Daily Maintenance Work for Cables

HIMALAYAL - SHANGHAI - CHINA

1. Load Monitoring    

Monitoring the cable load can help us learn the change of cable line load and analyze how the cable line works. The load of cables should be measured and monitored on a regular basis now that overload does considerable harm to the cable. The clip-on ammeter can be used to measure the load of cable lines. In order to avoid the premature aging of cable insulation, line voltage should not be very high - lower than 15% of rated voltage.  

2. Temperature Monitoring

The operation of cable line will be affected by the environment and heat dissipation. Besides, the temperature tends to at the earlier stage of the fault. Therefore, it is necessary to monitor the temperature of cable lines.     

Various instruments are used to measure the temperature of cable line sheaths, cable joints and other parts to prevent cable insulation from exceeding a limit and extend cable lifespan. 

The best time to measure the temperature of cables is in summer or when cable load is maximum. The soil temperature should be measured when measuring the temperature of direct burial cable. The distance from a place where thermoelectric thermometer is installed to cable should not be less than 3m.

The infrared thermometer is recommended to inspect and keep track of the cooling head of the cable, which is newly put into operation; staff should be arranged to tighten the joints during the maintenance period.   

3. Corrosion Monitoring   

The cable corrosion generally refers to the corrosion of metal plumbum or aluminum sheath and can be divided into two categories: chemical corrosion and electrolysis corrosion. 

Methods to prevent chemical corrosion are as follows: ① collect the soil and make chemical analysis to determine the degree of soil and underground water corrosion; ② take measures to change the route and upgrade poor soil or put the cables in the corrosion-resistant tubes; ③ If the cables are found to be corroded or chemicals leak from cable lines, it is suggested to dig the ground and inspect the cables and do chemical analysis for determining the degree of damage; ④ Regularly spread corrosion-resistant paint on the outdoor overhead cables.  

The anti-electrolysis corrosion methods include: ① reinforce the insulation between cable sheath and nearby giant metal object; ② install the drainage equipment and cathodic station; ③ install cover tube.   

4. On-line Monitoring

As the XLPE electric cables are extensively applied, its on-line monitoring technologies are also developing with more applications in foreign countries such as Japan. The operation condition of main insulation and sheath are monitored mainly from the aspect of some parameters, including voltage, current, quantity of partial discharge and working temperature etc.      

Major methods used now include earthing line current method, DC component method, DC superposition method, low-frequency superposition method, PD on-line monitoring method, cable temperature on-line monitoring method and moisture on-line monitoring method.  

5. Cable and Channel Anti-Fire

The cable fire accident caused by either external sources of ignition or its own faults is characterized by its violence, quick spread, difficult rescue and heavy loss. There are a variety of causes for cable fire, so it is hard to avoid them fundamentally. To avoid the heavy loss caused by cable fire accidents, on the one hand, hidden troubles of cable fire should be eliminated; on the other hand, high attention must be paid to countermeasures effectively against cable fire spreading. Now, a common fireproof method is to use fireproof materials to retard the fire, including fire retardant coating, fireproof blockage and packing.     

6. Prevent Small Animals from Destroying Cables 

In recent years, there has been an increasing number of cable accidents caused by termites. This case is likely to be neglected when laying the cables. The inspection of cables should be strengthened after local residents reflect to related department. If too many termites are found, this situation should be immediately reported to the superior and measures should be taken at once.