Covered conductors consist of a conductor insulated by a covering made of insulating material(s) as protection against accidental contacts with other covered conductors and with grounded parts such as tree branches etc. In comparison with insulated conductors, this covering has reduced thickness, but is sufficient to withstand the phase-to-earth voltage temporarily.
Construction of MVCC
Conductor: Longitudinally water tight stranded all aluminium alloy (AAAC) or aluminium conductor steel reinforced (ACSR).
A (conductor screen): Water swellable semi-conducting tape (if required) and extruded semi-conducting compound.
B (inner insulation): XLPE
C (outer insulation): UV protected and anti-tracking black coloured XLPE or HDPE.
Anti tracking properties
Anti-tracking property is must for MVCC outer XLPE/HDPE. As per the experience of several international utilities, in the absence of anti-tracking, XLPE or HDPE, MVCC fails within a short time period of 5-6 months. Anti-tracking jacketing has been specially designed to meet the outdoor conditions and performance requirements of 13.8 KV to 34.5 KV distribution networks. The material has an excellent resistance to arc, corrosion inhibitor, fungicide activity, oil resistance, and weather conditions like humidity, pollution, presence of salt in atmosphere etc. There is a special test method for carrying out the tests for the anti-tracking in SS EN 50397-1.
Applicable Standards
SS EN 50397-1, BS EN 50182, IS 398-2, IS 398-4, IEC 61089
Salient features of MVCC technology
Rare interruptions on transient faults (contact of tree branches or creepers etc.) that contribute the majority of total faults occurred in overhead distribution lines.
Less power shut downs for clearing of the lane from growing trees. Branches or trees can be cut and moved away under live working conditions.
No faults due to momentary clashing of phase conductors during wind and stormy conditions.
Reduced tower related cost due to reduced phase to phase conductor distance.
Ideal and safer solution for installations over river, lake, railway and road crossings, slums, congested residential areas and in polluted areas
Accessories used by MVCC
Moreover lighting protection earthing and arc protection accessories are available.
Easy installation
Covered conductors can be installed in an easy and fast manner. Normal pole to pole spacing can be between 50-70 metres; standard poles of bare conductor can be used for covered conductors as the weight of covered conductors is only about 10-12 per cent higher than bare conductor due to insulation. For fast installation even existing poles of bare conductors can be used without changing the cross arms and other fitting with covered conductor and its accessories.
Benefits of MVCC
- No interruptions by contact of tree branches.
- No faults with short duration touching of phase conductors during wind conditions.
- Phase to phase conductor distance can be reduced (reduce the tower costs).
- Ideal and safer solution for installations for river, lake, railway, road crossings and in populated areas.
- Can protect big birds like peacocks and flamingos etc. Ideal for installations in forest areas and in bird sanctuaries.
- Covered conductors are a cheaper alternative to underground cable and also to ABC cables, especially in difficult terrain and in densely populated areas.
- Lines near to areas where the public visit are not so dangerous because of accidental touching.
- Overcomes costly right of way issues and line can be commissioned faster.
Conclusions
Covered conductors are the best economical solutions where ever the safety of human and Wildlife is been challenged or compromised by bare conductors. It gives maintenance free overhead line reliability. Service calls will drastically reduced which means an uninterrupted power supply adding more revenues to the utility. It is a Safe, Economical, environmental friendly, reliable solution for Utility to protect the Wildlife from been electrocuted.
