OUTDOOR CABLE TERMINATIONS
DESCRIPTION OF OUTDOOR HEAT SHRINK CABLE TERMINATIONS
Outdoor cable terminations are complete devices for accession of power cables to overhead power lines. They consist of heat shrink anti-tracking components, cable lugs, mastics, and added components. Termination can be installed at electric supports, power line poles, cable lines.
Outdoor cable terminations are applied for 1-core, 3-core, 4-core, 5-core cables with different type of insulation with round or sector core design, and for armored or unarmored cables or cables with or without screen.
Outdoor cable termination is used in the conditions of rain, snow, salt fog, a thunderstorm discharge, at sharp fluctuations of ambient temperature.
Anti-tracking red tubes and heat shrink cable sheds installed on them are mandatory components of outdoor cable termination.
Tracking is a phenomenon that occurs due to the action of surface discharges on the wet surface of the insulation (rain, salt fog, wet dust). The result is the formation of carbon transmission tracks and the complete destruction of the insulation of cable cores in cable termination.
Tracking in cable termination begins to appear at voltage from 3 kV with increase in voltage. Without the use of anti-tracking components, the service period of the cable terminations is significantly reduced. Tracking resistance of materials is achieved by introducing into the polymer certain materials and oxides of metals, characteristic red color, which extinguish the spark and prevent the appearance of carbon on the insulation surface. Such materials cannot be gray or black because carbon is added to the polymer for this purpose, anti-tracking additives must be prevented.
The use of heat shrink sheds with combination of insulating anti-tracking red tubes additionally affects the stability of the termination, which increases the service period of the termination. Installing heat shrink sheds on each cable core in the termination leads to rupture or significant lengthening of the leakage currents during rain. This prevents the destruction of the insulating surface. Heat shrink sheds form zones on the surface of external insulation of cable cores in termination, which are subject to much less pollution and moisture than the rest of the termination. This reduces the probability of conductive paths or reduces their length. World experience in the design of outdoor termination shows that it is not possible to get rid of tracking in the final external termination due to heat shrink sheds.
Polymer heat shrink sheds and anti-tracking red tubes perform different functions separately, so effective prevention of tracking is possible only if these components are combined.
Main resource indicators of cable outdoor termination are by ZKA, Raychem, Radpol, Cellpack, Ensto, Sicame, 3M, ПЗЭМИ, КВТ, CABELNA ARMATURE LLC:
- strength of external insulation of cable cores in termination due to anti-tracking components;
- exclusion of factors of arc overlap of isolation and influence of the resulted discharges;
- reduction or elimination of factors of sliding discharges;
- reduction or elimination of factors of leakage current formation or its increase in places of insulation of cable;
- exclusion of occurrence of continuous tracking tracks or erosion in places of isolation of a cable in damp conditions;
- elimination of the risk of breakdown of the termination due to the uniform distribution of electric field lines on the cable cut;
- resistance to icing, UV rays, lightning discharges.
CHARACTERISTICS OF OUTDOOR CABLE TERMINATIONS
Outdoor cable termination can be installed at cable with different technical characteristics which one should consider when choosing a termination:
- voltage at cable network: 0,4 kV; 1 kV; 3 kV; 6 kV; 10 kV;
- number of cable cores: 1; 3; 4; 5;
- type of dielectric cable insulation: polymeric (PVC) insulation; plastic insulation;
- mass-impregnated paper insulation, rubber insulating;
- availability of armored or unarmored or screen.
For easy installation all components in cable terminations, CABELNA ARMATURE LLC is technologically agreed on the method of installation and geometric dimensions.
Materials, resistant to temperature, change, which significantly reduces the risk of damage to the cable burner during installation the termination.
Outdoor cable termination is made in the form of a set of details which on the technical characteristics corresponded to cable voltage and cable construction.
The work and function of the system depends on the quality of components of cable outdoor termination.
Outdoor cable termination for unarmored polymeric cables up to 1 kV: 3PKNTP 1, 4PKNTP 1, 5PKNTP 1;
Outdoor cable termination for armored polymeric cables up to 1 kV: 3PKNTPb 1, 4PKNTPb 1, 5PKNTPb 1;
Outdoor cable termination for the mass-impregnated paper cable up to 1 kV: 3KNTP 1, 4KNTP 1;
Outdoor cable termination for the mass-impregnated paper cable up to 10 kV: 3KNTP 10;
Outdoor cable termination for plastic insulated cables up to 10 kV: 1PKNT 10, 3PKNTP 10
THE MAIN STAGES OF PROTECTION OF CABLE INSULATION TO THE POINT OF CONNECTION OF OVERHEAD POWER CABLE LINES
Insulation of outdoor cable termination is provided by a set of insulating heat shrink tubes are supplied with glue.
Double insulation of cores is applied for termination up to 10 kV to cables with mass-impregnated paper insulation:
- primary insulation of cable cores, insulating oil barrier tubes, restores cables core insulation, provides resistance to mechanical damage and the chemical effect of composition for impregnation of the phase insulation of the cable.
- external insulation of the core, thick-walled anti-tracking tube, is resistant to condensation, erosion, tracking, temperature changes and mechanical impact along the entire length of the cable (for termination up to 1 kV is used only external insulation).
Heat shrink sheds set is included in two heat shrink sheds for each cable core for prevent tracking.
Insulation tube for lug and tube to seal the cable sheets are characterized by high electrical strength.
Cable breakout boot allows to carry out repeated regasification without risk of damage of the termination. Cable breakout boot does not crack at branching of cores and does not form microcracks. Together with the mastic it forms monolithic connection.
Electric field strength equalization, sealing the connection that eliminates the formation of gas cavities, provides:
- black filling mastic for sealing the ground unit , and moisture and water resistance of the termination;
- oil barrier resin, with electric field equalization to wind the root, divides the cable. Installed inside the termination, ensures no voids and smoothest electric field equalization which increases the service period of the termination.
The installation of the mechanical lugs with 2-shear heads bolts on each cable core ensures the mechanical electrical strength of the contact connection (mechanical lugs does not sag on the thread during the exploitation due to the high technical characteristics of aluminum alloys in the EU countries). Mechanical lugs with shear heads 2 bolts on a copper or aluminum cable cores, have a high degree of corrosion protection.
Earthing set installation for armored cable:
The ground of earth braid is fixed with a pressure spring made of stainless-steel complete roll spring and contact band. It does not interfere with finding a damaged cable. The unsoldered grounding system is used by ZKA, Raychem, Radpol, Cellpack, Ensto, Sicame, 3M, ПЗЭМИ, КВТ, CABELNA ARMATURE LLC.
Full recovery of the damaged screen:
Restoration of the damaged screen, which is carried out by a metal cover, is done by aluminum foil. This ensures reliable operation of cable joints for high voltage cables and can be an additional factor in equalizing the field strength.
The protection of details during repair work is provided by additional components.