbatore Chapter- 12th May 2013, ISBN: 978-81-927147-4-5

24

stress to a sample sheet with a circular shape of 100 * 3 mm2.The sample is then inserted between plane-plane electrodes. Four different specimens sampled from each composite and have been tested. The five test results were averaged and taken as the breakdown voltage. Table 2 shows the breakdown voltage of XLPE, XLPE/Silicon dioxide/PHB. The test samples are identified as S1 and S2 by their filler contents. XLPE cable without fillers was used as a reference, and is called S1. All the samples are of a sheet shape with equal thickness (3mm).

TABLE 2:

RESULT OF BREAKDOWN VOLTAGE TEST Samples S1 S2 Standard IS 10810 (part 45)- 1984

BDV (kV/mm)

13.45 17.67

% increment - 23.88 Results from breakdown tests clearly reveal that

fillers have an important effect on the breakdown voltage of XLPE cable. Compared to the unmodified XLPE cable, samples with fillers enhance the dielectric strength. When 5.0 wt% silicon dioxide particles are added to XLPE, breakdown voltage increases from kV/mm to kV/mm. However, further increase in silicon dioxide particles loading causes the dielectric strength of the compound to decrease. XLPE/silicon dioxide/PHB at 5.0 wt% concentration of silicon dioxide on compound is the best among all due to its high breakdown voltage.

B. Insulation Resistance test

The Insulation Resistance will be measured by Megger meter. Four different specimens sampled from each composite and have been tested. The five test results were averaged and taken as the breakdown voltage. Table 3 shows the breakdown voltage of XLPE, XLPE/Silicon dioxide/PHB. The test samples are identified as S1 and S2 by their filler contents. XLPE cable without fillers was used as a reference, and is called S1. All the samples are of a sheet shape with equal thickness (3mm).

TABLE 3:

RESULT OF INSULATION RESISTANCE TEST

Samples S1 S2 Standard IS 10810 (part 43)- 1984

Equipment Meggermeter MIT52012

Resistance (GΩ)

15.45 37.52

Volume resistivity (GΩ.cm)

252.35 612.82

% increment - 58.82

The XLPE/silicon dioxide/PHB improvement in insulation resistance test compare to unmodified XLPE. When 5.0 wt% silicon dioxide particles are added to XLPE, insulation resistance increases from GΩ to GΩ. However, further increase in silicon dioxide particles loading causes the insulation resistance of the compound to decrease. XLPE/silicon dioxide/PHB composite at 5.0 wt% concentration of silicon dioxide on compound is the best among all due to its high insulation resistance.

C. Tensile Strength test

The Tensile Strength will be measured by Tensile testing machine. Four different specimens sampled from each composite and have been tested. The five test results were averaged and taken as the tensile strength. Table 4 shows the tensile strength of XLPE, XLPE/Silicon dioxide/PHB. The test samples are identified as S1 and S2 by their filler contents. XLPE cable without fillers was used as a reference, and is called S1. All the samples are of a dumb bell shape with equal thickness (3mm).

TABLE 4:

RESULT OF TENSILE STRENGTH TEST Samples S1 S2 Standard IS 10810 (part 7)- 1984

Equipment Tensile testing machine (UTM-G-120B)

Load (N) 100.46 127.16 Tensile Strength (N/mm2)

8.37 10.59

% increment - 20.96 When 5.0 wt% silicon dioxide particles are added

to XLPE, tensile strength increases from 4.18 N/mm2 to 6.83 N/mm2. However, further increase in silicon dioxide particles loading causes the tensile strength of the compound to decrease.

D. Elongation test

The Elongation is measured by Tensile testing machine. Four different specimens sampled from each composite and have been tested. The five test results were averaged and taken as the elongation. Table 5 shows the elongation of XLPE, XLPE/Silicon dioxide/PHB. The test samples are identified as S1 and S2 by their filler contents. XLPE cable without fillers was used as a reference, and is called S1. All the samples are of a dumb bell shape with equal thickness (3mm).

TABLE 5:

RESULT OF ELONGATION TEST Samples S1 S2 Standard IS 10810 (part 7) - 1984

Analysis On Electrical And Mechanical Properties Of Cable Insulation With NANO Composites

ASAR International Conference, Coimbatore Chapter- 12th May 2013, ISBN: 978-81-927147-4-5

25

Equipment Tensile Testing machine (UTM-G-120B)

Elongation (mm) 63.25 78.92

% Elongation 216.25 294.6

% increment - 26.59

When 5.0 wt% silicon dioxide particles are added to XLPE, elongation increases from N/mm2 to N/mm2. However, further increase in silicon dioxide particles loading causes the elongation of the compound to decrease. CONCLUSION The test results show that the addition of silicon dioxide has an impact on the dielectric and mechanical properties. It is concluded that AC breakdown voltage is higher than the normal unmodified XLPE for 5.0 %wt of silicon dioxide. Insulation resistance is higher than the normal unmodified XLPE for 5.0 %wt of silicon dioxide. Tensile strength is % higher than the normal unmodified XLPE for 5.0 %wt of silicon dioxide. Elongation is % higher than the normal unmodified XLPE for 5.0 %wt of silicon dioxide It can be concluded that 5.0% wt silicon dioxide mixed with XLPE is best among all in regards due to increase the dielectric and mechanical properties ACKNOWLEDGMENT

I wish to express my heartfelt thanks to Dr. Somu, Scientific Officer, Department of Electrical, National Test House, Chennai and Dr. Bhuvana, Associate Professor, Department of Plastic Engineering, Central Institute of Plastic Engineering and Technology, Chennai for providing the lab facilities to complete the work. REFERENCE [1] Diater Kind and Hermann Kamer, “High Voltage Insulation

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