Detail of GB/T 12706.3-2020

Introduction of GB/T 12706.3-2020

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. GB/T 12706 consists of 4 parts under the general title Power cables with extruded insulation and their accessories for rated voltages from 1kV (Um=1.2kV) up to 35kV (Um=40.5kV): ——Part 1: Cables for rated voltage of 1kV (Um=1.2kV) and 3kV (Um=3.6kV); ——Part 2: Cables for rated voltages from 6kV (Um=7.2kV) up to 30kV (Um=36kV); ——Part 3: Cables for rated voltages of 35kV (Um= 40.5kV); ——Part 4: Test requirements on accessories for cables with rated voltages from 6kV (Um=7.2kV) up to 35kV (Um=40.5kV). This is Part 3 of GB/T 12706. This part replaces GB/T 12706.3-2008 Power cables with extruded insulation and their accessories for rated voltages from 1kV (Um=1.2kV) up to 35kV (Um=40.5kV) - Part 3: Cables for rated voltage of 35kV (Um= 40.5kV); In addition to editorial changes, the following main technical changes have been made with respect to GB/T 12706.3-2008: ——ST8 halogen free sheathing compound is added (see Clause 1 and Table 4); ——ST1 and ST3 sheathing materials are deleted (see Tables 4, 16, 18, 19 and 20; Tables 4, 13, 15, 16 and 17 of Edition 2008); ——Class 1 of copper conductor is deleted (see Clause 5; Clause 5 of Edition 2008); ——The requirements for insulation, inner coverings and fillers, separation sheath and oversheath of halogen free low-smoke flame-retardant cables are added (see 6.1, 8.2.2, 13.3.3, 14.2 and Table 5); ——Strippable insulation screen is added (see 7.3); ——The technical requirements for inner coverings and fillers are modified (see 8.2; 8.1 of Edition 2008); ——The calculation formula for nominal thickness of lead sheath are modified (see Clause 12; 12.1 of Edition 2008); ——The requirements for armouring materials are modified (see 13.2; 13.2 of Edition 2008); ——The requirements for the diameter of thick round metal wires and those for the nominal thickness of separation sheath or inner covering under armour are added (see 13.4, Table 8 and 13.6); ——The requirements for thickness of oversheath are modified (see 14.3; 14.3 of Edition 2008); ——The method for determination of the cable conductor temperature during test is added (see 15.4); ——The withstand test of oversheath with semi-conductive layer is added (see 16.1 and 16.5); ——The requirements for the thickness of non-metal sheath are modified (see 17.5.3 and 19.3; 17.5.3 and 19.2 of Edition 2008); ——The requirements for the measurement of overlap rate and gap rate of lapped tapes are added (see 17.11); ——The requirements for the diameter of bending test cylinder are modified (see 18.5; 18.1.3 of Edition 2008); ——Tests on mechanical properties, pressure at high temperature, behaviour at low temperature, burning behavior and water absorption of ST8 halogen free sheathing compound are added (see 19.5, 19.6, 19.9, 19.15 and 19.24); ——The flame spread test of cables is modified (see 19.15; 19.14 of Edition 2008); ——The applicable objects of the measurement of carbon black content of black PE oversheaths are modified (see 19.16; 19.15 of Edition 2008); ——The test methods and requirements for mechanical properties and particular characteristics of ST8 halogen free sheathing compound are added (see Tables 18 and 21); ——The requirements for increase in diameter due to the concentric conductor or metal screen are added (see Table A.2; Table A.2 of Edition 2008); ——The rounding rules for specified values are added (see B.3); ——The code of polyolefin oversheath is added (see G.1.1); ——The representation method of flame retardant cable products is added (see G.1.3); ——The requirements for delivery length and marking of finished cable are added (see G.2.2 and G.2.3); ——The recommendation of ambient temperature during installation of halogen-free flame-retardant sheathed cables is added (see G.3.1). This part was proposed by the China Electrical Equipment Industrial Association. This part is under the jurisdiction of SAC/TC 213 National Technical Committee on Wires and Cables of Standardization Administration of China. The previous editions of this part are as follows: ——GB12706.3-1991, GB/T 12706.3-2002 and GB/T 12706.3-2008; ——GB12706.1-1991. Power cables with extruded insulation and their accessories for rated voltages from 1kV (Um=1.2kV) up to 35kV (Um=40.5kV) - Part 3: Cables for rated voltages of 35kV (Um=40.5kV) 1 Scope This part of GB/T 12706 specifies the construction, dimensions and test requirements of power cables with extruded insulation for rated voltage of 35kV for fixed installations such as distribution networks or industrial installations. This part is applicable to cables with longitudinal watertightness and their tests. Cables for special installation and service conditions are not included, for example cables for overhead networks, the mining industry, nuclear power plants (in and around the containment area) nor for submarine use or shipboard application. 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 - Tests for determining the mechanical properties 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 GB/T 2951.21-2008 Common test methods for insulating and sheathing materials of electric and optical cables - Part 21: Methods specific to elastomeric compounds - Ozone resistance, hot set and mineral oil immersion tests GB/T 2951.31-2008 Common test methods for insulating and sheathing materials of electric and optical cables - Part 31: Methods specific to PVC compounds - Pressure test at high temperature - Test for resistance to cracking GB/T 2951.32-2008 Common test methods for insulating and sheathing materials of electric cables - Part 32: Methods specific to PVC compounds - Loss of mass test - Thermal stability test GB/T 2951.41-2008 Common test methods for insulating and sheathing materials of electric and optical cables - Part 41: Methods specific to polyethylene and polypropylene compounds - Resistance to environmental stress cracking - Measurement of the melt flow index - Carbon black and/or mineral filler content measurement in polyethylene by direct combustion - Measurement of carbon black content by thermo gravimetric analysis (TGA) - Assessment of carbon black dispersion in polyethylene using a microscope GB/T 3048.10 Test methods for electrical properties of electric cables and wires - Part 10: Spark test of extruded protective sheaths GB/T 3048.12 Test methods for electrical properties of electric cables and wires - Part 12: Partial discharge test GB/T 3048.13 Test methods for electrical properties of electric cables and wires - Part 13: Impulse voltage test GB/T 3956 Conductors of insulated cables GB/T 6995.3 Markings for electric cables and wires - Part 3: Identifications of cables and wires GB/T 7113.2 Flexible insulating sleeving - Part 2: Methods of test GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values GB/T 11017.2-2014 Power cables with cross-linked polyethylene insulation and their accessories for rated voltage of 110kV (Um=126kV) - Part 2: Power cables GB/T 11091 Copper strip for cables GB/T 12706.1 Power cables with extruded insulation and their accessories for rated voltages from 1kV (Um=1.2kV) up to 35kV (Um=40.5kV) - Part 1: Cables for rated voltage of 1kV (Um=1.2kV) and 3kV (Um=3.6kV) GB/T 16927.1 High-voltage test techniques - Part 1: General definitions and test requirements GB/T 17650.1 Test on gases evolved during combustion of materials from cables - Part 1: Determination of the amount of halogen acid gas GB/T 17650.2 Test on gases evolved during combustion of materials from cables - Part 2: Determination of degree of acidity of gases by measuring pH and conductivity GB/T 18380.11 Tests on electric and optical fibre cables under fire conditions - Part 11: Test for vertical flame propagation for a single insulated wire or cable - Apparatus GB/T 18380.12 Tests on electric and optical fibre cables under fire conditions - Part 12: Test for vertical flame propagation for a single insulated wire or cable - Procedure for 1kW pre-mixed flame GB/T 18380.13 Tests on electric and optical fibre cables under fire conditions - Part 13: Test for vertical flame propagation for a single insulated wire or cable - Procedure for determination of flaming droplets/particles GB/T 18380.33 Tests on electric and optical fibre cables under fire conditions - Part 33: Test for vertical flame spread of vertically-mounted bunched wires or cables - Category A GB/T 18380.34 Tests on electric and optical fibre cables under fire conditions - Part 34: Test for vertical flame spread of vertically-mounted bunched wires or cables - Category B GB/T 18380.35 Tests on electric and optical fibre cables under fire conditions - Part 35: Test for vertical flame spread of vertically-mounted bunched wires or cables - Category C GB/T 18380.36 Tests on electric and optical fibre cables under fire conditions - Part 36: Test for vertical flame spread of vertically-mounted bunched wires or cables - Category D GB/T 19666 Flame retardant and fire resistant wires and cables JB/T 8137 (all parts) Delivery drums for wires and cables JB/T 8996 Guide to the selection of high-voltage cables JB/T 10696.6 Test methods for determining mechanical, physical and chemical properties of electric cables and wires - Part 6: Test for abrasion of oversheaths 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 concerning dimensional values 3.1.1 nominal value value by which a quantity is designated and which is often used in tables Note: Usually, in this part, nominal values give rise to values to be checked by measurements taking into account specified tolerances. 3.1.2 approximate value value which is neither guaranteed nor checked Note: It is used, for example, for the calculation of other dimensional values. 3.1.3 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 3.2 Definitions concerning the tests 3.2.1 routine tests tests made by the manufacturer on each manufactured length of cable to check that each length meets the specified requirements 3.2.2 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 3.2.3 type tests tests made before supplying, on a general commercial basis, a type of cable covered by this part, in order to demonstrate satisfactory performance characteristics to meet the intended application Note: These tests are of such a nature that, after they have been made, they need not be repeated, unless changes are made in the cable materials or design or manufacturing process which might change the performance characteristics. 3.2.4 electrical tests after installation tests made to demonstrate the integrity of the cable and its accessories as installed 4 Voltage designations and materials 4.1 Rated voltages The rated voltages U0/U(Um) of the cables considered in this part are 21/35(40.5)kV and 26/35(40.5)kV. In the voltage designation of cables U0/U (Um): ——U0 is the rated power frequency voltage between conductor and earth or metal 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 (see GB/T 156). The rated voltage of the cable for a given application shall be suitable for the operating conditions in the system in which the cable is used. To facilitate the selection of the cable, systems are divided into three categories: ——Category A: this category comprises those systems in which any phase conductor that comes in contact with earth or an earth conductor is disconnected from the system within 1min. ——Category B: this category comprises those systems which, under fault conditions, are operated for a short time with one phase earthed. This period, according to JB/T 8996, shall not exceed 1h. For cables covered by this part, a longer period, not exceeding 8h on any occasion, can be tolerated. The total duration of earth faults in any year shall not exceed 125h. ——Category C: this category comprises all systems which do not fall into Category A or B. Note: It should be realized that in a system where an earth fault is not automatically and promptly isolated, the extra stresses on the insulation of cables during the earth fault reduce the life of the cables to a certain degree. If the system is expected to be operated fairly often with a permanent earth fault, it may be advisable to classify the system in Category C.

Contents of GB/T 12706.3-2020

Foreword III 1 Scope 2 Normative references 3 Terms and definitions 4 Voltage designations and materials 5 Conductors 6 Insulation 7 Screening 8 Assembly of three-core cables, inner coverings and fillers 9 Metal layers for single-core and three-core cables 10 Metal screen 11 Concentric conductor 12 Lead sheath 13 Metal armour 14 Oversheath 15 Test conditions 16 Routine test 17 Sample tests 18 Electrical type tests 19 Non-electrical type tests 20 Electrical tests after installation 21 Supplementary terms for cable products Annex A (normative) Fictitious calculation method for determination of dimensions of protective coverings Annex B (Normative) Rounding of numbers Annex C (Normative) Determination of hardness of HEPR insulations Annex D (Normative) Method of measuring resistivity of semi-conducting screens Annex E (Normative) Water penetration test Annex F (Normative) Test on cable assembly with longitudinally wrapped metal foil composite protective covering Annex G (Normative) Supplementary terms of cable products Bibliography Figure C.1 Test on surfaces of large radius of curvature Figure C.2 Test on surfaces of small radius of curvature Figure D.1 Measurement of the volume resistivity of the conductor screen Figure D.2 Measurement of the volume resistivity of the insulation screen Figure E.1 Schematic diagram of apparatus for water penetration test Figure F.1 Test on metal foil bond strength Figure F.2 Example of metal foil overlap Figure F.3 Bond strength test at metal foil overlap Figure G.1 Composition and arrangement sequence of product model Table 1 Recommended rated voltages U Table 2 Insulating compounds Table 3 Maximum conductor temperatures for different types of insulating compound Table 4 Maximum conductor temperatures for different types of sheathing compound Table 5 Test methods and requirements for halogen free compounds Table 6 Nominal thickness of insulation Table 7 Thickness of extruded inner covering Table 8 Nominal diameter of round armour wires Table 9 Nominal diameter of armour tapes Table 10 Routine test voltage Table 11 Number of samples for sample tests Table 12 Voltages for sample tests Table 13 Test requirements for particular characteristics of various thermosetting insulating compounds Table 14 Test requirements for particular characteristics of elastomeric sheathing compound Table 15 Electrical type test requirements for insulating compounds Table 16 Non-electrical type tests Table 17 Test requirements for mechanical characteristics of cable insulation (before and after ageing) Table 18 Test requirements for mechanical characteristics of sheathing compounds (before and after ageing) Table 19 Test requirements for particular characteristics for PVC sheathing compounds Table 20 Test requirements for particular characteristics of PE (thermoplastic polyethylene) sheathing compounds Table 21 Test requirements for particular characteristics for halogen free sheathing compounds Table A.1 Fictitious diameter of conductor Table A.2 Increase in diameter for concentric conductors and metal screens Table B.1 Rounded digits of specified value, determined value or calculated value Table G.1 Common cable models Table G.2 Minimum bending radius during cable installation