Power cables are used to transmit electricity on civil, low, medium or high voltage networks. In addition to power cables, products manufactured based on the same manufacturing process as electrical cables are signal cables, control cables… however, within the scope of this article we will only refer to cables. electricity.
As defined above, power cables play a particularly important role in the national power grid system when it plays a decisive role in the continuous operation of the entire system.
Specifically, electric cables are used to transmit electricity from a place of power supply such as a power plant to a place of electricity consumption such as houses, hospitals, schools, constructions, factories, etc. regional or provincial power networks, from the provincial network to the district and commune power grids…
Recognizing the particularly important role of power cables for the national power grid system, which directly affects other industries, especially the economy, the production of power cables is strictly regulated. in Vietnamese standards such as TCVN 6447, TCVN 5935, TCVN 6610, TCVN 5064, TCVN 5934, TCVN 5933…
So to have a basic understanding of electrical cables, continue to learn the information below.
1. Classification of electrical cables
Power cables have many types produced for many different purposes, to be able to easily distinguish the types of power cables need to be based on its name. Here, the power cable consists of the wire and the power cable .
- Electric wire used to transmit current for the civil power network up to 450/750V;
- Power cables are used to transmit current for low voltage networks up to 0.6/1kV, medium voltage up to 36kV and high voltage up to 500kV. Power cables include twisted-pair cables, low-voltage cables, medium-voltage cables, bare electrical cables, and fire-resistant cables.
Civil wires are specified according to TCVN 6610-3 and TCVN 6610-5, electric cables are regulated according to TCVN 5935-1, TCVN 5935-2, TCVN 6447, TCVN 5064… and many related documents. .
2. Construction of electric cables
Although specified in many different standards, basically, all types of electrical wires/cables have the same structure including conductive core, insulating material and sheath. All these structural layers. are specified in the TCVN and all fall within the following criteria:
- Pure copper conductor, pure aluminum conductor, aluminum conductor combined with galvanized steel. The conductor core consists of many copper/aluminum/aluminum steel cores, which are electrical engineering circular fibers (according to TCVN 5934:1995);
- Insulating material: is the next layer after the conductive core. The insulating material can be thermoplastic PVC, thermosetting XLPE (cross-linked polyethylene)/EPR (ethylene propylene rubber)/HEPR (high hardness ethylene propylene rubber).
- The sheath can be thermoplastic PVC or elastomeric material.
The conductive core of an electric cable consists of many copper or aluminum wires concentrically twisted and twisted to form several layers, the latter layer must be twisted in the opposite direction of the previous layer. The layers may or may not be pressed together.
For some special electrical cables such as underground cables, there is also a shielding or semiconductor layer between the upper layers, which we will learn later.
3. Power cable standards
Documents specifying core structure standards, requirements on insulation and sheathing, requirements on production standards of electric cables include: TCVN 5935-1, TCVN 5935-2, TCVN 6447, TCVN 6610, TCVN 5064. The basic content of each document is as follows:
TCVN 6610: Insulated flexible wire (civil electrical wire)
TCVN 6610 is divided into TCVN 6610-3:2000 and TCVN 6610-5: 2014 .
TCVN 6610-3
TCVN 6610-3:2000 regulates unsheathed single-core electrical wires (only PVC insulation) as follows:
- Single-core unsheathed cable with solid conductor and conductor temperature of 70 degrees Celsius for internal installation (6610 TCVN 05 or 227 IEC 05): Rated voltage up to 300/500V, number of conductors 1 and grade 1 conductors (solid 1-stranded rigid conductor), PVC/C insulation thickness from 0.6mm, average outer diameter from 1.9mm, maximum conductor temperature in normal use is 70 degrees Celsius;
- C pressure is not jacketed cores with conductor soft and temperature conductor is 70 degrees C for installation inside (6610 ISO 06 or 227 IEC 06): nominal voltage 300 / 500V, the number of conductor 1 and class 5 conductors (soft conductors), PVC/C insulation thickness from 0.6mm, average outer diameter from 2.1mm, maximum conductor temperature in normal use is 70 degrees Celsius.
TCVN 6610-5
TCVN 6610-5:2014 specifies electrical wires with more than 2 cores (from 2 to 5 conductor cores) and sheathed as follows:
- Flat tinsel wire (6610 TCVN 41/60227 IEC 41): Nominal voltage 300/300V, 2 conductors, PVC or PVC/D insulation thickness 0.8mm;
- Flexible cord for indoor decorative lighting (6610 TCVN 43/60227 IEC 43): Rated voltage 300/300V, number of class 1 and class 6 conductors (softer than class 5 conductors), insulation thickness power PVC or PVC/D medium 0.7mm;
- Light PVC sheathed wire (6610 TCVN 52/60227 IEC 52): Rated voltage 300/300V, 2 and 3 class 5 conductors (soft conductors), average 0.5mm PVC or PVC/D insulation; average sheath thickness 0.6mm;
- Common PVC sheathed flexible wire (6610 TCVN 53 or 60227 IEC 53): Rated voltage 300/500V, number of conductors from 2 to 5 and class 5 conductors, average PVC or PVC/D insulation from 0.6mm; average thickness of PVC or PVC/ST5 sheath from 0.8mm;
- Flexible wire with lightweight PVC sheathed heat-resistant for conductors with a maximum temperature of 90 degrees Celsius (6610 TCVN 56 or 60227 IEC 56): Rated voltage 300/300V, number of conductors from 2 to 3 and conductors grade 5 conductor, average 0.5mm PVC or PVC/E insulation; average thickness of PVC or PVC/ST10 sheath 0.6mm;
- Heat-resistant ordinary PVC sheathed flexible wire for conductors with a maximum temperature of 90 degrees Celsius (6610 TCVN 57 or 60227 IEC 57): Rated voltage 300/500V, number of conductors from 2 to 5 and conductors grade 5 conductor, average 0.6mm PVC or PVC/E insulation; average PVC or PVC/ST10 sheath thickness from 0.8mm.
TCVN 6447:1998: Twisted power cable
This standard specifies the construction, dimensions and tests for twisted-pair electrical cables (hereinafter referred to as cables) for outdoor use, insulated with cross-linked polyethylene (XLPE) operating voltages up to 0.6 /1 kV, with 2, 3 or 4 cores, with aluminum conductors, rated cross-section from 16 to 150 mm2.
1. For conductive core
The conductor shall be of aluminum braided from technical round and pressed aluminum strands. Dimensions and specifications of conductors must be in accordance with table 1. Aluminum wires used to braid the conductor walls must comply with TCVN 5934 – 1995.
The successive layers of helix must be in opposite directions and the outermost helix must be in the right direction.
2. For insulating sheath
Insulation shall be made of XLPE material having an ash content of not less than 2% by mass. Insulation shall be uniform, firmly adhered to the conductor but still able to be separated from the conductor, and comply with tables 1 and 2 of this standard.
Insulating material can be XLPE with symbol X-90 or special XLPE with higher heat resistance, symbol X-FP-90.
3. How to identify cable core
Cable cores shall be identified by continuous floating ribs along the length of the core.
Phase cores shall have the following embossed ribs:
- for two-core cables: one ribbed float;
- for three-core cables: one core has floating ribs, the other core has two floating ribs;
- for four-core cables: one core has embossed ribs, another core has two floating ribs and the third core has three floating ribs.
TCVN 5064:1994: Bare electrical cables
Bare electrical cables are specified according to TCVN 5064:1994 about bare wires used for overhead power transmission lines, including: bare copper cables, bare aluminum cables, bare aluminum cables with steel cores. The basic content provides for:
- Parameters of nominal cross-sectional area, number and diameter of constituting fibers, number of twisted layers, breaking force, maximum conductor resistance at 20 degrees C.
- Structural requirements:
- Conductors must have a uniform surface, braids without overlapping, twisted or broken as well as other defects harmful to the process of use.
- The successive layers must be in the opposite direction and the outermost spiral in the right direction. Twisted layers must be tight.
- The steel wires of the steel core aluminum wire must be galvanized to prevent rust, the zinc coating will not peel or crack when tested on the core, and may or may not be greased with anti-rust grease.
- There shall be no more than 5 splices on any one strand of the outermost layer of yarn over the fabricated length. The distance between the joints is not less than 15m, the joints must be welded by fire welding method.
- No joints on single-strand steel cores are allowed.
TCVN 5935: Low voltage cables and medium voltage cables
Low voltage cable is used to transmit voltage up to 0.6/1kV, medium voltage cable is used to transmit voltage up to 36kV. TCVN 5935 is divided into 5 parts, including TCVN 5935-1: 2013 regulations on electric cables used to transmit voltage up to 0.6/1kV (low voltage cables), TCVN 5935-2:2013 regulations on power cables used for transmission voltage up to 36kV (Medium voltage cable) and sections specifying test requirements.
TCVN 5935-1:2013
- Nominal voltage 0.6/1 (1.2) kV;
- Insulating compound
- PVC thermoplastic;
- Cross-linked insulating compound: Ethylene propylene rubber or the like (EPR), molecular rubber or high hardness ethylene propylene rubber (HEPR), Cross-linked polyethylene (XLPE).
- The maximum conductor temperature in normal operation is 70 degrees C (if PVC insulation) and 90 degrees C (if XLPE insulation).
- Conductors: Must be class 1 (1 solid conductor) or class 2 (braided conductor) (according to IEC 60228:2004) of annealed copper/coated with aluminum or aluminum alloy;
- Regulations on the minimum thickness of each insulating compound on each product classified according to the following nominal cross-sections: 1.5 and 2.5mm2, 4 and 6mm2, 10 and 16mm2, 25 and 35mm2, 50mm2, 70mm2, 95mm2, 120mm2, 150mm2, 185mm2, 240mm2, 300mm2…
TCVN 5935-2:2013
- The rated voltage Uo/U(Um) of the cables considered in this standard is as follows: Uo/U(Um) = 3.6/6 (7.2) – 6/10 (12) – 8.7 /15 (17.5) – 12/20 (24) – 18/10 (36) kV.
- Insulating compound
- PVC/B for cable lines with rated voltage Uo/U = 3.6/6 kV;
- Thermosetting plastic: Ethylene propylene rubber or similar (EPR), High hardness ethylene propylene rubber or rubber (HEPR), Cross-linked polyethylene (XLPE);
- Maximum conductor temperature in normal operation: For PVC/B it is 70 degrees Celsius, for EPR/ HEPR/ XLPE it is 90 degrees Celsius.
- Conductors: shall be class 1 (1 solid conductor) or class 2 (braided conductor) of metallized annealed copper with aluminum/aluminum alloy in accordance with IEC 60228.
- Specifies the nominal thickness of insulation layers PVC/B, XLPE, EPR/HEPR;
- Specifications for three-core cable assemblies, inner sheaths and fillers.
