Electric Power Automation Equipment Power Cable Connector Failure Early Warning and Monitoring System Wang Xinchao, Pan Zhencun (School of Electric Power Engineering, Shandong University, Jinan 250061, Shandong, China) An in-line online evaluation algorithm for joint resistance and ageing has theoretically verified the correlation between joint temperature and joint quality. Sex. Based on this, the cable joint temperature monitoring system based on the above mechanism was introduced. The example analysis shows the effectiveness and credibility of the mechanism. At the same time, the advancedness and reliability of the system have also been verified.
In the power supply systems of cities and large and medium-sized enterprises, more and more power cables are used for transmission and distribution. When the power supply distance is long, cable joints usually appear on the line. Many years of operating experience show that more than 90% of cable operation failures are caused by joint failures. Through further analysis, contact resistance, overload and other factors are the main causes of the joint temperature is too high, resulting in insulation aging or chipping failure at the cable joints. For this purpose, we have developed a collection and distribution cable joint temperature monitoring system that can simultaneously monitor the temperature changes of multiple cable joints, real-time display, and timed printing and recording of the temperature values ​​of joints, and has a comprehensive analysis of alarm functions, so that operators can understand the cable in a timely and accurate manner. Operational situation, effectively avoid hidden accidents and ensure the safety of power transmission.
1 Theoretical Basis and Algorithm for Temperature Monitoring It has been proved in countless times that the joint temperature is the main parameter reflecting the quality of the joint. When the joint contact resistance increases, the joint temperature will inevitably increase. Longer-term higher temperatures can lead to insulation aging at joints. If the joint temperature is continuously detected and optimized, the changes in the quality of the joint can be analyzed and grasped in time to identify potential faults. In order to clarify the relationship between the resistance of the joint and the temperature, the following analysis was performed.
1.1 Joint heat source The joint heat is mainly the heat energy released by the current flowing through the circuit at the resistance of the joint. The heat energy is proportional to the square of the current flowing through the circuit and the resistance value of the joint.
1.2 Heat Transfer Heat is mainly transmitted in three directions, ie, the two sides of the guide line are passed and passed through the joint insulation. Due to the presence of thermal resistance, the temperature is distributed along the conductor at a certain gradient, the temperature at the joint is the highest, gradually decays to a certain distance to the ambient temperature, the heat transferred along the insulation of the joint, the heat resistance of the insulation skin and the thermal resistance of the air in a certain range. Transition to ambient temperature.
1.3 Electric Power and Thermal Hybrid Network The figure marked Ti stands for the temperature at the bare joint, T is the cable trench ambient temperature, TX is the measuring point temperature, Rx is the contact resistance at the joint, Ix is the cable current measured by the current transformer, and Rh is the cable The equivalent thermal resistance at the two ends is converted to the joint. Rm is the equivalent thermal resistance from the joint to the temperature detection unit. RH2 is the equivalent thermal resistance from the temperature detection unit to the ambient temperature. Because of the high voltage of the cable, considering the safety, ease of installation and cost, it is necessary to directly obtain the high cost of T. Therefore, the indirect temperature Tx is used in the subsequent analysis. The choice of components and materials is the thermal capacity of the temperature measuring element. To be small, high insulation and heat-conducting materials should be injected between the measuring points and the joints, and insulation materials should be used between the measuring points and the environment. After the above treatment, the calculation result using Tx instead of Ti actually proves that it can fully meet the requirements of engineering calculations.
1.4 Algorithms and Formulas According to the hybrid network and related theorems, the relationship between current, temperature and resistance can be deduced as follows: Example Correction factor.
Edge materials (higher-order polymers) can easily react with oxygen, which leads to lowering of the general use case when under the influence of temperature, light, and external forces. The 6-way scrolling WEDc monitor bookmark5 can be seen from the above formula. When the electrical equipment is in normal operation (its load current does not change greatly), the joint resistance is proportional to the temperature difference (Tx - T), which means that the cable head can be The temperature serves as a warning signal for cable head failures.
In addition to taking measures in time for cable heads in the event of an extreme warning, it is more meaningful to assess the quality of non-warning cable heads during equipment overhauls and to identify hidden dangers and solve them. Because repairs at this time will not affect production.
This kind of assessment mainly starts from the fact that the joint resistance has been changed, and the degree of joint insulation deterioration has begun. Due to the aging of the joint insulation, the insulation strength and the sealing performance will be reduced, and the leakage potential and the potential for shortening the service life of the joint due to the acceleration of the joint oxidation process will be hidden. Therefore, it is of practical value to properly evaluate the joint insulation aging. The following focuses on these two issues and discusses the basis and method of assessment.
In formula (1), because the initial value parameter is not easy to obtain (most of the temperature probes are added after the line is running, ie the technical improvement of the existing equipment), direct use is inconvenient. However, in engineering practice, it has been found that it is possible to identify hidden dangers by monitoring whether the joint resistance has changed significantly in the recent period of time. Assume that the connector performance is good before ti (generally the temperature probe access time can be used), and the ratio of the joint change can be obtained as a standard and the performance of the joint at a certain moment t2. When the ratio is available, it can be completely used as A detection device works independently, and its alarm temperature settings, print settings, collection channel settings, etc. can all browse the signal of each measuring point. This independent design is to reflect the characteristics of the distribution system, improve the reliability of the entire system. However, such on-site workstations do not have the evaluation software and graphic display capabilities, and their historical records are only alarm point records, and these optimization functions are implemented by the host computer.
The relay unit mainly has two functions: a. Downwardly according to the address number, it queries the on-site collection processing workstations or forwards instructions to the superiors, retrieves the information, and caches and forwards them; b. Obeys the settings and management of the superior computer. In the subordinate network, these settings include the number of access stations, address number, information content, transmission rate, and timing interval.
Both the observer watch station and the engineer station have query and print functions, but the work rights are different. In addition to the functions of the normal attendant observing station, the engineer station also has integrated functions such as alarm temperature setting, internal network configuration setting, and acquisition data management. The entire system can be connected to the internal LAN through network cards and hubs to obtain relevant data support.
3 Application Example Analysis 3.1 Temperature Alarm Example Fault Phase A Fault Line No.: Heavy Oil Hydrogen A8 3 (No. 3 Joint) Alarm Temperature: 65C History Record as (a). (May-July 998).
From the load current, there is a high current load in the two months before the alarm. After the query and maintenance record is the capacity increase and replacement of the A9 line, part of the load is incorporated into the A8 line. Fault conclusion: The original joint seal is not good, the water in the cable trench is wet, the joint part is corroded, and the load resistance is increased due to a load impact. Action: Remake the connector.
In this example, the temperature difference (Tx-T) curve at the cable head basically reflects the change of the joint temperature. Although this curve will be affected by the load current, it can still be used as a fault alarm signal. For on-site workstations (lower machines) with a relatively low environmental configuration and high reliability requirements, the temperature difference (Tx-T) curve is used as a basis for evaluation and is more convenient to use.
3.2 Insulation Update Assessment Example Fault Wire Number: Heavy Oil Hydrogen 6 1 (joint 1) Evaluation Recommendations Insulation Update B Phase; Recommended Level: Level 3; History Record As seen from the load current, approximately one and a half years before maintenance The load current is large and the temperature stays at 57*C for a long time. Theoretical analysis may be that the original resistance of the joint itself is high (although resistance evaluation has not given much change). Field surveys showed that the surface of the insulating layer had small cracks, and there were small holes inside the outer layer and there was pungent gas released. Conclusion: The quality of the original joint is not high, the joint temperature is high, and the insulation layer is prematurely aged. Remedy: Repair joints and insulation.
4 Conclusion The system has a complete data acquisition, transmission, processing, display, printing and long-distance communication capabilities, and is equipped with powerful software support, it can be seen from its design structure, it can not only be used for cable connector performance Dynamic monitoring can also be combined with other detection components to achieve real-time monitoring of various industrial control quantities. If gas sensors are used, the concentration of harmful gases can be monitored in cable trenches or other pipelines such as dangerous gases.
The system has been successfully put into trial operation of the heavy oil hydrogenation shut-off at the Qilu Petrochemical Shengli Refinery. For more than four years, the device has stable performance and good operating results. It has successfully detected hidden troubles three times, reduced direct losses by more than one million yuan, and indirectly lost millions of dollars, bringing huge benefits to enterprises and ensuring The safety of the plant's power grid and production has good promotion value.
Water treatment agent, Papermaking agent
YIBIN PERFEC INTERNATIONAL TRADE CO.,LTD , https://www.yibinbofei.com