Ethylene Propylene Rubber Insulation Research Articles

Resistance evaluation of electrical insulating polymer materials used in flexible cables to operational impact

The article presents the test results of polymer material properties taking into account the possibility of their application for flexible cables insulation. The main types of cable constructions and their operation features are considered. Existing test determination methods of insulation resistance to thermal, mechanical, electrical and environmental conditions are analyzed. Requirements for laboratory equipment and test conditions are given. Evaluation criteria of test results are noted. Experimental evaluation was carried out for change degree in the properties of the main types of electrical insulation materials used currently during the flexible cable production: polyvinyl chloride compound (PVC), rubber, ethylene propylene rubber (EPR), thermoplastic elastomer (TPE), fluoropolymer. Tests were carried out under the influence of high and low temperatures, aggressive environments, ozone, mechanical loads. The main processes that determine the changes in electrophysical, physical and mechanical properties of the studied materials are described. Resistance of EPR, TPE and fluoropolymer insulation to a wide range of temperatures, mechanical loads, diesel fuel and transformer oil are shown. An increased resistance of EPR to ozone was also noted. Rubber and PVC compound did not pass the tests under the influence of low and high temperatures, showed "poor" resistance to aggressive environments, but passed the mechanical stress tests. Recommendations on tests and application of polymer insulation taking into account the specifics of flexible cables working are presented.

Influence of surface discharge on the deterioration characteristics of ethylene‐propylene rubber cable insulation under alternating current high voltage

To investigate partial discharge-induced deterioration characteristics of ethylene-propylene rubber (EPR) cable insulation under repeated alternating current (AC) voltage on high-speed trains, an experimental platform with a column-plate EPR insulation model is established. The surface condition and breakdown voltage of insulation samples after discharge treatment are observed and measured. In addition, a fitting formula to evaluate the deterioration extent of EPR samples is proposed. The results show that under repeated discharge pretreatments, the volume resistivity increases first and decreases afterwards when discharge magnitude is low. When partial discharge (PD) intensity increases to 100 pC, the volume and surface resistivity decrease monotonously, and the decreasing rate is positively correlated with PD intensity. During PD pre-treatment, a white circle appears near the electrode and turns to pale yellow with PD intensity. For PD pretreatments of 50 and 100 pC, withstand voltage of EPR insulation increase first and decrease afterwards, and the downward trend is slow. For PD pre-treatments of 200 and 400 pC, the withstand voltage decreases significantly with the degradation time. The fitting formula model shows that under the action of a strong electric field, the relationship between the reliability of EPR insulation samples, the probability and rate of molecular chain breakage, and the intensity of discharge activity is not linear.

Experimental study on ageing characteristics of electric locomotive ethylene propylene rubber cable under mechanical–thermal combined action

The train-mounted ethylene propylene rubber (EPR) cables of electric locomotive are partly restricted by the body structure and spatial layout and are in a combined environment of strong mechanical bending and thermal ageing. The degradation characteristics of the insulation layer have not yet received sufficient attention. In order to study the ageing characteristics of EPR cables of electric locomotive under the combined action of machine and thermal, this paper designs a bending–thermal combined ageing test platform for cables with a temperature of 135°C, bending diameter of 393.52 mm, 590.28 mm and unbending cables, and tests after ageing. The product has been tested by infrared spectroscopy, scanning electron microscopy, elongation at break and broadband dielectric spectroscopy. The research results show that the bending outer part of the train-mounted EPR cable is a pain point. Under the combined action of bending and thermal, whether it is microstructure or macro performance, the degradation rate and degree of the bending of outer insulation layer are greater than the value under a single thermal ageing condition. Mechanical bending has an accelerating effect on the ageing of the EPR insulation layer. The research results can provide a reference for the ageing characteristics of the train-mounted EPR cable under the bending–thermal synergy and the evaluation of operating state of the train-mounted EPR cable under bending–thermal operating conditions.

Influences of low temperature on internal gas-filled cavity discharges in EPR cable termination and its feature factors analysis

Ethylene–propylene rubber (EPR) cable is the most commonly used type in high-speed railway. Several flashover accidents take place in cable termination in an extremely cold environment. In this study, EPR cable terminations were tested in a simulated low-temperature system with varied applied voltages. The results showed that the differences in elastic modulus and free space volume between EPR insulation and stress control tube (SCT) in a frigid environment would lead to structural defects between them. Damages on the EPR insulation occurred in the form of flashover point when the ambient temperature declined to −30°C and below, with the growth rate of discharge and resulting extent of damage across the EPR/SCT interface being non-linearly related to ambient temperature. Besides, the partial discharge (PD) initial voltage and PD extinction voltage under low-temperature conditions reduced by >40% compared with those at 20°C. The flashover probability of EPR terminations increased significantly, and the shape characteristics of PD patterns have also changed obviously at low temperatures. It can be verified that under the high-voltage and low-temperature conditions, the EPR/SCT interface is prone to organisational mismatch, which will lead to the PD phenomenon and seriously affect the stable operation of EPR cable terminations.

Measurement and Diagnosis of PD Characteristics of Industrial Cable Terminations in Extreme Cold Environment

In the alpine region, there are many flashover failures of ethylene-propylene rubber (EPR) cable terminations due to cavity discharges in China high-speed railways (CHRs). The cable termination with cavity defects is used as test samples and a low-temperature PD test system is set up to study the characteristics of partial discharge (PD) of cavity defects in cable termination in those regions. Influences of the different temperatures on internal discharge in EPR insulation at −40°C and 20 °C have been analyzed. When the applied temperature dropped to −40°C, the PD initiation voltage and extinction voltage decreased by 31% and 28%, respectively, and the discharge pulse appeared at both positive and negative half-cycles. The results showed that, at 20 °C, the discharge was mainly caused by the internal discharge of the gas-filled cavity. Apart from the internal discharge of the gas-filled cavity, a marked trace of surface discharge was also detected at −40°C. Besides, the characteristics of PD development at −40°C are closely related to the discharge phase distribution and the asymmetry of the spectrum. The research can further reveal the development and evolution of PD of the gas-filled cavity and provides a basis for judging the severity of termination at low temperature.

Aging Life Evaluation of Coal Mining Flexible EPR Cables Under Multi-Stresses

As important power cables for the mining mobile equipment, such as mining shearers, ethylene propylene rubber (EPR) cables often suffer from the combining effect of various stresses on site. In order to evaluate the aging state of EPR insulation, the paper carried out the multi-stress accelerated aging test on the insulation of coal mining flexible EPR cables. The infrared spectrum, elongation at break and polarization and depolarization current of cable insulation samples were measured. The insulation state of EPR cable was evaluated by using the aging factor obtained from isothermal relaxation current. Based on the failure standard of 50% elongation at break, the life formula of EPR insulation was deduced. The experimental and analytical results show that the tiny air gap was torn to the larger air gap under the mechanical stress, which leads to the increase of oxygen infiltration and promotes the thermo-oxygen reaction. The fracture energy of EPR decreases, and mechanical aging is accelerated. Aging factor and elongation at break can indicates the deterioration degree of EPR insulation. Based on the least square method and Arrhenius equation, the service life of the insulation of coal mining flexible EPR cables is deduced.

Mechanism elucidation of degradation dynamics of ethylene propylene rubber cable insulations sampled from nuclear power containment using additional aging

Ethylene propylene rubber insulation under operation for 16 years in boiling water reactor containments was subjected to additional thermal aging at 110°C. After 70 days of aging, the mechanical property of the insulation was decreased such that the limit guaranteeing durability against design-basis events was breached. This degradation rate is three times slower than that predicted on the basis of an accelerated aging test with control samples. Infrared spectroscopic analysis revealed suppression in the formation of carbonyl products in the service-used cables. According to the gel fraction measurement, cross-linking is the dominant reaction in such service cables. The unique slow degradation dynamics observed in service cables could be attributed to such oxidation control and the cross-linking reaction. The present study also conducts nuclear magnetic resonance analysis to elucidate the cross-linking point in the main chain.

Influence of temperature on dielectric properties of EPR and partial discharge behavior of spherical cavity in EPR insulation

Ethylene propylene rubber (EPR) with outstanding high temperature performance has been widely used as cable insulation. To understand the influence of temperature on the feature of EPR, a series of study has been conducted including the dielectric measurements, the breakdown voltage and PD behavior of cavities. In the experiments, the dependency of permittivity, conductivity and electric modulus on frequency and temperature has been investigated firstly. Then, the experiments of breakdown voltage have been performed under the applied voltage in the temperature range from 25 °C to 200 °C. Finally, PD behavior caused by artificial spherical cavities in EPR has been examined at the temperature of 25 °C, 100 °C and 150 °C, respectively. It can be concluded by the experiments that the relaxation processes of EPR similar to other polymer materials can be featured by a rapid decrease of the real part of complex permittivity and a slow decrease of dissipation factor with increasing frequency at higher temperature. The dielectric dispersion phenomena can be observed on the spectroscope of the electric modulus which follows the Havriliak/Negami model. The phase resolved PD distribution, such as ϕ-q-n plots and ϕ-n plots, caused by cavities can be characterized as the multi-stem-like distribution. The repetition rate, the average discharge power and the average discharge current have shown a more strong dependency on the temperature.

EPR의 가속 열화에 의한 기계적 특성 및 통계적 평가

Department of Environmental Health, Seonam University, Namwon 590-711, Korea(Received July 9, 2015; Revised July 23, 2015; Accepted July 24, 2015)Abstract: In this paper, EPR (ethylene propylene rubber) insulation material was accelerated degradation test at 121, 136, 151, and experiment the typical EAB (elongation at break) at mechanical characteristics analysis. It is shown that the failure-time at the point of 50% of the initial value of Elongation rate to obtain the activation energy. The failure-time was shown each 5,219 hr, 3,165 hr, and 668 hr at three temperatures. In order to derive the activation energy, Arrhenius methodology was applied. Also, we got the Arrhenius plot from three accelerated temperatures. The activation energy values got 0.98 eV from EAB test. The experimental data were evaluated for estimating the probability density, and the suitable distribution by using statistical program MINITAB. It is shown that EAB data by the acceleration thermal degradation is most suitable for the Weibull distribution.Keywords: Nuclear cable, EPR, Arrhenius equation, Activation energy, EAB, Statistical evaluation)*+ 케이블의 절연체 및 자켓은 XLPE (cross-linking polyethylene), EPR (ethylene proplyene rubber), CR (chloroprene rubber)고무, CSP (chloro sulphonated polyethylene) 등이 사용되고 있으며, 원자력발전소에 사용되는 케이블의 경우에는 고온, 고압, 방사선에 견디

Mechanical aging trend in ethylene propylene rubber-insulated safety cables sampled from bwr nuclear power containment

Statistical analysis has been performed on variously aged ethylene propylene rubber insulation on cables removed from boiling water reactor-type containment. Temperature and dose rate conditions of such cables are not identical. Therefore, elongation at break data observed for such insulation are converted to each equivalent period under 60 °C, 10 mGy/h condition. The aging trend is found to be approximately slower by half than that expected from accelerated aging test results. Furthermore, this aging trend is used as a reference to fit to each elongation value, and the fitted curve is extrapolated to find the end of service life, which is defined as 70 % of absolute elongation. Lifetimes estimated from this method and from predictions by the accelerated aging test are compared on an Arrhenius plot. It is suggested that the latter lifetime estimation is shorter than actual. The temperature dependence also suggests a difference in a basic chemical reaction under the two aging conditions, which results in apparent differences in activation energies and pre-exponential factors.

Partial discharges of cavities in ethylene propylene rubber insulation

The aim of this paper is to investigate the characteristics of partial discharge (PD) within dielectric-bounded and electrode-bounded cavities which are embedded in Ethylene Propylene Rubber (EPR) by using plane to plane electrode. The theoretical analysis is carried on the electric field strength and PD inception voltage of cylindrical and ellipsoidal cavities in different dimensions. The samples with the different dimensions of artificial spherical cavities in EPR are made and the PD characteristics in the cavities, such as PD number, amplitude and phase, are measured by professional instrument in laboratory. It has been found by the experiments that the symmetric PD distribution changes from “rabbit-like” to “turtle-like” shape with the time of applied voltage. With the increase of applied voltage on the samples, the PD inception phase becomes prior to the zero crossing of positive and negative half-cycle. Meanwhile, PD pulse repetition rate has an increase trend with increasing the experimental voltage and the amplitude of PDs occurred in dielectric-bounded cavities changes from a higher value to normal during a short time. However, no obvious amplitude change of PDs occurred in electrode-bounded cavities has been observed in the experiment. As a result, internal PDs occurred in cavities is one of the prime reasons resulted in the degradation and corrosion of EPR.

A new method to estimate the average dielectric constants of aged power cables

A new method to estimate the average dielectric constants of cable sections that have undergone aging is proposed. By comparing the experimental Joint Time-Frequency Domain Reflectometry waveform signatures from a new and an aged cable of the same type, it is demonstrated that the change in the average dielectric constant of the insulation material due to aging can be estimated. For example, for a cable containing Cross-Linked Polyethylene insulation, accelerated aging tests based on the modified Arrhenius equation that simulate 120 years of aging at 50 °C operating temperature show that the dielectric constant of the insulation decreases by more than 34.5%. The same tests performed on another cable containing Ethylene-Propylene Rubber insulation show that the average dielectric constant of the insulation decreases by 10.4%. The efficacy of the method is further demonstrated by estimating the increase in the average dielectric constant of a wedge section of a cable that contained water intrusion.

Application of Low Frequency Dielectric Spectroscopy to Estimate lifetime of Low-Voltage EPR Insulation

This paper deals with the application of integral values of dielectric spectroscopy as the characteristic values from 10Hz to 1Hz for estimating the lifetime of low-voltage ethylene propylene rubber( EPR) insulation cables aging in the lab. The elongation-at-break and the dielectric dissipation factor (tanδ) were measured to study the characteristics of curve and to analyze sensitive measurement range. Based on the failure criterion of elongation-at-break, the correlation between the mechanical and dissipation curve was investigated and the effectiveness among three ways to assume values of dielectric dissipation factor was compared. Meanwhile, a time multiplicative shift factor was found with the same characteristics value at different aging temperatures and a prediction equation after selected reference temperature was obtained. Combined with integral equation of the deterioration tendency under reference temperature, a life model of dielectric dissipation factor integral for insulation material was derived. Results showed that testing parameters on integral value of tanδ had a contrary tendency with elongation-at-break and reflected the degradation trend in sensitive range within 10Hz~1Hz. Compared life model calculation results with measurements of cable in field, the measurement error was 3.33%. It had been found that this method could effectively evaluate the aging lifetime of low-voltage cable EPR insulation materials.

Correlation between mechanical and electrical properties for assessing the degradation of ethylene propylene rubber cables used in nuclear power plants

The correlation among the indenter modulus, the elongation-at-break, and the breakdown-voltage strength for the ethylene propylene rubber (EPR) cables subjected to long-term thermal aging and high-temperature water submerging conditions were investigated in this work. The mechanical and electrical limits of EPR insulation material were evaluated by using an indenter modulus, with non-destructive advantage, to monitor the cable condition and to assess its remaining life. Results show that it is plausible to use indenter modulus to monitor the EPR cables for the condition approaching the end of cable service life. Testing parameters on indenter modulus, including indenter diameter, penetration speed, and penetration depth, were studied for monitoring cable degradation condition. Finally, this paper discusses the cable acceptance criteria under thermal and moisture-related aging environments. Results show that the breakdown-voltage strength is a better acceptance criterion for assessing the cable aging condition in a wet environment. While, if the cable is located in a high temperature environment, the elongation-at-break is a better criterion.

Lifetime predictions of EPR materials using the Wear-out approach

The Wear-out approach for lifetime prediction, based on cumulative damage concepts, is applied to several ethylene propylene rubber (EPR) cable insulation materials. EPR materials typically follow “induction-time” behavior in which their material properties change very slowly until just before failure, precluding the use of such time-dependent properties to predict failure. In the Wear-out approach, a material that has been aged at its ambient aging temperature T a or at a low accelerated aging temperature is subsequently aged at a higher “Wear-out” temperature T w in order to cause the material to reach its “failure” condition. In the simplest case, which involves the same chemical processes underlying degradation at T a and T w, a linear relationship is predicted between the time spent at T a and the time required at T w to complete the degradation. Data consistent with this expectation are presented for one of the EPR insulation materials. When the degradation chemistry at the two temperatures is different, a linear relationship between the time spent at T a and the time required at T w to complete the degradation is not generally expected. Even so, the Wear-out results for a second EPR material, which has evidence of changing chemistry, are reasonably linear and therefore useful from a predictive point-of-view. The Wear-out approach can therefore be used to transform non-predictive time-dependent material property results into predictive lifetime estimates. As a final example, the Wear-out approach is applied to an EPR insulation that had been aged in a nuclear power plant environment (∼51 °C) for times up to 23 years to show its likely viability for the hundreds of years predicted at this aging temperature from accelerated aging tests on EPR insulation materials.

Development of non-filled EPR insulation system for power lead of 66 kV-class superconducting fault current limiter

Development of ethylene-propylene rubber (EPR) insulation system has been advanced for a compact power lead of 66 kV-class high temperature superconducting fault current limiter (SCFCL). It is well known that insulation layers of superconducting cables are molded by extruding EPR containing inorganic filler. The power leads are not as long as the superconducting cables, making it difficult to mold their insulation layers by extrusion. When molding EPR by heat treatment, voids tend to remain in the insulation layer because of the low viscosity of filler-containing EPR. Partial discharge will occur and insulation deteriorates if voids exist in the insulation layer. Fluidity of EPR without filler (non-filled) was experimentally investigated to be used for insulating power leads. It was found that the viscosity of non-filled EPR is sufficiently low. It was also found that non-filled EPR has excellent crack resistance. An insulation model was easily constructed with simple dies. No voids were found in the insulation layer of this model, and no cracks occurred by thermal cycling between 333 K and 77 K. Consequently, it was confirmed that non-filled EPR is a suitable material for insulating power leads.

Ac treeing of ethylene-propylene rubber in cryogenic temperature region

The authors have proved that ethylene-propylene rubber (EPR) is suitable for the solid electrical insulating material of superconducting and cryoresistive cables due to its excellent mechanical and good electrical properties. It is imperative to study the treeing resistivity of EPR in view of long-term reliability as a cable insulator. The objectives of this paper are to establish an ac treeing test method of opaque EPR samples with fillers and to examine the treeing resistivity of EPR at both liquid-nitrogen and room temperatures and the effect of fillers on treeing resistivity. It was found that EPR has enough resistance to ac treeing at liquid-nitrogen temperature and that fillers improve ac treeing resistivity slightly. High reliability of EPR insulation is expected during long-term operation at cryogenic temperature. © 1998 Scripta Technica, Electr Eng Jpn, 124(3): 1–9, 1998

極低温領域におけるエチレンプロピレンゴムの交流トリーイング特性

The authors have proved that ethylene-propylene rubber (EPR) is suitable for the solid electrical insulating material of superconducting and cryoresistive cables due to its excellent mechanical and good electrical properties. It is imperative to study the treeing resistivity of EPR in view of long-term reliability as a cable insulator. The objectives of this paper are to establish an ac treeing test method of opaque EPR samples with fillers and to examine the treeing resistivity of EPR at both liquid-nitrogen and room temperatures and the effect of fillers on treeing resistivity. It was found that EPR has enough resistance to ac treeing at liquid-nitrogen temperature and that fillers improve ac treeing resistivity slightly. High reliability of EPR insulation is expected during long-term operation at cryogenic temperature.

Development and tests of extruded ethylenepropylene-rubber-insulated superconducting cable

The simultaneous application of the design voltage (20 kVrms) and current (2 kArms) to ethylenepropylene-rubber (EPR)-insulated superconducting cable, cooled by liquid helium, was successfully carried out. The superconductor was a niobium layer clad on a copper pipe. The EPR insulation was extruded simultaneously with semiconducting electrostatic shielding layers. A specific advantage of this cable design is the complete exclusion of the cryogenic helium from the electrical insulation structure.

Oxidation induction time correlations with radiation dose and antioxidant concentration in EPR and XLPE polymers

AbstractOxidation induction time (OIT), as measured by differential scanning calorimetry, is useful in assessing the extent of degradation in polymeric materials. Values of OIT for typical EPR and XLPE polymer insulation materials used for electric cable insulation in nuclear power plants were measured as a function of both radiation dose and antioxidant concentration after accelerated aging. Irradiations were performed at the University of Virginia Cobalt Irradiation Facility. OIT was found to decrease exponentially with increasing radiation dose and with decreasing antioxidant concentration for both ethylene‐propylene rubber (EPR) and cross‐linked polyethylene (XLPE) insulations. It was determined experimentally that, when polymers are subjected to a constant radiation dose rate, antioxidant concentration decreases linearly with time, and it was shown that this variation is consistent with theoretical autoxidation kinetics. © 1993 John Wiley & Sons, Inc.