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The common problems of single core steel tape armoured cable

Information Source:Henan Huadong Cable Co., Ltd Release date:2014-06-12

A single core cable steel tape armored caused the problem, Huadong repeatedly mentioned the single core steel tape armoured cable can not be used for the AC line and start and stop frequently in the DC line, why? According to the electromagnetic conversion principle, when the conductor steel tape armoured single core cable through alternating current (frequent starting and stopping the equivalent of alternating current), armored steel has a high magnetic conductivity, formation of eddy current in the strip (similar in principle of intermediate frequency furnace), the steel with high fever, the temperature in a very short period of time, resulting in the cable insulation layer melt or accelerated aging, insulation damage, resulting in the breakdown electric cable. If a terminal is not strip with good ground, because the strip between each ring does not guarantee good contact resistance characteristics and the strip itself, conductor and steel may form a "current transformer", potential in some range will produce higher, dangerous. According to the law of conservation of energy, steel heat to electricity consumption, will make the drop cable on the increase, and then use electrical equipment does not start properly, or even damage. Because there have some area must use the armoured cable, can have effectively solve problems such as environment, insect pest. What shall I do? The steel wire armored cable, aluminum tape armored cable, stainless steel armored cable or directly using the armoured multicore cable (single).

One case: We assist customers produced by other manufacturers of at least four single steel core armored cable accident -- cable is, the shorter length, the failure time is about 3 to 5 years; failure is the breakdown.

Case two: We assist customers produced by other manufacturers at least once a single core steel armored cable accident -- cable, about 500 meters in length, fault phenomenon first with N line breakdown, after the replacement, the motor can not start, line drop; recommends that customers use 3+2 cable, problem solving.

Analysis: the case of visible, steel wire armored cable on the line, at least will shorten the service life of the cable. The reason for adopting steel tape armoured single core cable is: because the buyer to understand the design drawings on the cable model errors, and subjective change specifications. When the steel tape armoured single core cable in length is short, the actual current flow through a much smaller than the maximum cable itself, the service life of the cable in the discount; when the maximum load flow length is longer or the current near the cable fault immediately appear. Treatment method of procurement, design specifications can be written in the same. In the AC line and frequent starting and DC line stop, do not use steel tape armoured single core cable, not the non-magnetic armoured single core cable in magnetic ducts alone laying. A single conductor around if there is a closed iron magnetic material, alternating magnetic field through the alternating current will produce eddy current problems in ferromagnetic materials. Multi core cable because of the inflow and outflow of current equal to (normal operation), no electromagnetic induction problem. Eddy current problem can lead to decreased sensitivity, cable protection device heating, line loss increased, shortened life expectancy, there may cause fire severity. If a single core armoured cable is required for communication system, can be made of stainless steel, copper, aluminum alloy and other non ferromagnetic material armoring or take a strip to prevent eddy current measures. Similarly, should avoid single core cable in steel pipe and the use of separate closed ferromagnetic materials such as cable clamp. Single core armored power cable has great limitation in use, is not reasonable in structure, concrete analysis is as follows.

By "field" that, when steel tape armoured single core cables during normal operation, the conductor will greatly by alternating current (DC cable frequent start stop is also equivalent to the alternating current), so around the cable will produce alternating electromagnetic field greatly, and armored steel with good permeability properties, in operation in the main, secondary coil strip and the conductor is similar to the current transformer, the electromagnetic field with alternating across the strip, will be induced by alternating current, and the strip itself with resistance is bigger, cause self heating, thus forming the eddy current loss and hysteresis loss in the steel belt, so in a short period of time, the strip can produce high temperature, coupled with the conductor in the normal operation of heat, if the heat can not be distributed in a timely manner (such as laying underground etc.), will cause the cable insulation layer melt or accelerated aging, insulation failure of the cable, causing the breakdown of the cable or early retirement.

At present, many domestic enterprises to adopt steel wire armored with copper wire isolation structure of single core armored cable, in fact, this "magnetic" structure is not reasonable, magnetic separation structure is designed to increase the magnetic circuit reluctance, reduce the magnetic induction intensity in wire, thereby reducing wire loss, but in the actual operation, the lines of force distortion caused by copper wire only, without interruption the magnetic lines of force, that is to say not to increase the reluctance of objective, the concrete analysis in Shanghai Electric Cable Research Institute senior expert Professor Ma Guodong in the "discussion" single core wire armoured power cables structure and works "wire and cable ampacity". In "cable ampacity" Professor Ma Guodong a book through a lot of experiments prove that the single core cable with steel wire armored with copper wire isolation structure can reduce the cable ampacity (Note: water low laying cable, not on the table), but the steel wire armored cable can withstand large tensile stress, is still widely used at present.

Therefore, for the single core cable, we can't use the magnetic material armoring, and should consider the non magnetic materials used instead, such as copper alloy wire (belt), stainless steel wire (belt), aluminum alloy wire (belt) etc.. In this regard, sales and customer contact process, if meet customer requirements for single core cable with steel tape armored structure, should try to clarify the reason why customers a single core cable can not be used in steel armor, and the use of non magnetic materials armoured cable is recommended.

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