CN110940886A

CN110940886A - 110kV cross-connection cable fault diagnosis method based on differential current analysis

Info

Publication number: CN110940886A
Application number: CN201811117695.6A
Authority: CN
Inventors: 夏向阳; 赵威; 刘炎; 周正雄; 朱鹏
Original assignee: Changsha University of Science and Technology
Current assignee: Changsha University of Science and Technology
Priority date: 2018-09-25
Filing date: 2018-09-25
Publication date: 2020-03-31

Abstract

A110 kV cross-connection cable fault diagnosis method based on differential current analysis is characterized in that ground wire currents at a direct ground box and a cross-connection ground box are measured, ratio analysis and unbalance analysis are carried out on the ground wire three-phase currents under the fault and normal conditions to identify faults, and fault judgment bases and related databases are established according to a fuzzy control principle to carry out fault diagnosis. The method can overcome the defects of the traditional online monitoring and fault diagnosis method, has higher accuracy and can realize real-time diagnosis.

Description

110kV cross-connection cable fault diagnosis method based on differential current analysis

Technical Field

The invention relates to a 110kV cross interconnection cable fault diagnosis method based on differential current analysis, which is suitable for 110KV and above voltage levels and belongs to the technical field of electric power.

Background

The cross-linked polyethylene (XLPE) cable has the advantages of light structure, excellent electrical performance, convenience in laying and the like, and is widely applied to high-voltage power grids. In the operation process of the power cable, the power cable can be influenced by external complex environments, such as the action of multiple factors of electricity, magnetism, heat, chemistry, machinery and the like, and local defects of insulating air gaps, bulges and the like can exist in the manufacturing process, so that the insulation of the cable is gradually aged, and finally, local discharge is caused, and the main insulation of the cable is broken down.

In cable systems, most faults such as water trees, partial discharges, etc. cause insulation breakdown (permanent or transient breakdown so cable insulation is the most problematic part of a cable).

According to the operation and maintenance experience of a cable field, the phenomenon that the current of a cable sheath rises before the cable fault occurs is caused by many accidents, such as water inflow of a cross interconnection grounding box, corrosion of a cable body or an accessory metal sheath, damage of an outer sheath caused by external force damage, breakdown of an epoxy prefabricated part and the like. The cable sheath current is too high to cause the cable to heat up, thereby causing a large amount of additional loss on the sheath, reducing the current-carrying capacity of the cable, shortening the service life of the cable, and even causing thermal breakdown. Although engineering experience has shown that monitoring of sheath current can play an important role in cable monitoring, only a few researchers have so far used monitoring of sheath current as 1 important means for cable condition monitoring. When the line length of the high-voltage cable exceeds 1.2km, the line usually adopts a cross-connection mode to limit the induced voltage in the metal sheath of the cable and reduce the sheath current flowing through the metal sheath, thereby reducing the electric energy loss. The power cable cross-connection is 1 special interconnection mode that metal sheaths or shielding layers of cables of adjacent unit sections are connected in a cross mode, and a continuous loop of each metal sheath or shielding layer sequentially surrounds a three-phase conductor.

Research shows that the grounding circulation value is related to the load current value of the cable and the insulation resistance of the cable, so that the insulation condition of the cable can be judged by measuring the grounding circulation value. At present, the national power grid and electric power companies of all the places do not have a unified standard for specifying the normal and abnormal standards of the grounding circulation value. The standard of the Shanghai power company is that the current of a cable grounding wire is not more than 10A; the standard of the Hangzhou city electric power company is that the grounding circulation value cannot exceed 10% of the load current value; the national grid standard is a normal condition below 100A, an abnormal condition above 100-200A and a fault condition above 200A.

The above-mentioned standards are not versatile in practical situations because the arrangement of cables, length, load current, cross-sectional area, and voltage class all affect the circulating current. By analyzing the relevant examples, it can be found that the requirement of accurate monitoring of the operation of the current cable cannot be met by only measuring the size of the grounding circulation.

Disclosure of Invention

The invention aims to overcome the defects of the online monitoring and fault diagnosis method, and provides a 110kV cross-connection cable fault diagnosis method based on differential current analysis. The method identifies the fault by measuring the current of the grounding wires at the direct grounding box and the cross interconnection grounding box, carrying out ratio analysis and unbalance analysis on the three-phase current of the grounding wires under the fault and normal conditions, and establishing a fault judgment basis and a related database according to a fuzzy control principle so as to carry out fault diagnosis.

Firstly, collecting the grounding circulation of the metal sheath under the conditions of normal operation and failure of the 110kV cross-linked polyethylene cross-linked interconnection cable, and then calculating the change condition of the ratio or the unbalance degree. And judging the fault type by researching the ratio and the change of the unbalance degree according to different fault conditions.

The technical key of the invention is to calculate the ratio and the unbalance degree under fault and normal operation. The ratio is the ratio of fault current to normal current, and the unbalance is the average value of three-phase currents in the same grounding box, and the average value is subtracted from the maximum value of the three-phase currents and divided by the average value. The method needs to establish a cable track database as the basis for cable fault diagnosis.

Drawings

Fig. 1 is a schematic diagram of raw signal extraction of an online monitoring system.

FIG. 2 is a block diagram of an on-line monitoring system.

Fig. 3 is a schematic diagram of fault determination.

FIG. 4 is a monitoring system software interface diagram

Detailed Description

The invention is further described with reference to the accompanying drawings and the detailed description.

Referring to fig. 1, a cable sheath circulating current signal is extracted from the copper bars of the sheath cross-connect grounding box using rogowski coils.

Referring to fig. 2, a whole cable online monitoring system framework is shown in the figure, and each link of the system adopts a modular design and consists of the following three parts: the cable metal sheath grounding circulating current signal acquisition module, the signal wireless transmission module and the remote comprehensive information management system. The metal sheath circulating current signal acquisition module mainly comprises an original signal acquisition circuit, a filter circuit and a remote measurement and control terminal. The filtering circuit is used to eliminate high frequency noise in the signal and pass useful low frequency signal. Because harmonic waves, mainly third harmonic waves and fifth harmonic waves, exist in a power grid and affect the measurement accuracy, and even cause the system to oscillate, a trap circuit is used for eliminating third harmonic waves and fifth harmonic waves in signals. The signal wireless transmission module mainly transmits the related data monitored in real time to a remote integrated management system monitoring center. And finally, the monitoring center is responsible for receiving the current signals of the metal sheath acquired by the sensor.

Referring to fig. 3, after data is collected and transmitted to the computer, the monitoring device obtains a calculation result by using a ratio method and an unbalance calculation method, and then performs comprehensive judgment on the fault type by using a historical fault database as a reference.

Referring to fig. 4, the monitoring system calculates the three-phase current data effective value and solves the ratio and the unbalance degree to finally obtain the fault point and the fault type.

Claims

1. The 110kV cross interconnection cable fault diagnosis method based on differential current analysis is characterized by comprising the following steps of: the method comprises the steps of measuring the current of a grounding wire at a direct grounding box and a cross-connection grounding box, carrying out ratio analysis and unbalance analysis on the three-phase current of the grounding wire under the fault and normal conditions to identify the fault, and establishing a fault judgment basis and a related database according to a fuzzy control principle to carry out fault diagnosis. The method can overcome the defects of the traditional online monitoring and fault diagnosis method, has higher accuracy and lower cost, and can realize real-time diagnosis.