Performance Survey of PVC Insulation of LC/Gecamines Electrical Cables Subjected to Ageing and Its Life Span Evaluation

Considering the insulators ageing in a mixture of PVC and dye, set following operating conditions and time to ensure proper operation and perfect safety of industrial installations using insulated conductors. The results showed that the insulation carried out by the L.C main office was a good quality (on thermal aspect), because the resistance of the insulation is so high (i.e. 3940 Mega Ohms under normal conditions). The results showed a lifespan of 50 years at a temperature of 40˚C (close to ambient temperature), plus minus 33 years at a temperature of 70˚C; plus minus 22 years at a temperature of 100˚C and 12 years at a temperature of 160˚C. Furthermore, information on chemical attack, the results showed that PVC cables have poor resistance to sulfuric acid attack (having a pH of 1.5 and a density of 1.84 g/cm 3 ). LC/Gecamines is able to produce locally a good quality of electrical cables.

factory has been annexed to the Congolese mining giant GECAMINES under the name of "Rolling mills and cable factories main office" [1]. Previously, about 95% of companies in RDC used the insulated electrical cables from L.C/Gecamines for their internal installations. The cables are insulating with various types of polymers [2]. The insulation can age; it can suffer from defects due to operating conditions, and at the same time cause invaluable damage at the industry [3].
Therefore, the accurate prediction of the service life and operating conditions of electrical cables is obviously becoming an economic, safety and strategic issue for the industry [4]. However, the life span and operating conditions of electrical cables are mainly relating to the life span of their insulation.
Indeed, the insulating tape is the direct element in contact with the external environment. Therefore, the insulating tape is the first defect element exposed to chemical, thermal (external) and mechanical deterioration [5]. The material used by L.C/Gecamines for the insulation of this external insulating tape is polyvinyl chloride (PVC).
Each electrical wire in a factory must be carefully covered with some type of electrical insulating tape (PVC in the case of this study). The wire itself is usually made of copper or aluminum, which are known to be good conductors of electrical power. The insulation must be opposite from the conductor; meaning, it must resist to electrical power and keep the latter in a path along with a conductor [6]. Insulated material can age, it can fail due to operating conditions, and it can cause inestimable damage to the plant.
The study gap is to evaluate the performance and life span of L.C/Gecamines cables subjected to a thermal force ageing to characterize their resistance to chemical attacks.

The Sample and LC/Gecamines Presentation
The L.C/Gecamines main office is a production entity of Gecamines Company in the Democratic Republic of Congo, engaged in the processing of non-ferrous metals ( Figure 1 & Figure 2). The insulated wire produced by L.C/Gecamines main office, was mainly composed of 99.73% copper and some other impurities at acceptable levels ( Table 1). The wire-bars received by the headquarters from Shituru mining plant, had a deformation of ±2%. These wire bars were recycled in a FRITZ furnace at 400˚C -450˚C for 3 hours of heating time, half an hour of holding and 18 hours of cooling. This operation resulted in new characteristic as shown in

Studies Materials
BALTEAU apparatus were use in this study; it is a generator of medium voltage from zero to 10 kV, used for tests of dielectric rigidity of the insulator ( Figure   3). The objective within was to determine the lifetime of cables based on the resistance of the insulation. A good insulation was defined as the insulation resistance that has a great value or equal to 1/100 of the applied voltage [7].
This lifetime is a function of the insulator's resistance. The insulator must resist to the current, and maintain the latest in its trajectory along with the conductor.

Methods and Experimental Setup
In order to determine the resistance of the insulation, five samples (for each temperature) of 60 cm length and 9.075 mm 2 cross-section were prepared and stripped at both ends; the central part of the sample was attach in the water bath ( Figure 3(b)). The two ends were not in contact with the water (setup shown in Figure 4). The phase of the device was connect to the first stripped end of the   was sent through the cable (the time depends on the test to be performed).
During the study, the applied method was to determine the leakage current of the insulating tape than based on Ohm's law, deduced the resistance of the insulating tape: In order to evaluate the chemical attacks resistance, the used of a round bottom flask of 11, a principal solution, distilled water for dilution, a volumetric pipette, sulfuric acid, two beakers and a stopwatch. After the samples and the sulfuric acid solution's preparation, these samples were immerse in an acid solution for 48 hours and then dried after 24 hours in an oven at 150˚C until a constant mass was obtain.

Results Presentation on the Total Resistance of the Cable
The table shows 3940.88 Mega Ohms characterizes the resistance of PVC insulation. However, it should be noted that there is no such thing as perfect insulation (i.e., no insulation has infinite resistance); from that, a certain quantity of electricity always flows along or through the insulation to the outside environment.
A good insulation essentially means a relatively high resistance to current. In order to describe an insulating material, a good insulation also means "the ability to maintain a high resistance" [8].
Having a look at the results obtained in Table 4, a confirmation come out that the isolation performed at L.C/Gecamines main office is good quality. Furthermore, if measured at regular time intervals, it is possible to monitor it degradation's trends.  According to this theory, the lifetime seems to be long because the main way of PVC insulation deterioration at this temperature consists in the evaporation of the plasticizer, the deshychloration is so low and even negligible. The Brebu's work [9], who studied waste medium voltage cables (6 -10 kV) after 18 years of operation, concludes that the PVC's deshycloration is very low under service conditions. Indeed, according Hishler [8], it would take at least 2 billion years to have a release of 1% by mass of HCl at 40˚C. clearly, this estimate has no physical significance since the material itself will not survive that many years, but it does confirm that deshychloration of PVC is a negligible phenomenon at low, near ambient temperatures. If the temperature is at 70˚C, the only mode of plasticizer loss was evaporation;

Estimated Lifetime of Insulating Tape in PVC
Graphic 2. Progress of the strength of PVC as a test time's function at a temperature of 70˚C.
however, at 100˚C, this loss is largely due to evaporation of the plasticizer but also to a slight deshychloration. The Hishler's work [8] shows a very low release off HCl below 105˚C (close to 100˚C) (Graphic 4).

Resistance to Acid Attacks
Each insulating tape's presence constituents particularly affects the acid resistance value of the cables.

Conclusions
The present work is divided in two parts, the evaluation of the performance and showed that the insulation carried out by the L.C/Gecamines main office is a great quality because the insulation resistances are high (i.e. 3940 Mega Ohms Table 6. Results of the chemical attack test.

Designation
Front weight (g) Mass taken after (g) Losses (g) Weight gain 6.0918 5.8448 0.247 World Journal of Engineering and Technology under normal conditions). The results showed a lifetime of more than 50 years at a temperature of 40˚C (close to an ambient temperature), ± 33 years at a temperature of 70˚C, 22 years at a temperature of 100˚C and ± 12 years at a temperature of 160˚C. For chemical attacks, the results showed that PVC cables have a poor resistance to sulfuric acid attack (having a pH of 1.5 and a density of 1.84 g/cm 3 ). These results allow L.C/Gecamines's customers to realize that is possible to order insulated electrical cables that can work in such extreme temperature conditions but also on short scale into higher acidic environment.