The characteristic of flame-retardant wires and cables is to delay the spread of flames along the cables and prevent the spread of fire. Due to its low cost, it is widely used in fireproof cables. Whether a single cable or a bundle of cables is laid, when the cable burns, the spread of the flame can be controlled within a certain range to avoid major disasters caused by flame retardant fires and delays, thereby improving the fire protection level of cable lines.

When using cables, cable breakdown, cable conductor damage, core breakage and other faults may occur. Flame-retardant cables have a smaller conductor cross-sectional area and may break when the cable is squeezed. So how to check for broken wires in flame-retardant cables?

1. How to energize the capacitor

In this regard, some cable manufacturers usually use the capacitance comparison method to find out the approximate location of the broken wire. Using continuous power to precisely determine the break point of a cable is inefficient. It usually takes about an hour and a half to find the disconnection point. Using this method, it is almost impossible to find the broken core of the flame-retardant wire and cable that has completed the shielding, armoring and sheathing process. If it is not manufactured properly, the flame-retardant cable will be scrapped. This method is basically no longer used.

2. Combination of capacitance method and induction method:

This method is used to break the cable core, which requires no metal coating or extruded protective layer outside the cable core. The induced voltage method is to connect one end of the broken core of the cable to 650 V AC voltage, the other end to ground with other cores, and then use an induction pen that can emit a light signal to test.

3. Method of combining constant current source and bridge

This method is used on finished cables or cable cores covered with a metal layer. The method of searching is to first use a constant current source to burn out the insulation at the broken core of the flame-retardant cable, and then use the bridge method fault locator to accurately locate the fault point. This is also a commonly used method.

The analysis of the causes of wire and cable explosions and fires is as follows:

1. Short circuit defects caused by insulation damage: The maintenance lead sheath of wires and cables is damaged during the laying process or the cable insulation is mechanically damaged during operation, causing insulation breakdown between cables or between lead sheaths, and arcs causing insulation data and The data on the protective layer outside the cable is burning.

2. Long-term overload operation of wires and cables: Long-term overload operation, when the operating temperature of the cable insulation data exceeds the maximum allowable temperature for normal heating, the cable insulation will age monotonically, which generally occurs in the entire cable line. Due to the monotonous aging of cable insulation, the insulation data loses or reduces the insulation function and mechanical function, so it is easy to cause breakdown and burning, and even burn in multiple places along the entire length of the cable and burn together.

3. Oil-immersed cables drip and leak due to height differences: When the height difference of oil-immersed cables is large, oil dripping may occur. The flow effect makes the upper part of the cable monotonous due to the loss of oil. The thermal resistance of this part of the cable increases, causing premature coking and breakdown of the paper insulation. In addition, as the oil from the upper part drips down, a space is formed at the upper cable head and negative pressure is generated, making the cable easy to absorb moisture and make the end end damp. The static pressure due to oil accumulation in the lower part of the cable is large, causing oil leakage at the cable head. Cable moisture and oil leakage increase the likelihood of failure and fire.

4. Insulation breakdown of the core wire joint box: The core wire joints of the wire and cable joint box are oxidized, heated and degummed during operation due to loose crimping, weak welding or improper selection of joint data; when making the cable intermediate joint, pour it into the middle The quality of the insulating agent in the joint box does not meet the requirements. When pouring insulating agent, there are pores in the box. Due to poor sealing, the cable box is damaged and moisture leaks out of the cable box. All these factors can cause insulation breakdown, form a short circuit, and cause cable explosions and fires.

5. Burning of the cable head: Due to the moisture and dirt on the surface of the cable head, the porcelain sleeve of the cable head is cracked, and the lead spacing is too small, resulting in flashover and fire, and the surface insulation of the cable head and the lead insulation are burned.

6. Cable fires caused by external fire sources and heat sources: such as oil system fire extension, oil circuit breaker explosion fire extension, boiler pulverizing system or coal transportation system spontaneous combustion of pulverized coal, high-temperature steam pipe baking, acid-base chemical corrosion, welding sparks All types of fire can cause cable fires.