High-voltage cables of 110kV and above mainly use single-core cables, and their metal sheaths are generally interconnected and directly grounded at one end, and the other end is grounded through a sheath protector. These interconnections, sheath protectors, etc. are assembled in a box, which is a cable ground box.
Grounding boxes are divided into three types: direct grounding boxes, cross-interconnected grounding boxes and protective grounding boxes, which have been widely used.
The grounding box has the following problems during use:
Lack of circulating current detection and induced voltage monitoring functions. The manual inspection cycle is long, problems cannot be discovered in time, and the best opportunity for emergency repair is missed.
There are many incidents of grounding wires being stolen and cut. Once the ground wire is damaged or stolen, the voltage of the metal sheath will become a floating voltage, and its value may exceed the power frequency withstand voltage of the outer sheath of the cable, leading to breakdown. If the grounding box is stolen, it will be difficult to detect it in a short time.
Lack of cable joint temperature cannot be predicted. Due to reasons such as damage to the cable sheath, the cable temperature is too high, affecting line safety.
The cable trench environment is complex and there is a lack of real environmental data. Garbage in cable trenches is easily decomposed by microorganisms to produce methane and other flammable gases, which brings great hidden dangers to the operation of high-voltage cables; cable trenches are prone to water accumulation, and running cables in a flooded state will seriously affect the cable insulation and service life.
According to the "Technical Standards for Grounding Boxes for Cable Lines" and on-site operation requirements, the design of the cable sheath intelligent grounding box was completed. The entire system consists of the following parts:
Cable sheath intelligent grounding box
• Solar panels and energy storage batteries
• Sheath protector
• Voltage, current, temperature sensors
• Audible alarm
• External sensor (optional)
• Gas sensors: oxygen, methane, etc.
• Access control, water immersion, human body sensing
Management platform
• Personnel management, equipment management
• Data collection, data
