Thursday, February 3, 2011

POWER CABLE INSULATION M/CS.

1.3 Machines:
There are six machines used for insulation: BM 80, BM 100, BM 120, BM 150, BM160 and SAM P BM 160. The number appeared in the name of the machine is related to the diameter of the screw of each machine. Section 3 of this report gives a wide overview of those machines and their specifications. Any machine is able to put insulation, but the BM150 and BM160 is mainly used for bedding and sheathing.
2. PROCESSES
2.1. Introduction
Three different processes are carried out in the insulation section
• insulation,
• bedding,
• Sheathing.
2.2. Insulation process
Two materials are used for the insulation process: Polyvinyl chloride (PVC), and cross-linked polyethylene (XLPE).
The main differences are summarized as follows
• PVC has a maximum operating temperature of 70 C, and for the XLPE is 90 C.
• XLPE, P.V.C are used as insulation for LV cables, while XLPE is used just for MV and HV. However, the incoming material of XLPE used in MV and HV is more pure than in LV, so it is stronger, but at the same time more expensive.



• PCV and XLPE are color less by nature. The color is put according to the customer needs and the Standards; the basic colors are: Red, yellow, blue, and black. The ratio of color is 2 % for PVC and between 0.5 % and 1 % for XLPE. The name of the material used for coloring is "Master batch".
2.3. Bedding process
This process is done right after the assembly process. It is an operation done between stages, before armoring, and before sheathing, if any of those two operations are carried out.
PVC is used as a material, but it is not the same kind of PVC used for insulation. Now, it is recycled PVC of black color. It has not as good electrical characteristics as that one used for insulation, however now there is no need of that, because the objective of the bed layer of the cable is just to be a separator and to protect the insulated cores from the effect of the armoring or screening.
2.4. Sheathing process
The sheath is the outer jacket of a cable used as a cover, just for protection.
This process uses the same extrusion method as that one used for insulation and bedding.
Materials used here are coming in colors, not natural or color less as for insulation.
PVC is used for LV and MV, and its color is according to the Standards (black, red, yellow, etc). The sheathing depends on the customer (depending on its use) and it can be divided as: Flame retardant, flame and termite retardant, acids retardant, ultraviolet retardant, L.S.O.H, underground water resistant.
PE comes in black color, and it is divided into three types, the first two used for MV, LDPE (Low Density PE) and MDPE (Medium Density PE), and the third one used for HV, HDPE (High density PE).

Friday, January 28, 2011

power cable insulation section



1. Insulation section:
1.1 introductions:
- It is a process, for protecting the conductor from the contact with the other conductors in the cable (multi core cables), or due to any external hazards (single core cables).
- The insulation dielectric withstands the voltage applied on the cable during the testing or operating conditions.
- The insulation done by Extrusion process.
- The types of cables in this section of insulation:
1- Low voltage cables:
* Solids.
* stranded (round, compact, sector).
1.2 Materials:
Two types of insulation materials:
1- P.V.C Polyvinyl chloride:
Polyvinyl chloride (PVC) is a flexible or rigid material that is chemically non reactive. PVC has a broad range of applications, from high volume construction related products to simple electric wire insulation and coatings. Rigid PVC is easily machined, heat formed, welded, and even solvent cemented. PVC can also be machined using standard metal working tools and finished to close tolerances and finishes without great difficulty. PVC accepts paint and performs well under most silk-screening processes. PVC resins are normally mixed with other additives such as impact modifiers, fillers and stabilizers, providing hundreds of PVC based materials with a variety of engineering properties.




There are three broad Classifications for rigid PVC compounds: Type I, Type II, and CPVC. Type II varies from Type I due to greater impact values, but lower chemical resistance. CPVC has greater high temperature resistance. These materials are considered "un plasticized", because they are less flexible than the plasticized formulations. Type I, II and CPVC are normally available in rod, sheet, slab, pipe, tubular bar, fittings and valves. "Plasticized" PVC is available in sheet, film, fittings, flexible tubing, and pipe.
P.V.C Polyvinyl chloride (for cables):
- It is a compound material.
- Most used materials for the insulation of L.V cables.
- Max operating temperature: 70 degree.
- It is a flexible and flam retardant material.
- Profile temperature during process up to 175 degree.
- It is a thermoplastic material.
- Always provides in granules.
2- PE: Polyethylene:
-Polyethylene resin is useful for applications that require chemical resistance, little or no moisture absorption and flexibility. Its use is limited to temperature applications below 200 degrees Fahrenheit, and it has the ability to carry light loads for a long period. Polyethylene products include machined valves and fittings for fluid handling systems, tanks and pumps and industrial products that require a thermoplastic with low or high density, linear low density or ultra low density, tie-layer resins or adhesive resins. Polyethylene satisfies demands for reduced weight, increased strength, fast processing and lower costs. Polyethylene meets the needs of many tough applications.
-Three types: H.D.P.E, M.D.P.E, L.D.P.E




- H.D.P.E is mostly used in the insulation of communication , data and irrigation cables , due to its dielectric is constant and very low value so it decreases the capacitance of the pairs inside the cable , the surface is very smooth so they can not absorb the water , withstand high operating temperature.
-H.D.P.E also mostly used in the jacketing of M.V , H.V and EX H.V cables with black color to resist the ultraviolet sun beams .
- The profile temperature of the P.E during insulation process is up to 200 degree.
3 -XLPE (cross linked polyethylene):
Since cross linked polyethylene was introduced for the insulation of power cables in the 1960's, XLPE cables have became the industrial standard for voltages from 1kv to 150kv. Excellent technical properties, advantageous production economy and ease of installation and operation are the primary reasons for this development.
Step wise improvements in quality of insulation and semi conductive compounds, as well as cable production processes, have enabled stresses in the extruded dielectric to rise to a level which permits the safe design of cables for voltages up to 500kv.
- The X.L.P.E has high mechanical and thermal properties, operating temperature up to 90 degree,
It consists of two materials the main material which is L.D.P.E and a catalyst, to have the full mechanical and thermal properties of the insulation material the cross liking (curing) must be achieved between the P.E and the catalyst.







Cross linking (Curing) process:
1- mixing the L.D.P.E resin with 5 % catalyst and 1-2% master batch , and make the insulation process to produce an insulated cable , till now there is no X.linking or curing between the P.E resin and the catalyst so the insulation will fail in the Hot set test ( the test that insure that curing is done ) , we must make a heat treatment for the insulated cores , by putting the insulated cores in a heated steam Room named sauna in a temperature 90 degree for 8 hours , after that apply hot set test to ensure that the X. linking is occurs between the P.E resin and the catalyst and the insulated cores gain its thermal and mechanical properties of X.L.P.E material .
2- Current technology;
Now it is not need to use a Sauna or make heat treatment to the insulated cable with X.L.P.E
Due to the latest technology the catalyst is supplied to make self curing with the P.E resin during the insulation process or after 2 hrs, 24 hrs, 2 days according to the specification of the supplied catalyst.
Hot set test:
/ L original x100 Elongation = (L final –L original)



Types of curing technology






3- Benefits of cross linking:
- increased temperature performance.
- increased tensile strength.
- reduced deformation under load.
- improved chemical resistance.
- increase abrasion resistance.
4 –L.S.O.H (low smoke 0 halogen):
- It is a thermo set material, special type of X.L.P.E with free of smoke.
- Also supplied with resin and catalyst.
- used for insulation or sheathing for a special proposes, if the customer needs no smoking from the cable during the fire.

5- EPR: Ethylene Propylene Rubber.
- It is a very flexible material.
- used for insulation and sheathing for some mechanical proposes.