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GB/T 12706.3-2020 PDF in English


GB/T 12706.3-2020 (GB/T12706.3-2020, GBT 12706.3-2020, GBT12706.3-2020)
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GB/T 12706.3-2020English585 Add to Cart 0-9 seconds. Auto-delivery. Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um=1.2 kV) up to 35 kV (Um=40.5 kV) -- Part 3: Cables for rated voltages of 35 kV (Um=40.5 kV) Valid

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GB/T 12706.3-2020: PDF in English (GBT 12706.3-2020)

GB/T 12706.3-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 29.060.20
K 13
Replacing GB/T 12706.3-2008
Power cables with extruded insulation and their accessories
for rated voltages from 1 kV (Um = 1.2 kV) up to 35 kV (Um
= 40.5 kV) - Part 3: Cables for rated voltages of 35 kV (Um =
40.5 kV)
ISSUED ON: MARCH 31, 2020
IMPLEMENTED ON: OCTOBER 01, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 4
1 Scope ... 7
2 Normative references ... 7
3 Terms and definitions ... 10
4 Voltage designation and materials ... 11
5 Conductors ... 14
6 Insulation ... 14
7 Shield ... 15
8 Core, lining and filling of three-core cable ... 16
9 Metal layer of single-core or three-core cable ... 17
10 Metal shield ... 17
11 Concentric conductor ... 18
12 Lead sheath of the metal sheath ... 19
13 Metal armor ... 19
14 Outer sheath ... 22
15 Test conditions ... 24
16 Routine test ... 24
17 Sample test ... 26
18 Electrical type test ... 33
19 Non-electrical type test ... 37
20 Electrical tests after installation ... 50
21 Supplementary terms for cable products ... 51
Appendix A (Normative) Assumed calculation method for determining sheath
dimensions ... 52
Appendix B (Normative) Numerical rounding ... 58
Appendix C (Normative) HEPR insulation hardness measurement ... 60
Appendix D (Normative) Measurement method of semi-conducting shield resistivity
... 63
Appendix E (Normative) Water permeability test ... 66
Appendix F (Normative) Tests on cable assemblies with longitudinal metal foil
composite sheaths ... 68
Appendix G (Normative) Supplementary terms for cable products ... 71
Power cables with extruded insulation and their accessories
for rated voltages from 1 kV (Um = 1.2 kV) up to 35 kV (Um
= 40.5 kV) - Part 3: Cables for rated voltages of 35 kV (Um =
40.5 kV)
1 Scope
This Part of GB/T 12706 specifies the structure, dimensions and test requirements for
power cables with extruded insulation for a rated voltage of 35 kV fixedly mounted in
distribution networks or industrial installations.
This Part applies to cables of longitudinal water-blocking structure and their testing.
This Part does not apply to cables with special installation and operation conditions,
such as overhead cables, as well as cables used in the mining industry, in nuclear power
plants (in and near containments), and underwater or on ships.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 156, Standard voltages
GB/T 2951.11-2008, Common test methods for insulating and sheathing materials
of electric and optical cables - Part 11: Methods for general application -
Measurement of thickness and overall dimensions
GB/T 2951.12-2008, Common test methods for insulating and sheathing materials
of electric and optical cables - Part 12: Methods for general application - Thermal
ageing methods
GB/T 2951.13-2008, Common test methods for insulating and sheathing materials
of electric and optical cables - Part 13: Methods for general application -
Measurement for determining the density - Water absorption tests - Shrinkage test
GB/T 2951.14-2008, Common test methods for insulating and sheathing materials
of electric and optical cables - Part 14: Methods for general application - Test at low
temperature
IEC 60229:2007, Electric cables - Tests on extruded oversheaths with a special
protective function
IEC 61034-2, Measurement of smoke density of cables burning under defined
conditions - Part 2: Test procedure and requirements
ISO 48, Rubber, vulcanized or thermoplastic - Determination of hardness (hardness
between 10 IRHD and 100 IRHD)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 Terms related to size values
3.1.1
nominal value
A specified quantity value, which is often used in the table.
Note: In this Part, quantity values derived from nominal values are usually verified by
measurement taking into account specified tolerances.
3.1.2
approximate value
A value that is neither guaranteed nor checked.
Note: The approximate value may be used for calculations of other dimensional values.
3.1.3
median value
When several values obtained from the test are arranged in increasing (or decreasing)
order, if the number of values is an odd number, it is the middle value; if the number of
values is an even number, it is the average of the two middle values.
3.2 Terms related to testing
3.2.1
routine tests
Tests carried out by the manufacturer on all manufactured lengths of finished cables to
verify whether all cables comply with specified requirements.
3.2.2
sample tests
Tests carried out by the manufacturer at specified frequencies on finished cable samples
or on certain components taken from the finished cable to check whether the cable
complies with specified requirements.
3.2.3
type tests
Tests carried out on normal commercial principles before supply of a type of cable
covered by this Part to demonstrate that the cable has satisfactory performance under
the intended conditions of use.
Note: The characteristic of this test is that unless changes in the cable material or design
or manufacturing process may change the characteristics of the cable, there is
no need to redo the test after it has been done.
3.2.4
electrical tests after installation
Tests conducted after installation to prove that the installed cables and accessories are
intact.
4 Voltage designation and materials
4.1 Rated voltage
The rated voltage U0/U(Um) of the cables in this Part is marked as 21/35 (40.5) kV and
26/35 (40.5) kV.
In the voltage designation U0/U(Um) of the cable:
-- U0 is the rated power frequency voltage between the conductor for which the cable
is designed and earth or the metal shield;
-- U is the rated power frequency voltage between the conductors for which the cable
is designed;
-- Um is the maximum value of the “maximum system voltage” that the equipment
can use (see GB/T 156).
The rated voltage of a cable for a given application shall be appropriate for the operating
conditions of the system in which the cable is used. To facilitate cable selection, systems
are divided into the following three categories:
If the phase-separated metal shielded cable core of a cable has another overall metal
layer of the same metal material (see Chapter 9), the cable core shall be covered with a
lining on the outside. The lining and filling shall comply with 8.2. Semi-conducting
materials can also be used for the lining and filling.
When the metal materials used for the phase-separated and overall metal layers are
different, extruded isolation sleeves of any material complying with the provisions in
14.2 shall be used to separate them. For lead-sheathed cables, the isolation between the
lead sheath and the phase-separated cladding metal layer may use a lining that complies
with 8.2.
If the cable does not have an overall metal layer (see Chapter 9), the lining may be
omitted as long as the cable shape remains round.
9 Metal layer of single-core or three-core cable
This Part includes the following types of metal layers:
a) Metal shield (see Chapter 10);
b) Concentric conductor (see Chapter 11);
c) Lead sheath of the metal sheath (see Chapter 12);
d) Metal armor (see Chapter 13).
The metal layer shall consist of one or more of the above types and shall be non-
magnetic when covering a single-core cable or a separate insulated core of a three-core
cable.
Measures can be taken to provide longitudinal water-blocking properties around the
metal layer.
10 Metal shield
10.1 Structure
Metal shield shall consist of one or more concentric layers of metal strips, metal braids,
metal wires, or a combination of metal wires and metal strips.
The metal shield may be a metallic sheath or, in the case of overall shield, armor
complying with 10.2.
When selecting materials of metal shields, special consideration shall be given to the
possibility of corrosion, which is not only for mechanical safety but also for electrical
safety.
The overlap and gap of metal shields shall comply with the requirements of 10.2.
10.2 Requirements
10.2.1 The resistance of copper wire shield in metal shield shall comply with the
requirements of GB/T 3956 when applicable. The nominal cross-section of the copper
wire shield shall be determined based on the fault current capacity.
10.2.2 The copper strip shield shall consist of an overlapping layer of soft copper strip.
The nominal overlap rate between overlapping copper strips is 15% of the copper strip
width, and the minimum overlap rate shall not be less than 5%. Other structures can be
used when required.
The soft copper strip as the shielding raw material shall be selected to comply with the
regulations of GB/T 11091.
The nominal thickness of the copper strip is:
-- single-core cable: ≥0.12 mm;
-- three-core cable: ≥0.10 mm.
The minimum thickness of copper strip shall not be less than 90% of the nominal value.
10.2.3 The metal shield of cables with a nominal cross-sectional area of 500 mm2 and
above shall adopt a copper wire shielding structure. The copper wire shield shall be
composed of sparsely wound soft copper wire, and the surface can be tightened with
reversely wrapped copper wire or copper strip. The average gap between adjacent
copper wires shall not be greater than 4 mm. See 6.5.2 in GB/T 11017.2-2014 for the
definition and calculation of the average gap between adjacent copper wires. The total
resistance of copper wire shield in metal shield shall comply with the requirements of
GB/T 3956 when applicable.
11 Concentric conductor
11.1 Structure
The gap between concentric conductors shall comply with the requirements of 10.2.3.
When selecting concentric conductor structures and materials, special consideration
shall be given to the possibility of corrosion, which is not only for mechanical safety
but also for electrical safety.
11.2 Requirements
The size, physical properties and resistance requirements of concentric conductors shall
comply with the provisions of 10.2.
The metal strip shall be galvanized steel strip, stainless steel strip (non-magnetic),
aluminum strip or aluminum alloy strip. The steel strip shall be industrial grade hot-
rolled or cold-rolled steel strip.
When the armored steel wire layer is required to meet the minimum electrical
conductivity, the armored layer is allowed to contain sufficient copper wire or tinned
copper wire to ensure that the requirements are met.
When selecting armoring materials, especially when the armor is used as a shield,
special consideration shall be given to the possibility of corrosion, which is not only for
mechanical safety but also for electrical safety.
Unless special construction is adopted, the armor of single-core cables used in AC
systems shall be of non-magnetic material.
Note: Even if the single-core cable used in the AC system is armored mainly with
magnetic materials and adopts a special structure, the cable carrying capacity
will still be greatly reduced.
13.3 Application of armor
13.3.1 Single-core cable
There shall be an extruded lining layer under the armored layer of single-core cables,
and the thickness shall comply with 8.2.
13.3.2 Three-core cable
When three-core cables need to be armored, the armor shall be coated on a lining that
complies with 8.2.
13.3.3 Isolation sleeve
When the metal layer under the armor is different from the armor material, one of the
materials specified in 14.2 shall be extruded and wrapped with an isolation sleeve to
separate them.
The isolation sleeve shall withstand the spark test specified in GB/T 3048.10.
The isolation sleeve of halogen-free cable (ST8) shall comply with the requirements in
Table 5.
If the lead-sheathed cable requires an armor layer, isolation sleeves or tape-coated
cushions can be used, which shall comply with the provisions of 13.3.4.
If an isolation sleeve is used under the armor layer, it can be used instead of the lining
layer or in addition to the lining layer.
Cables with a longitudinal water-blocking structure around the metal layer do not need
an isolation sleeve.
The nominal thickness of the isolation sleeve shall be calculated according to Formula
(2):
Where:
tss – nominal thickness of the isolation sleeve, in millimeters (mm);
Du – assumed diameter before the isolation sleeve, in millimeters (mm).
The assumed diameter calculation shall be carried out according to Appendix A, and
the calculation result shall be rounded to 0.1 mm (see Appendix B).
When the calculated value of the nominal thickness of the non-lead sheathed cable
isolation sleeve is less than 1.2 mm, the nominal thickness of the isolation sleeve shall
be 1.2 mm. If the isolation sleeve is directly extruded onto the lead sheath, when the
calculated value of the nominal thickness of the isolation sleeve is less than 1.0 mm,
the nominal thickness of the isolation sleeve shall be 1.0 mm.
13.3.4 Tape cushion under lead sheathed cable armor
The tape cushion outside the lead sheath coating shall be composed of impregnated
paper tape and composite paper tape, or two layers of impregnated paper tape and
composite paper tape plus one or more layers of composite impregnated fiber material.
The impregnating agent for the cushion material can be asphalt or other preservatives.
For metal wire armor, these impregnating agents shall not be applied directly under the
metal wire.
Synthetic material tapes may also be used instead of impregnated paper tapes.
The approximate total thickness of the tape cushion between the lead sheath and the
armor after armoring is 1.5 mm.
13.4 Dimensions of armored metal wire and armored metal strip
Armored metal wire and armored metal strip shall preferably be of the following
nominal dimensions:
-- Round metal wire (thin): diameter 2.0 mm, 2.5 mm, 3.15 mm;
-- Round metal wire (thick): diameter 4.0 mm;
-- Flat metal wire: thickness 0.8 mm;
15 Test conditions
15.1 Ambient temperature
Unless otherwise specified, the test shall be conducted at ambient temperature
(20±15) °C.
15.2 Frequency and waveform of power frequency test voltage
The frequency of the power frequency test voltage shall be 49 Hz ~ 61 Hz, the
waveform shall be basically a sine wave, and the quoted value shall be the effective
value.
15.3 Waveform of impulse test voltage
According to GB/T 3048.13, the shock wave shall have an effective wave front time of
1 μs ~ 5 μs and a nominal half-peak time of 40 μs ~ 60 μs. Other aspects shall comply
with GB/T 16927.1.
15.4 Determination of cable conductor temperature
The cable conductor temperature during the test can be determined according to the
method specified in GB/T 12706.2.
16 Routine test
16.1 General
Routine tests shall normally be carried out on each manufactured length of cable (see
3.2.1). According to the quality control agreement reached between the purchaser and
the manufacturer, the number of test cables can be reduced or other test methods can be
used.
The routine tests specified in this Part are:
a) Conductor resistance measurement (see 16.2);
b) Partial discharge test (see 16.3);
c) Voltage test (see 16.4);
d) DC voltage withstand test of the outer sheath, when there is a semi-conductive
structure on the outer sheath of the cable (see 16.5).
16.2 Conductor resistance measurement
Resistance measurements shall be made on all conductors for each cable length in the
routine test, including concentric conductors if there are any.
Finished cables or samples removed from finished cables shall be stored in a test room
maintained at an appropriate temperature for at least 12 hours before testing. If there is
doubt whether the conductor temperature is consistent with room temperature, the cable
shall be stored in the test room for 24 hours before measurement. Alternatively, the
conductor sample can be placed in a temperature-controlled liquid tank for at least 1
hour before the resistance is measured.
The measured value of resistance shall be corrected to the value of 1 km length at 20 °C
according to the formula and coefficient given in GB/T 3956.
The DC resistance of each conductor at 20 °C shall not exceed the corresponding
maximum value specified in GB/T 3956. When the nominal cross-sectional area is
applicable, the resistance of the concentric conductors shall also comply with GB/T
3956.
The conductor DC resistance requirements of aluminum alloy conductors are consistent
with those of aluminum conductors of the same nominal cross-sectional area.
16.3 Partial discharge test
The partial discharge test shall be carried out according to GB/T 3048.12, and the test
sensitivity shall be 10 pC or better.
All insulated cores of a three-core cable shall be tested, with voltage applied between
each conductor and the metallic shield.
The test voltage shall be gradually increased to 2U0 and maintained for 10 s, and then
slowly reduced to 1.73U0.
At 1.73U0, there shall be no detectable discharge produced by the cable under test that
exceeds the declared test sensitivity.
Note: Any discharge from the cable under test may be harmful.
16.4 Voltage test
16.4.1 Overview
The voltage test shall be conducted at ambient temperature using power frequency AC
voltage.
Unless otherwise required by the purchaser, the manufacturer may choose the following
procedures for routine voltage test:
a) 3.5U0, 5 min;
18 Electrical type test
18.1 General
After a type of cable with a specific voltage and conductor cross-sectional area has
passed the type test of this Part, the type approval for cables with other conductor cross-
sections and/or rated voltages remains valid, as long as the following three conditions
are met:
a) The insulating and semiconducting shielding materials and manufacturing
processes used are the same;
b) The conductor cross-sectional area is not larger than the tested cable. However, if
the conductor cross-sectional area of the tested cable is between 95 mm2 and 630
mm2 (inclusive), all cables of 630 mm2 and below are also valid;
c) The rated voltage is not higher than the tested cable.
Type approval is independent of conductor material.
18.2 Sample
A cable test portion with a length of 10 m ~ 15 m shall be taken from the finished cable
for testing according to 18.3.
With the exception of 18.4, all tests listed in 18.3 shall be performed sequentially on
the same test portion.
Each test or measurement on three-core cables shall be made on all insulated cores.
The resistivity measurement of the semi-conducting shield specified in 18.11 shall be
carried out on a separate test portion.
18.3 Test sequence
The normal sequence of tests shall be as follows:
a) bending test and the subsequent partial discharge test (see 18.5 and 18.6);
b) tanδ measurement (see 18.7);
c) heat cycle test and the subsequent partial discharge test (see 18.8);
d) impulse voltage test and the subsequent power frequency voltage test (see 18.9);
e) 4 h voltage test (see 18.10).
18.4 Special terms
......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.