High Voltage Distribution System (HVDS)
- HVDS systems having lines right upto consumer’s small single phase transformers are run at a medium voltage.
- Fully insulated metallic screened MV ABC systems have been mainly used in India for HVDS systems.
- MV ABC eliminates the constraints of availability of tree clearances, bush fire risk areas with overhanging trees, highly congested localities, and vulnerability to power thefts.
A High Voltage Distribution System with MV ABC requires voltage stress- relief terminations at every joint, termination and tap.
- These cables are shielded, screened and tested to confine full operation voltage.
- These cables are having different layers of insulation, voltage stress relief , anti tracking and metallic shield provide a designated path for fault and charging current to flow in case of insulation failure.
Problems while erecting these lines stem from
A) Making Tees at discontinuities.
B) Difficulty in access to conductor for testing and earthing maintenance.
C) Operations, Switching, Earthing practice significantly different from the ones followed for bare conductor mains and in fact closer to the ones followed by underground system requiring extensive training for installation and maintenance personnel.
- Single phase & Neutral (continuous neutral from sub-station)
- Two phase with two wires (rigidly earthed natural system)
- Three phase small rating transformer with 3 phase HV system
- Unauthorized hooking of loads will be prevented.
- Reduced KVA capacity results negligible voltage drop on LV lines and hence improves the voltage profile
- A capacitive load (Power factor > 0.95) of single phase motors contributes lesser energy loss.
- Reduces breaker trip at the substation.
- Its initial capital cost is higher but overall cost & benefit of the system is economical.
- Increases efficiency of the electric supply system.
Domestic: Punjab, Andhra Pradesh, Assam, Kerala, Rajasthan.....
International: USA, UK, Australia, Germany, Sweden, Brazil, Ireland....
Fully insulated metallic screened ABC system has found limited usage on account of prohibitive cost.
It has mostly found applications where medium voltage lines have to be taken through confined spaces near congested houses and buildings sites or obstructions. In such cases public safety and “safe to touch” system is the over riding need.