CABLE FITTING BOXES AND GLANDS
Cable Accessories Fitting Boxes & Glands for Medium and High Voltage Underground Cable Project
Focal point of this article is limited on requirement of cable fitting boxes & glands for high voltage and medium voltage underground power transmission cable line project from technology and engineering point of view. Employer’s requirement to service provider of 132kV and 33kV underground power transmission underground XLPE insulated copper cable line should follow conditions stated below as a part of the contract.
Electrical equipment should be fitted with all necessary cable boxes and glands which should be complete with all required fittings. Boxes should be of adequate proportions to accommodate all cable fittings, including stress cones or other means of cable insulation grading, and designed in such a manner that they can be opened for inspection where appropriate without disturbing the gland plate of incoming cable.
Cable entry seals should provide protection against a wide range of hazards like gas, smoke, dust, fire, vibration and electromagnetic interference. The system should tested and certified by recognized authority. Glands for termination of cables to outdoor equipment or indoor areas liable to water spray; hosing or flooding should incorporate provision for sealing against ingress of moisture or dust, and should comply with the requirements of BS 6121 for sealing.
Removable Gasket for Gland and Cable EnclosureFeature of the Cable Enclosure:
- High temperature silicon gasket fitted as standard (improved temperature range –50 °C to +140 °C;
- Maximized glanding area for cable entries;
- Captive hinge facility;
- Improved drainage facility providing an effective water path and assists in the overall ingress protection IP66 / IP67;
- Increased flexibility terminal mounting;
- Internal and External Earth Studs are equipped with a sealing mechanism and are keyed to prevent rotation ;
- Label holder;
- Integrated locking clasp for enhanced on site security.
Removable gasketted steel gland plates should be provided for multi-core cables and side supported enclosures with provision for both fitting on floor or roof as possible while allowing adequate space for manipulation of the cable and glands. Mounting lugs should be pre-fitted with secured as vibration and shock tested in operation. Gland plates for marshalling boxes should be in the form of removable gasketted steel plate, forming bottom part of the box.
A high temperature silicone gasket should provide that enhanced product performance in extreme temperature conditions (–50°C to +140°C). Must meet the IP-Ingress Protection performance and ensures that the gasket is not compromised in use. No ingress path or IP failure in internal or external earth stud must ensure.
Cable Marking in Boxes
The terminals for 3 phase cables should be clearly marked in boxes with the phase colour- Red, Yellow, Blue or approved designations to enable the cables are terminated in the correct sequence.
Filling and venting plugs where required, should be positioned so as to avoid the possibility of air being trapped internally and adequate arrangements should be made for expansion of compound etc. There should be no possibility of oil entering the cable box from an associated oil filled compartment. Cable sealing ends should be arranged to project at least 25mm above the gland plate to avoid moisture collecting in the crutch.
Any chamber which is to be compound filled should be clean and dry and at such a temperature before filling the compound should not solidify during filling process. Filling orifices should be sufficiently large to permit easy and rapid filling.
Cable Box and Gland Approved Standard
All cable boxes should be designed to withstand the high voltage d.c. cable tests prescribed in Standard BS 6346, BS 6480 and IEC 55 as appropriate.
Cable boxes for paper-insulated cables should be complete with universal tapered brass glands and insulated from the box in an approved manner and including an island layer for testing purposes.
Even single core cables are used, particularly for currents in excess of 500 A, adequate steps must be taken to minimize the effects of eddy currents in the gland and bushing-mounted plate.
Cable glands for extruded solid dielectric insulated cables (PVC, EPR, and XLPE) should be of the compression type and as specified in BS 6121. All glands should be used on MICC cables.
Glands for armored or screened cables above 240sqmm should be provided with an integral heavy duty earthing lug capable of carrying the full earth fault current for a period not less than 1 second without deterioration.
Cable Box Design compliances
Cable boxes for the termination of elastomeric cables up in 33 kV nominal service voltages should be designed and dimensioned to provide adequate insulation in air for cables. Clearance and creep age distances should be adequate to withstand the specified alternating current voltages and impulse voltages for service under the prevailing site conditions. The performance is to be met without the use of insulating ‘boots’ shrouds or any other material fitted over or between the cable terminations apart from permanently fitted barriers forming part of the switchgear or cable box.
Means should be provided for preventing accumulation of dirt, dust, moisture, vermin or insects such as to maintain the anticipated life of the equipment. The Service provider should ascertain the means by which elastomeric cables are to be terminated and should provide such information or instructions as necessary to any other service provider or sub-service provider to ensure compliance with this Item.
The cable crutch within a cable box or equipment panel should be protected by the use of a heat-shrink plastic ‘udder’ places over the conductors and crutch.