Causes and repair methods of water-cooled cable open circuit failure

I cavo raffreddato ad acqua consists of the cooling water pipe in the center, the surrounding wires, the rubber tube outside the wire, and the outside of the rubber tube. From the inside to the outside, there are a whole cylindrical shape with layers of shielding layer, heat insulation layer, and metal jacket layer. The utility model not only has many advantages of ordinary water-cooled cables, but also changes the disadvantages of the existing technology of exposing the outer rubber tube. The metal corrugated tube jacket is not afraid of sparks splashing, will not age, and it will not be charged during work, and has a good heat insulation effect. , Long life, is a novel power supply cable used in electric furnaces and electric arc furnaces in the metallurgical industry, and it is also an ideal water-cooled power supply cable for ferroalloy electric furnaces.

Due to the special structure of the water-cooled cable, it is different from the general cable fault judgment. Here is an example.

1. Fenomeno

After entering the secondary material in the electric arc furnace, it is switched on and smelted. No. 2 electrode (V phase) has no arcing. No. 1 (W phase) and No. 3 (U phase) electrodes can start arcing, but the arc is weak. The cross-section of the V-phase water-cooled cable is 3500 square millimeters, and two cables are arranged in parallel. It is generally considered that the possibility of two cables being short-circuited at the same time is very small.

2. Judgment

Adjust the secondary voltage of the arc furnace transformer to 360V, close the switch, first measure the V-phase secondary voltage with a multimeter, which is the normal value; but this value is the measured value when there is no large current, and it does not mean that the cable is intact (because The resistance value of a large cross-section water-cooled cable does not necessarily become infinite after the circuit breaks. For example, there is a resistance value of several thousand ohms. For instruments with high internal resistance such as multimeters, the voltage drop will be very small, so the multimeter will display The voltage is basically normal). For this reason, it is necessary to install a test load and perform the test (because after adding a larger power load to the disconnected water-cooled cable, the voltage of several thousand ohms on the line almost drops the voltage, and the multimeter can display Abnormal voltage). For example, connect two 500W light bulbs in series and install them on the conductive cross arm, close the switch and energize. If the light bulb does not light up, the V-phase voltage is measured at this time, and there is no reading, indicating that both cables have been disconnected.

3. Questioni che richiedono attenzione

(1) The power of the test load should be large enough to allow a certain current to pass through the water-cooled cable to facilitate judgment;

(2) Before the load test, adjust the secondary voltage of the arc furnace transformer to below 400V for safety.