The cable is able to carry permissible steady-state current. This current, which is given in the cable specification, depends on such factors as ambient temperature, cable construction and routing. This leads to a temperature rise in steady-state operation.
The cable is capable of withstanding a faulty current which may occur, without deterioration. It sustains a conductor temperature rise appreciably higher than that occurring under continuous load. The temperature rise depends essentially on the type of cable insulation used. Effects of shortcircuits between cable ends are not taken into account in sizing cables (it is assumed that the cable is simply replaced).
The cable does not produce an excessive voltage drop between the power source and the load, under steady-state conditions or during motor start up. The cable cross-section is selected so that the voltage at the motor terminals is 0.8 Un when bus voltage is at the lower limit of the normal range.
NOTE: In practice and depending on the intended service, each cable may be sized on the basis of only one of the above criteria.
Ambient temperature is taken into account as follows:
as a general rule, an ambient temperature of 30°C is adopted for those cables supplying equipment which can be de-energised in the event of a general loss of air-conditioning which, sooner or later, leads to plant shutdown;
a higher temperature may be adopted for cables supplying equipment which is necessary in the event of a general loss of ventilation and, in particular, those cables which are necessary for air-conditioning equipment;
however, overheating of cables is acceptable for short periods since this has only a minor effect on service life.
A5. Separation rules between cables of different electrical tvoes
The purpose of the separation between cables of different electrical types is to protect the various electrical circuits from electromagnetic interference.
The rules described below concern all cables.
Excerpt from 'Design and Construction Rules for Electrical Equipment of Nuclear Islands (RCC-E)' published by ’Association franqaise pour les regies de conception et de construction de materials des chaudidres 6lectro-nucl6aires, (AFCEN)’, chapter D2242 (1993).
Excerpt from (RCC-E), chapter D 7400 (1993).
The following electrical types can be distinguished:
medium voltage power;
low voltage power;
utility (telephone, intercom, public address system, lighting, etc.);
control;
instrument.
The separation criterion taken into account is the voltage level and the nature of the signals.
The routings are normally overhead; the following methods may be used.
5.1 Overhead routings ■
In the same raceway, the cable trays are assigned in the following way:
cables of different electrical types are routed on different cable trays or risers;
on horizontal or diagonal raceways, the cable trays assigned to power cables are located in the upper part and the order of assignment of the cable trays complies with figure 1.
the control and low voltage power cables may run on the same tray in secondary raceways (see sub-clause A7.2);
instrument cables run through enclosed troughs when a power cable (MV or LV) passes less than 1 m away;
instrument cables transmitting signals output by nuclear instrumentation system detectors, or signals of comparable level, pass through enclosed troughs. These instruments cables can also transmit the HV specific to the detector power supply.
The minimum distances to be respected between the cable trays carrying cables of different electrical types are (see figure 2):
d1 > 0.15m, when the cable trays are parallel and stacked;
d2 > 0.1 Om, when the cable trays cross in separate planes;
d3 > 0.10m, when the cable trays are parallel on the same horizontal plane.
These distances presuppose that the instrument cables pass through enclosed troughs.SECTION В: UNARMOURED CABLES WITH COPPER CONDUCTORS
Replace pages 5-B-3, 5-R-15 and 5-B-16 by the following:'BLANK PAGE'
External marking (Provisional!
The external surface of all cables shall be legibly marked as follows:
Cables without metallic covering
R
or or
G10M1-0.6/1 kV - 1 x cross-section ENCRG10M2-0.6/1 kV - 1 x cross-section ENC
RG1 OOM 1-0.6/1 kV - number of conductors x cross-section ENC or
RG100M2-0.6/1 kV - number of conductors x cross-section ENC or
FG100M1-0.6/1 kV - number of conductors x cross-section ENC or
FG100M2-0.6/1 kV - number of conductors x cross-section ENC
Screened cables
RG10H1M1-0.6/1 kV - 1 x cross-section ENC or
RG10H1 M2-0.6/1 kV - 1 x cross-section ENC or
RG100H1 M1-0.6/1 kV - number of conductors x cross-section ENC or
RG100H1 M2-0.6/1 kV - number of conductors x cross-section ENC or FG1 OOH 1 M1-0.6/1 kV - number of conductors x cross-section ENC or FG100H1M2-0.6/1 kV - number of conductors x cross-section ENC
Furthermore, a metre mark, at 1m intervals, shall also be applied.
The legend shall be along one or more lines and in the latter the lines shall be approximately equally spaced around the circumference.
When embossing or indenting is used, the letters and figures shall consist of upright block characters.
In the legend, the maximum size of the character shall be 13mm and the minimum size 15% of the specified overall diameter or 3mm, whichever is greater.
In case of printing, the print height shall be 15% of the specified overall diameter as a minimum. The numbers shall be printed in a colour which contrasts with the oversheath colour.
Compliance shall be checked by visual examination and measurement.
2.3 Additional test requirements
Sampling for sample tests
The number of finished lengths to be checked is stated according to ISO 2859-1974. General inspection level I and single sampling plan for reduced inspection, with AQL - 2.5%, shall be adopted to define sample size.
If a cable length (or a cable sample or a test piece taken from it) does not fulfil even only one out of the test requirements, the cable length is classified as defective, and it is rejected.
When the AOL value is not met all delivered cable lengths shall be tested and the defective ones are rejected.Measurements of cable dimensions
When the overall dimension of the cable is checked in accordance with sub-clause 2.1.3.1 of HD 605, the mean overall dimension shall comply with the values specified in Tables 4 to 6. When the ovality of the cable is checked in accordance with sub-clause 2.1.3.2 of HD 605, the difference between the maximum and minimum value of the diameter shall not exceed 15% of the overall diameters specified in Tables 4 to 6.
Checking number of conductor wires (class 2 conductors)
Determine by inspection the number of conductor wires of one core of each length of cable selected for the test. ■
Bend test on complete cable
The bend test shall be carried out at ambient temperature in accordance with sub-clause 2.4.1.1. of HD 605, immediately after conditioning in a straight arrangement for at least 1 h at (0 ± 3)°C.
The mandrel diameter shall be 16 (D + d) ± 5%, D and d being the measured overall diameter and the conductor diameter, respectively.
After the bend test, the U-bent cable shall be immersed in water at ambient temperature, leaving above water a length of sample adequate for the test.
A voltage of 4 kV a.c. or 12 kV d.c. shall be applied for 10 min on succession between each conductor and all other conductors connected together and to water.
The test level shall be attained be gradually increasing the voltage.
No breakdown shall occur.
After the voltage test, a piece of cable of about 18 D in length (D being the measured overall diameter in the middle of the sample) shall be stripped carefully and the various components shall be visually examined.
Neither breaking of conductor nor cracks of insulation or oversheath are allowed.
Checking tinning of copper wires
When tested in accordance with sub-clause 2.5.3 of HD 605, the wires shall not show black spots unremovable by rubbing when examined with normal vision (black spots placed at less than 10mm from wire end are not considered). One stained wire out of seven is tolerated.
Measurement of density of insulation
During type tests the density of a sample of insulation, taken from on end of one core of the cable length, shall be determined using the test method given in HD 505.1.3, clause 8, and the result shall be recorded.
For sample tests the density of the insulation shall be determined as above. The value obtained shall not differ by more than +0.04 g/cm3 from that determined in the type tests.
Determination of hardness of elastomeric insulation and sheath
During type test, the hardness of samples of insulation and oversheath, taken from one end of one core of the cable length, shall be determined in accordance with sub-clause 2.2.5 of HD 605 and the result shall be recorded
.Table 3 - Schedule of tests
|
1 |
2 |
3 |
4 |
5 |
|
Ref. |
Test |
Category |
Test method |
Requirement given |
|
No |
of test |
described in |
in clause (') |
|
|
1 1.1 |
Electrical tests Conductor resistance |
T & S |
HD 383 |
3.3.1 |
|
1.2 |
Metallic screen resistance |
T & S |
HD 60Б 3.1.1 |
4.3.4 |
|
1.3 |
Voltage tests: a) Core |
T |
HD 606 3.2.2.2 |
2.3.9 |
|
|
b) Complete cable |
T & R |
HD 60Б 3.2.1 |
2.3.8 |
|
1.4 |
Insulation resistance tests: a) Core |
T & s |
HD 60Б 3.3.1 |
2.3.10 |
|
|
b} Complete cable |
T & s |
HD 605 3.3.3 |
2.3.10 |
|
2 2.1 |
Constructional and dimensional characteristics Conductor: a) material & construction |
T & s |
Visual examination |
3.3.1 |
|
|
b) diameter of wires |
T & s |
HD 605 2.1.4.1 |
3.3.1 |
|
|
(class 5 conductors) c) number of wires |
T & s |
2.3.3 |
3.3.1 |
|
|
(class 2 conductors) d) tinning of wires |
T & s |
HD 605 2.5.3 |
2.3.5 |
|
2.2 |
Insulation: a) Application |
т & s |
Visual examination |
Part 1, 5.5.2 |
|
|
b) Thickness |
T & s |
HD 605 2.1.1 |
3.3.2 & Part 1, |
|
2.3 |
Core identification |
T & s |
Visual examination |
5.2.3 2.1 & Part 1,4 |
|
2.4 |
Metallic screen |
T & s |
& measurement Visual examination |
4.3.4 |
|
2.Б |
Oversheath a) Application |
T & s |
& measurement Visual examination |
3.3.4 & Part 1, |
|
|
b) Thickness |
T & s |
HD 605 2.1.2 |
5.7.2 3.3.4 & Part 1, |
|
2.6 |
Cable markings |
T & s |
Visual examination |
5.7.3 2.2 & Part 1, 3 |
|
2.7 |
Cable dimensions: a) Overall dimension |
T & s |
& measurement HD 605 2.1.3.1 |
2.3.2 |
|
|
b) Ovality |
т & s |
HD 605 2.1.3.2 |
2.3.2 |
|
3 3.1 |
Mechanical & physical tests Insulation: a) Mechanical properties in the |
T & s |
Table 1 |
3.3.2 |
|
|
state as delivered. b) Mechanical properties after |
T |
Table 1 |
3.3.2 |
|
|
ageing in air oven c) Ozone resistance |
T |
Table 1 |
3.3.2 |
|
|
d) Hot set test |
T & s |
Table 1 |
3.3.2 |
|
|
e) Water absorption (gravimetric) |
T |
Table 1 |
3.3.2 |
|
|
f) Density |
T & s |
HD 505.1.3, 8 |
2.3.6 |
|
|
g) Hardness |
T & s |
HD 605 2.2.5 |
2.3.7 |
|
|
h) Thermal life |
T |
HD 605 5.1.3 |
2.3.17 |
|
|
i) Themorgravimetric test |
T & s |
Amend to HD 605 |
2.3.19 |
|
|
|
|
2.5.7 |
|
(*I Clause numbers refer to this section unless stated otherwise.
Table 3 (continued)
|
1 |
2 |
3 |
4 |
6 |
|
Ref. |
Test |
Category |
Test method |
Requirement given |
|
No |
of test |
described in |
in clause {') |
|
|
3.2 |
Inner covering: |
|
Amend to HD 605 |
2.3.19 |
|
3.3 |
Thermogravimetric test Oversheath: a) Mechanical properties in the |
T & S T & S |
2.5.7 Table 2 |
3.3.4 |
|
|
state as delivered b) Mechanical properties after |
T |
Table 2 |
3.3.4 |
|
|
ageing in the air oven c) Mechanical properties after |
T |
Table 2 |
3.3.4 |
|
|
ageing in mineral oil d) Heat shock test |
T & s |
Table 2 |
3.3.4 |
|
|
e) Pressure test at high temp. |
T |
Table 2 |
3.3.4 |
|
|
f) Hot set |
T & s |
Table 2 |
3.3.4 |
|
|
g) Bending test at low temp. |
T |
Table 2 |
3.3.4 |
|
|
h) Elongation test at low temp. |
T |
Table 2 |
3.3.4 |
|
|
i) Impact test at low temp. |
T |
Table 2 |
3.3.4 |
|
|
j) Water absorption (gravimetric) |
T |
Table 2 |
3.3.4 |
|
|
k) Hardness |
T & s |
HD 605 2.2.6 |
2.3.7 |
|
|
1) Thermogravimetric test |
T & s |
Amend to HD 605 |
2.3.19 |
|
4 |
Compatibility test on complete cable |
T & s |
2.5.7 HD 505.1.2, 8.1.4 |
Tables 1 & 2 |
|
Б |
Bend test on complete cable |
T |
HD 605 2.4.1.1 |
2.3.4 |
|
6 |
Thermal endurance on complete cable |
T |
HD 605 5.1.2 |
2.3.18 |
|
7 7.1 |
Tests related to fire conditions: Insulation a) Oxygen index |
T & s |
HD 405.3 (Арр B) |
2.3.15 |
|
|
b) Temperature index |
T & s |
HD 605, 4.5 |
2.3.16 |
|
|
c) Corrosive gas emission |
T |
IEC 754-1 |
2.3.13 |
|
7.2 |
Inner covering: a) Oxygen index |
T & s |
HD 405.3 (Арр B) |
2.3.15 |
|
|
b) Temperature index |
T& s |
HD 605, 4.5 |
2.3.16 |
|
|
c) Corrosive gas emission |
T |
IEC 754-1 |
2.3.13 |
|
7.3 |
r Oversheath: a) Oxygen index |
T & s |
HD 405.3 (Арр B) |
2.3.15 |
|
|
b) Temperature index |
T & s |
HD 605, 4.5 |
2.3.16 |
|
|
c) Corrosive gas emission |
T |
IEC 754-1 |
2.3.13 |
