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Insulation resistance measurement in cable engineering is very important
May 13, 2018

Due to the manufacturing process, transportation, site management and laying of power cables, there may be manufacturing process defects, poor transportation and storage, and damage to the laying process, which in turn may cause quality defects in power cables and affect the normal use of power cables. Therefore, in order to ensure the quality and reliability of the power cable before it is put into operation, the insulation resistance of the power cable must be measured before laying, after laying, and when the cable accessories are manufactured and installed. However, in the specific cable construction process, the construction workers often overlook the importance of insulation resistance measurement in cable engineering, and thus do not strictly perform insulation resistance measurement at various important points as required. This article through the case analysis of on-site incidents, discusses the importance of insulation resistance measurement in cable engineering construction, and aims to provide a practical basis for strengthening the strict operating awareness of cable insulation resistance measurement.


1 Cases


In December 2012, the author conducted insulation and AC withstand voltage tests for a 10 kV power cable from a model 110KV substation in Zhejiang Province that was rated YJLV22-8.7/15 and 3×500 mm2 to the customer. The total length of this cable is 2500 m and it consists of 5 500 m cables. When the author uses a 2500 V insulation resistance meter to measure the insulation resistance of the cable, the insulation resistance values of phase B and phase C at 1 minute are all greater than 10,000 MΩ, while the insulation resistance of phase A is zero. The analysis confirmed that there was a ground fault in the cable A phase. The reason was found that cable engineers did not conduct insulation resistance measurement tests on cables during cable laying and before and after installation and installation of cable accessories. After the cable fault tester test, the fault point in a cross-river. Excavation found that obvious cuts have appeared on the cable surface and the cross-linked polyethylene insulation of the cable has been severely damaged.


2 adverse events


Delayed work schedules prevented the power supply plan from being implemented on schedule. Due to the need to re-supply and manufacture intermediate attachments for cable faults, a cable well was additionally required for a total delay of approximately 20 days. Economic loss: In the process of finding and dealing with problems, the cost of failure point detection, the excavation cost of failure points, the cost of the purchase and production of cable attachments at the point of failure, and the cost of newly added cable wells should be involved.


3 Causes of the Incident


Basically, the most direct cause of the accident was caused by human factors. GB 50168-2006 “Code for construction and acceptance of cable installations for electrical installations” clearly stipulates that the requirements to be met before production of cable terminations and joints are: good insulation of cables. In this accident, due to the importance of neglecting the measurement of insulation resistance before the installation and installation of the cable accessories, the construction personnel did not perform the insulation resistance measurement on the cable in accordance with the requirements of the regulations, causing delays in the construction period and irreversible economic losses. In addition, the specific causes are analyzed as follows.


The quality consciousness of the production staff is not strong, and the possibility of defects in the production, transportation, management, and laying of the cable is underestimated.


No qualified professional has been assigned to measure and judge the insulation resistance of the cable in all important aspects of the cable project.


There is a defect in the management of the construction department. During the construction process, there is no record form for inspection of hidden work. Because there are management loopholes, there are loopholes in the work.


4 Summary and Suggestions


Insulation resistance measurement is the most direct method to judge whether insulation is good or not. Through the analysis and discussion of this incident, it further demonstrated the important role of insulation resistance measurement in cable engineering. In order to avoid the occurrence of similar incidents, cable production must strictly comply with the specified requirements, and conduct insulation tests on the cables in all important aspects of the project: test the cables on the cable before laying the cables to identify the manufacturing, transportation, and management of the cables. Whether there is a quality defect in the process; after laying, the cable accessories are tested before installation to identify whether there is any external damage to the cable during the laying process; after the cable accessories are manufactured and installed, tests are performed to identify whether there are quality defects in the accessories.


In addition, in order to ensure the strict implementation of insulation resistance measurement in cable engineering, the corresponding management system should be further improved.

 

The training courses for the construction of cable-related construction regulations will be added in order to increase the awareness of construction workers on the construction quality and the strict implementation of regulatory requirements.


Establish a practical cable construction management specification and work record form, and record the insulation test measurement data of each important part of the cable project.


Establish a corresponding responsibility system, implement responsibilities, and increase staff awareness of responsibility.


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