MEDIUM VOLTAGE CABLES
(MV CABLES) IN ELECTRICAL CONSTRUCTION
The contractor shall supply, install, test and commission
the 13.8 KV cable network as shown and indicated on the contract documents.
Conductor sizes shall be metric as shown, conductor sizes with cross sectional
areas smaller than specified will not be accepted. The cable installation shall
include all trench work, sleeves, ducts, and all necessary fixings and cable
terminations at both ends of the cable. The contractor shall supply and install
cable marker posts to indicate the route of all underground cables. Markers
shall be provided at every bend along the route and at sites of crossing roads
or pipe lines.
The medium voltage cable shall be standard circular compact
copper conductors, XLPE insulated, copper tape screened, assembled together
with non-hygroscopic polypropylene fillers, covered with tapped bedding
unarmoured and PVC sheathed. Cables shall comply with IEC 502.
APPLICABLE STANDARDS
The design of cables for use in the 13.8 KV network shall be
based on IEC specification 502. Contractor may propose cable to other
International Standards for the review of the Architect/Engineer and approved
by the Client.
For each lot of cable the Contractor shall supply a
certificate of original and test issued by the manufacturer stating its
original, date of manufacture and standards to which it complies. In the
absence of such documents, the Architect / Engineer reserves the right to
require tests, at the Contractor’s expense, to be performed by an official
laboratory on samples taken from lots of cables delivered on the site.
BASIS FOR MV POWER
CABLE SELECTION
The contractor shall check cable ratings indicated on
drawings against final equipment ratings and system fault levels when known.
Any required change in cross sectional area of the cable proposed shall be
brought to the attention of the Engineer in charge. Products for the use of
this work shall be obtained from Approved Cable Company.
CONSTRUCTION OF MV
POWER CABLE
Medium voltage cables shall be armoured, 15 KV XLPE
insulated copper conductor cables having the following characteristics:
1. Conductor: Plain circular compacted copper conductor to
IEC 228 Cl. 2.
2. Conductor screen: Extruded semi conductive compound.
3. Insulation: XLPE (cross linked polyethylene extruded and cross linked by silanc curing process rated 90 deg. C.
4. Insulation screen (non-metallic part): Graphite layer covered with a lapping tape or extruded semi conductive material.
5. Insulation screen (metallic part): Copper tapes 0.10 mm thickness.
6. Bedding: Tapped bedding.
7. Armour: Galvanized steel tapes applied helically over the PVC bedding.
8. Outer sheath: PVC Type ST2 To IEC 502 Color Red.
2. Conductor screen: Extruded semi conductive compound.
3. Insulation: XLPE (cross linked polyethylene extruded and cross linked by silanc curing process rated 90 deg. C.
4. Insulation screen (non-metallic part): Graphite layer covered with a lapping tape or extruded semi conductive material.
5. Insulation screen (metallic part): Copper tapes 0.10 mm thickness.
6. Bedding: Tapped bedding.
7. Armour: Galvanized steel tapes applied helically over the PVC bedding.
8. Outer sheath: PVC Type ST2 To IEC 502 Color Red.
MEDIUM VOLTAGE POWER CABLE
INSTALLATION
The contractor shall be required to carry out necessary
field surveys and acquaint himself with the routing of all other service lines.
Cables shall be laid directly on ground on 10 cm minimum
soft sand, and ground will be back filled properly avoiding any aggregate with
sharp edges for damaging the cable insulation. Contractor shall provide 5 cm
thick cement tiles above the back fill then HT marker for safety.
The cable ladder shall be bounded to ground at both ends.
All cables shall be marked with their respective cable
numbers all along their routes at intervals not greater than 2.5 meters.
Spliced and joints on MV cables are not permitted.
Radius of cable bends shall be greater than 12 times the
outside diameter of the cable.
FIELD TESTS OF MV
CABLE
All high voltage cables furnished under contract shall be
tested by the contractor in the presence of Engineer to determine if properly
installed and provide satisfactory performance. Contractor shall provide all
test equipment required.
Cable testing shall be a minimum of but not limited to the
following:
1. Every cable shall be tested prior to its connection to
site voltage, in the following manner.
2. The contractor shall test all sub main cables using DC
voltage injection equipment and digital volt meter. The test for cables shall
follow the following procedure.
2.1 Insulation resistance test.
2.2 Apply test voltage for 2 minutes on each of the
following :
- Phase
to phase.
- Phase
to neutral.
- All
conductors to earth.
All conductors not under test shall be bonded to earth. The
Contractor shall record the leakage current at the time of all tests.
2.3 Apply a reduced AC voltage at 60 Hz and record the
charging current.
3. All final connections and small wiring shall be tested
using a 1000 V megger and each reading tabulated and submitted to the
supervising officer.
4. The test voltage shall be Dc 2 E + 2 KV where “E” equals
the line (phase to phase) voltage that the cable will see in normal operation.
It will be acceptable to test LV cable while connected to their source, if the
source may be readily isolated.
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