VV (VLV) PVC insulated PVC sheathed power cable
VY (VLY) PVC insulated and sheathed power cable
YJV (YJLV) XLPE insulated PVC sheathed power cable
YJY (YJLY) XLPE insulated PE sheathed power cable
Foot label 22 represents a steel belt armored PVC sheath
Foot label 23 represents a steel belt armored edge polychloroprene sheath
Foot label 32 represents a thin steel wire armored PVC sheath
Foot mark 33 represents a thin steel wire-filled polychloroolefin sheath
Foot mark 42 represents a thick steel wire armored PVC sheath
Foot label 43 represents a thick steel wire-filled polychloroolefin sheath
VV (VLV) type cable conductors operate at a maximum temperature of 70 degrees Celsius, and when short-circuited (duration is less than 5 seconds), the maximum temperature does not exceed 160 degrees Celsius.
YJV (YJLV) type cable conductors operate at a maximum temperature of 90 degrees Celsius, and when short-circuited (duration is less than 5 seconds), the maximum temperature does not exceed 250 degrees Celsius.
Mineral insulated cable. Magnesium oxide insulation, copper or superalloy sheath, operating at a maximum rated temperature of 250 degrees Celsius.
Due to the wide variety of special purpose cables, only a brief introduction is given here.
Fluoroplastic cable for high temperature environment, polyvinylidene fluoride insulated, sheathed cable continuous working temperature 150 degrees Celsius, polytetrafluoroethylene propylene insulation, sheathed cable continuous working temperature 100 degrees Celsius, PTFE insulation.
The sheathed cable has a continuous operating temperature of 260 degrees Celsius. Dingqing composite insulated cable for oil-contaminated environment, operating at a maximum rated temperature of 105 degrees Celsius.
Silicone rubber cable for use in a constantly moving environment with a maximum rated temperature of 180 degrees Celsius.
In addition, there are special low temperature, waterproof, pest control, mining cables and so on.
U0 is the conductor-to-ground voltage, U is the voltage between the conductor and the conductor, and Um is the maximum value of the highest voltage of the system in which the device is used.
Among them, U0 is divided into two categories according to the duration of system ground fault: the first type of cable---the system for single-phase ground fault time is generally no more than 1 minute, and can also be used for up to 8 hours, each year.
A system that does not exceed 125 hours in total; a second type of cable—for systems with longer ground faults or where cable insulation performance is critical.
For example, for a 10kV system, if the neutral point is grounded via an arc suppression coil, a 8.7/10kV cable (or 8.7/12) should be used.
If the neutral point is grounded via a small resistor, a 6/10kV cable (or 6/12) can be used.
Theoretically, the allowable current carrying capacity of the N line should be greater than the sum of the maximum three-phase unbalanced current and the zero-order harmonic current.
In engineering, in a system dominated by single-phase equipment, the N-line section is equal to the phase line section (ie, 4 equal core).
In a three-phase balance system or a system based on three-phase equipment, the N-line section is greater than or equal to Half of the phase line section (ie 3+1 core), with two exceptions: when the phase line is 35mm2, the N line is 16mm2, and when the phase line is 150mm2, the N line is 70mm2.
In systems with a large number of zero-order harmonic components, the N-line cross-section is equal to twice the cross-section of the phase line or customized according to actual needs.
In addition to the temperature rise, economic current density, voltage loss, mechanical strength, and current carrying capacity required in the design manual, you should also pay attention to:
1. Single-phase short-circuit fault caused by laying distance, ground fault protection sensitivity problem (low-voltage system)
2. Minimize and merge the section grades in a project to facilitate processing orders.
Among the commonly used cables, although the PVC sheathed power cable is superior to the polyethylene sheathed power cable in terms of waterproof performance, in the fire condition, the harmful gas released by the polyvinyl chloride far exceeds the polyethylene.
Almost all cable manufacturers produce PVC sheathed power cables, of which only some manufacturers produce polyethylene sheathed power cables.
flame retardant products can provide more than 15 times of escape time than non-flame retardant products; materials burned by flame retardant materials are only l/2 of non-flame retardant materials.
Heat release rate of flame retardant materials is only non-resistance l/4 of the burning material.
The total amount of toxic gas in the combustion product, as expressed by the equivalent amount of carbon monoxide, the flame retardant product is only l/3 of the non-flame retardant product.
The smoke generating performance of the ordinary flame retardant product and the non-flame retardant product.
There is no big difference in the amount of smoke produced.
Flame-retardant cables are classified into three categories A, B, and C according to the GB12666.5-90 standard.
Class A flame-retardant cables should be selected in engineering design.
Reducing the number of cables in the same fire barrier (eg the same bridge, the same shaft) helps to improve the flame retardancy of the cable.
According to GBl2666.6, the fire test temperature is divided into two categories: Class A is 950-1000 °C, and the test time is 90 minutes.
Class B is 750-800 °C and the evaluation time is 90 minutes.
That is, the cable is directly burned at an external fire source of 750-800 ° C (or 950-1000 ° C), and can still be energized within 90 minutes, and it is judged to be a Class B or Class A fire-resistant cable.
The organic fire-resistant cable is wrapped around the copper conductor with a mica refractory tape (800 ° C high temperature resistance) as a refractory layer, and then extruded with a certain thickness of normal insulation layer according to different types, and finally the inter-core inter-core filling layer and the outermost sheath and The same as a normal cable.
Inorganic is also called mineral insulated or magnesium oxide insulated cable.
The outer sheath is copper tube or special alloy tube. Magnesia is filled between the outer sheath and the copper conductor as the insulating material.
Because the melting point of magnesium oxide is 2800. °C, the melting point of the copper tube (outer sheath) is 1083 °C, the special alloy tube can guarantee no deformation at 825 °C, so as long as the outer sheath is not damaged, the cable can work normally, and its fire resistance far exceeds that of organic fireproof cable.
Do not easily ask for the use of Class A fire-resistant cables in engineering design, because NH-YJV or NH-VV generally do not meet Class A requirements, while mineral insulated cables are excellent in fire resistance.
But the cost is much higher than ordinary fire-resistant cables.
The requirements for construction are more stringent.
In addition, because it is a single-core cable, the relative N and PE spacing are different, and the single-phase short-circuit and ground short-circuit impedance (reactance) have certain differences.
V. Related terms
Oxygen index: refers to the minimum oxygen content required for a solid material to maintain a stable combustion in a mixed gas stream of oxygen and nitrogen under specified conditions.
A high oxygen index indicates that the material is not easily combusted, and a low oxygen index indicates that the material is easily burned.
The correspondence between the oxygen index (LOI) of a material and its flame retardancy is as follows:
LOI < 23 flammable
L24 - 28 slightly flame retardant
LOI 29 - 35 flame retardant
LOI > 36 high flame retardant
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