A covered conductor tender that simply says “MVCC, 11 kV, 100 sq mm” leaves too much open. Two bids against that line can differ in conductor material, covering construction, accessory standard and test evidence, and the evaluation committee has no fair basis for comparing them. The checklist below sets out what a utility specification should state, in the order a bidder needs it.
1. System and route data
State the nominal system voltage and the highest system voltage, the method of neutral earthing, the design fault level and its duration, and the ambient conditions on the route. Say what kind of route it is: forest or wildlife corridor, coastal belt, industrial area, road or rail crossing. The route decides how much weight the tender should put on tracking resistance, UV stability and arc protection.
2. Conductor
Specify the conductor material and size rather than leaving it to the bidder. Covered conductors are made on AAAC, ACSR, ACSS and AL59 ACS cores, and each behaves differently in sag, tension and corrosion. Ask for a longitudinally water-tight conductor, so that water entering at a connector cannot travel along the strands. Where the feeder is also short of capacity, ask bidders to state the maximum continuous operating temperature and the current rating at that temperature for the offered conductor.
3. Covering
Require the covering construction to be declared layer by layer. A three-layer design consists of a semiconducting screen, an inner insulating layer and an outer layer that is UV-stabilised and track-resistant, with the layers co-extruded and bonded. State the minimum covering thickness required by the governing standard for the voltage class, and require the outer layer to be tested for tracking resistance.
4. Standards to name
| Scope | Standard |
|---|---|
| Covered conductors for overhead lines | EN 50397-1 (SS-EN 50397-1) |
| Accessories for covered conductor lines | EN 50397-2 |
| Stranded overhead conductors (core) | BS EN 50182, IEC 61089 |
| ACSR core, Indian standard | IS 398 Part 2 |
| Aluminium alloy (AAAC) core, Indian standard | IS 398 Part 4 |
Name the edition the tender is evaluated against. A bidder quoting an older edition should say so in the deviation schedule.
5. Test evidence
Ask for type test reports from a recognised independent laboratory, with the laboratory, report number and date on each. In India, CPRI and ERDA are the usual references. Define the routine tests to be carried out on every drum and the acceptance tests to be witnessed by the utility’s inspector, and state the sampling plan. The difference between these three kinds of test is set out in the guide to routine, sample and type tests.
6. Mechanical design
Give the ruling span, the maximum span and the pole type, and ask for sag-tension tables at the maximum operating temperature and at the design wind and temperature cases. If the covered conductor is to go on an existing bare line, say so, and ask the bidder to confirm that the offered conductor suits the existing poles, cross-arms and insulators.
7. Accessories
List the accessories to be supplied with the conductor, all to EN 50397-2: suspension clamps, anchoring or dead-end clamps, insulation piercing connectors for covered-to-covered, bare-to-covered and tap joints, and pre-insulated junction sleeves. Buying conductor and accessories from separate sources is a common cause of fit and performance problems, so ask the bidder to confirm compatibility in writing.
8. Line protection
Covered conductor needs protection against lightning and power-arc damage that a bare line does not. The specification should call for arc protection devices and surge arresters, state where they are to be fitted, and make them part of the line design rather than an optional extra. Installation practice is covered in the MVCC accessories and installation guide.
9. Documentation and supply
Require guaranteed technical particulars, cross-section drawings, drum lengths and tolerances, drum marking and the sequential length marking on the covering. Ask for installation instructions and a list of recommended stringing equipment with the bid.
APAR covered conductors are manufactured to SS-EN 50397-1, BS EN 50182, IS 398-2, IS 398-4 and IEC 61089, at 11, 22, 33, 66, 110 and 132 kV, and type tested at CPRI Bengaluru and ERDA Vadodara. Construction and standards are on the covered conductor product page, and route suitability is covered in the MVCC selection guide.