Ch.
3
POWER CABLES “1 kV and 3 kV”
Part 1: CONSTRUCTION
1- INTRODUCTION
The cables are the main part of the electrical responsible for translate the power
from pint to others during the network.
In this chapter the construction, testing, losses, dimension and protection of the power
cables of rated voltages of (1 kV and 3 kV), will be introduced.
IEC 60502 and IEC 60228 standards will be used as references for our explaining.
IEC 60502 consists of the following parts, under the general title Power cables with
extruded insulation and their accessories for rated voltages from 1 kV (Um = 1,2
kV) up to 30 kV (U m = 36 kV):
Part 1: Cables for rated voltages of 1 kV (Um = 1,2 kV) and 3 kV (Um =3,6 kV);
Part 2: Cables for rated voltages from 6 kV (Um = 7,2 kV) up to 30 kV (Um = 36 kV);
Part 4: Test requirements on accessories for cables with rated voltages from 6
kV (Um = 7,2 kV) up to 30 kV (Um = 36 kV).
As described above, in this chapter we will use IEC 60502-1, which include the power
cables of rated voltages of (1 kV and 3 kV).
In this part of this chapter the construction and testing of the power cables of rated
voltages of (1 kV and 3 kV), will be introduced.
2- TERMS AND DEFINITIONS
2.1. Definitions of dimensional values (thicknesses, cross-sections, etc.)
2.1.1. Nominal value
Value by which a quantity is designated and which is often used in tables
2.1.2. Approximate value
Value which is neither guaranteed nor checked; it is used, for example, for
the calculation of other dimensional values.
2.1.3. Median value
when several test results have been obtained and ordered in an
increasing (or decreasing) succession, the median value is the middle
value if the number of available values is odd, and the mean of the
two middle values if the number is even
2.2. Definitions concerning the tests
2.2.1. Routine tests
Tests made by the manufacturer on each manufactured length of cable
to check that each Length meets the specified requirements
2.2.2. Sample tests
tests made by the manufacturer on samples of completed cable or
components taken from a completed cable, at a specified frequency,
so as to verify that the finished product meets the specified
requirements
2.2.3. Type tests
tests made before supplying, on a general commercial basis, a type of
cable covered by this standard, in order to demonstrate satisfactory
performance characteristics to meet the intended application.
2.2.4. Electrical tests after installation
Tests made to demonstrate the integrity of the cable and its accessories
as installed
3- VOLTAGE DESIGNATIONS
The rated voltages U0/U (Um ) of the cables considered in this
standard are 0,6/1 (1,2) kV and 1,8/3 (3,6) kV.
NOTE 1 The voltages given above are the correct designations
although in some countries other designations are used, e.g. 1,7/3 kV
or 1,9/3,3 kV instead of 1,8/3 kV.
In the voltage designation of cables U0 /U (Um): according to (IEC 60038).
U0 is the rated power frequency voltage between conductor and earth or
metallic screen for which the cable is designed;
U is the rated power frequency voltage between conductors for which the
cable is designed;
Um is the maximum value of the "highest system voltage'' for which the
equipment may be used
4- Conductors
The conductors shall be either of Class 1 or Class 2 of plain or metal-coated
annealed copper (coated with a thin layer of suitable metal, such as tin or tin alloy) or of
plain aluminium or aluminium alloy, or of Class 5 of plain or metal-coated
copper in accordance with IEC 60228.
The classification of the conductors is:
Class 1: solid conductors.
Class 2: stranded conductors.
Class 5: flexible conductors.
Class 6: flexible conductors which are more flexible than class 5.
The types of insulating compound covered by this standard are listed in Table 3,
together with their abbreviated designations.
The maximum conductor temperatures for different types of insulating compound
covered by this standard are given in Table 2.
Table 3 – Insulating compounds
Abbreviated
Insulating compound
designation
a) Thermoplastic
PVC
Polyvinyl chloride intended for cables with rated voltages U 0 /U ≤ 1,8/3 kV
b) Thermosetting:
Ethylene propylene rubber or similar (EPM or EPDM) EPR
High modulus or hard grade ethylene propylene rubber HEPR
Cross-linked polyethylene
XLPE
Table 4 – Maximum conductor temperatures for different types of insulating
compound
M maximum conductor temperature °C
Short-circuit
Insulating compound Normal operation (5 s maximum
duration)
Polyvinyl chloride (PVC)
70 160
Conductor cross-section ≤300 m m 2
70 140
Conductor cross-section >300 m m 2
Cross-linked polyethylene (XLPE) 90 250
Ethylene propylene rubber (EPR and HEPR) 90 250
The nominal insulation thicknesses are specified in Tables 5 and 6.
The assembly of multicore cables depends on the rated voltage and whether a
metallic layer is applied to each core.
The inner coverings may be extruded or lapped.
For cables with circular cores, except cables with more than five cores, a
lapped inner covering shall be permitted only if the interstices between the
cores are substantially filled.
A suitable binder is permitted before application of an extruded inner
covering.
The materials used for inner coverings and fillers shall be suitable for the
operating temperature of the cable and compatible with the insulating material.
Cables with rated voltage 0,6/1(1,2) kV may have a metallic layer
collectively surrounding the cores.
7- METALLIC SCREEN
The metallic screen shall consist of one or more tapes, or a braid, or a
concentric layer of wires or a combination of wires and tape(s).
It may also be a sheath or, in the case of a collective screen, an armour .
When choosing the material of the screen, special consideration shall be
given to the possibility of corrosion, not only for mechanical safety but also for
electrical safety.
The dimensional, physical and electrical requirements of the metallic screen
shall be determined by national regulations and/or standards.
8- LEAD SHEATH
The sheath shall consist of lead or lead alloy and shall be applied as a
reasonably tight-fitting seamless tube.
9- METALLIC ARMOR
9-1 Types of metallic armour
The armour types covered by this standard are as follows:
a) Flat wire armour;
b) Round wire armour;
c) Double tape armour.
NOTE For cables with rated voltage 0,6/1 (1,2) kV with conductor cross-
sectional areas not exceeding 6 m m 2 , galvanized steel wire braid armour may
be provided by agreement between the manufacturer and the purchaser.
9-2 Materials
Round or flat wires shall be of galvanized steel, copper or tinned
copper, aluminum or aluminum alloy.
Tapes shall be of steel, galvanized steel, aluminium or aluminium alloy.
Steel tapes shall be hot- or cold-rolled of commercial quality.
10- OVER SHEATH
All cables shall have an over sheath.
The over sheath is normally black but a color other than black may be
provided by agreement between the manufacturer and the purchaser,
subject to its suitability for the particular conditions under which the cable is
to be used.
10-1 Material
The over sheath shall consist of a thermoplastic compound (PVC or polyethylene or
halogen free) or an elastomeric compound (polychloroprene, chlorosulfonated
polyethylene or similar polymers).
